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To recap:
Some of us experience the following symptoms: - when it's very hot out (like 95F or higher) - driving at a medium speed (20-40 mph) - up a steep hill - arriving at a high altitude (5000' - 7000' )?
Positive symptoms: - strong raw gas smell (around the gas tank area, not from the engine compartment or tailpipe) - gas tank literally sounds/feels like it's boiling - pressure in gas tank (relieved if you open the gas cap)
Negative symptoms: - typically no CEL or codes via VCDS - van otherwise drives just fine - once the van cools down, starting and driving at altitude is normal
Background: - reports are more common with the 1997-2000 Eurovans vs. the 2001-2003 Eurovans (which have a redesigned Evap system) - this problem seems new - several of us who drive the same routes each year began to notice it 5-10 years ago. - some people report that it gets better with parts replacement (typically N80) - however, many of us have R&R many parts (Evap canister, N80 valve, gas cap, Oxygen sensors...) with no improvement.
Design flaw? The Eurovan's gas tank is right behind the engine, and with the right combination of factors (speed, temperature, altitude) you can get in a situation where tons of hot air are coming off the engine and radiator, blowing right by the gas tank, causing the gasoline to boil. ?Even if the N80 and evap system are working properly, gas fumes are created faster than the engine can burn them, eventually overloading the evap system leading to pressure release of gasoline fumes. ? ?An argument consistent with this is that the 2001 and later models have a beefier evap system, seem to be less likely to have this problem, suggesting that VW may have indeed fixed this flaw.
The main argument against this theory is that many of us feel like this is a new?problem that didn't happen when the van was younger, suggesting that something changed.
Malfunction? If something has changed, it's most logical to think something has worn out or broken in our vans. ?E.g., if the evap system were working better, the problem would go away. ??
The main argument against this theory is that several of us have R&R multiple parts and never found a cure.
Could it be the Gasoline? Perhaps something else has changed? ? If the fundamental problem is gasoline boiling in the gas tank, perhaps gasoline formulations have changed to increase the vapor pressure??
In fact, around 2003 California phased out MBTE and started using about 5% Ethanol, and around 2010 rules changed to allow up to 10% ethanol in California fuel blends. ??
It so happens that E10 gasoline is allowed to have a Reid Vapor Pressure (RVP) up to 1 psi higher:?
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On Tue, Apr 4, 2023 at 11:31 AM, Michael Diehr wrote:
If the fundamental problem is gasoline boiling in the gas tank
I believe this is because the vapor can't escape, building up pressure.? That all goes back to the EVAP system not operating properly. -- Duane 05HD Rialta 220K Miles
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On Apr 4, 2023, at 11:24 AM, Duane <txpigeon@...> wrote:
On Tue, Apr 4, 2023 at 11:31 AM, Michael Diehr wrote:
If the fundamental problem is gasoline boiling in the gas tank?I believe this is because the vapor can't escape, building up pressure.? That all goes back to the EVAP system not operating properly.?
--?
Duane
05HD Rialta
220K Miles The idea that the EVAP system is malfunctioning is very logical and I'm not ruling it out, but I am leaning towards other explanations.
Pressure release / vent failure? Pressure increases the boiling temperature for all liquids - so if the gasoline in the tank is boiling, it's actually not under enough pressure. (Or, it's just way too hot)?
The EVAP system has a LDP (leak detection pump), and although it's vacuum operated, it tests for leaks by holding a positive pressure. ? In my van there are no LDP codes in normal operation, but I've accidentally triggered the "small leak" and "large leak" codes when I was messing around, which leads me to believe the LDP is working, and my system is tight.
I believe in the Eurovan the LDP is dual purpose, and is also the vent. ?From the same guide:?
The LDP is integrated into the EVAP system and can have two functions. The LDP can: ? pressurize the EVAP system and detect a drop in pressure that would indicate a leak ? function as the EVAP Canister Vent on vehicles that do not have a separate EVAP Canister Vent.
I'm not clear what happens if the system gets over pressured - does the LDP vent have some sort of safety blowoff valve? ?Could that blowoff valve have failed somehow? ?
Capacity Logically, the evap system does not have infinite capacity to deal with vapor.
For example, the evap guide you referenced says:
A 1% concentration of fuel vapor from the EVAP Canister can vary the air/fuel mixture by as much as 20%. This can have a drastic effect on engine driveability and vehicle emissions.
I think it's quite possible that this system has a limit, and there is some combination of heat, altitude, and gasoline volatility which could overwhelm the system, so the purge can't keep up, and eventually the pressure is released, even if the system is 100% functional as designed. ??
Under this theory, VW designed the 1997-2000 evap system to handle "normal" conditions, but gasoline changes in the last decade were not something they planned for.
As I say, I'm not sure of any of this, just trying to get more data and see what theories fit the evidence...
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On Tue, Apr 4, 2023 at 03:21 PM, Michael Diehr wrote:
Pressure increases the boiling temperature for all liquids
But...? Increased pressure also causes increased temperature.? I've never run across anyone with a properly working EVAP system that had "boiling" or excess pressure.? Mine acted up once, but it turned out to be the N80 clogged, so pressure built in the system.? Since the N80 cycles constantly after the engine warms up, there should be no way for it to build pressure. -- Duane 05HD Rialta 220K Miles
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On Apr 4, 2023, at 2:13 PM, Duane <txpigeon@...> wrote:
Pressure increases the boiling temperature for all liquids But... Increased pressure also causes increased temperature.
I've never run across anyone with a properly working EVAP system that had "boiling" or excess pressure. Well, there may be at least two of us on this very email list saying it's happening to us. :-) Mine acted up once, but it turned out to be the N80 clogged, so pressure built in the system.
Since the N80 cycles constantly after the engine warms up, there should be no way for it to build pressure. Was this in your 2005 Rialta? What were the conditions (air temperature, altitude...) I think it's possible that we are seeing different scenarios: (A) a clogged or broken N80 will cause these symptoms under relatively benign conditions (low altitude, warm but not hot) (B) in the 1997-2000s, a perfectly working evap system can get overwhelmed under rare conditions. Mike p.s. thanks for engaging on this, I appreciate the back & forth ideas...
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Dear friends:
Michael Diehr described the symptoms thus:
Some of us experience the following symptoms:
- when it's very hot out (like 95F or higher)
- driving at a medium speed (20-40 mph)
- arriving at a high altitude (5000' - 7000' )?
- strong raw gas smell (around the gas tank area, not from the engine compartment or tailpipe)
- gas tank literally sounds/feels like it's boiling
- pressure in gas tank (relieved if you open the gas cap)
- typically no CEL or codes via VCDS
- van otherwise drives just fine
- once the van cools down, starting and driving at altitude is normal
- reports are more common with the 1997-2000 Eurovans vs. the 2001-2003 Eurovans (which have a redesigned Evap system)
- this problem seems new - several of us who drive the same routes each year began to notice it 5-10 years ago.
- some people report that it gets better with parts replacement (typically N80)
- however, many of us have R&R many parts (Evap canister, N80 valve, gas cap, Oxygen sensors...) with no improvement.
I will just tell you that I had this identical constellation of problems in my 1997 EVC that started in July 2014 when my van had 139,000 miles.?
I replaced the fuel tank cap and associated seals and hose clamps. I replaced a bad check valve and the gas tank with a new one in July 2014; then replaced the gas tank again under warranty (for the 2014 tank) in July 2015 and I replaced the carbon cannister at the same time. The EVC then had 147,000 miles. I also removed the belly pan to give better ventilation to the engine so that the heat is not all directed around the gas tank.
The problem described did continue, despite all this. I am told by my current mechanic that this problem was fixed in the 2000-2003 EVCs, as the vapor recovery system was changed substantially and there is no longer a tail on the carbon canister that exhausts fumes directly onto or into the frame when the canister cannot absorb all the vapor.
Gas fumes can be caused by a variety of things. Some of those things, are fixable. I am going to paste below a string of comments from the VW list in 2014-2021 on the topic, and you will see the comments, a fix or two for certain causes, and the frustration that this has caused:
Wolfgang Baudler, EV list, August 29. I had the same problem as the original poster with fuel fume smells inside and outside on my 1995 EV. Smell was intermittent, seemed to depend on temperature, weather etc and also was more pronounced when going uphill. ? In my case it turned out to be a broken breather tube, the line connecting the top of the fuel tank with the EVAP canister.? ? It was broken at an inaccessible location near the top of the tank. Took a long time to track this down, but once I have replaced that breather tube the fume smells went away. The whole line was very brittle, so possible that this might be the cause for others as well. ? I managed to replace it without dropping the tank, but you will need to cut the carpet in the cabin for access to the top of the tank. It would be much easier to inspect and replace with the tank dropped. ? Part number for the 95 is 7D0-201-059-C? ? Wolfgang ? From: "websailn2@...?[ev_update]" <ev_update@...> To:?ev_update@... Sent: Wednesday, August 20, 2014 1:51 PM Subject: [ev_update] Re: Fuel Evap System for 1997 Eurovan ? ? There are a few diagrams of the system in the Bently Manuals, but not much of a description of operation. Without doing some more study here is a general summary off the top of my head of how things work: In your fuel tank, you have liquid on the bottom and vapor on top of that. As you refill the tank, adding more liquid, the vapor needs somewhere to go. In the old days, it just vented into the environment around the side of the fill nozzle. Now, for environmental reasons, it's forced into a charcoal canister, where the vapor is adsorbed. Later, when the engine is running and up to operating temperature, the canister is connected to the intake manifold by a valve that allows the vapor to be drawn off and burned, cleansing the canister for the next refueling cycle. There are a number of check valves in the filler neck assembly that allow this to happen as described and you can stare at the Bentley diagram for a long time trying to figure it out. ? One issue regularly reported, is overfilling the tank thereby pushing liquid into the canister. The liquid turns the charcoal granules into a solid briquette which will block the canister, sending the vapor out around the nozzle like the old days. You'd smell it, but also likely experience the gas pump nozzle clicking off a lot. Doesn't sound like you have that problem. ? Alternately, the canister may have lost some of it's "storage" capacity. It may be "full" because the stored vapor is not being drawn off because of a blockage in the system or a failure of the vapor recovery valve. You'd smell this too - the canister is behind the driver side wheel and has a breather tube that would expel any excess vapor that couldn't be adsorbed. However, I recollect there is a self test of the system on start up so you'd get a check engine light if this is the problem - I think. ? Finally, over time, the charcoal granules get pulverized so there is more void volume in the canister, less adsorption surface - again less vapor storage capacity. So any vapor that couldn't be adsorbed would also pass out the canister's breather and you'd smell that. ? One more obscure thing: some people have mounted things under the front seat - stereo amps and such, inadvertently drilling through the top of the tank. That would give you a gas smell but most of the time though, not just during refueling. ? I have heard of the trick of leaving the gas cap off to "dry out" the canister but I don't think this actually works. One, I don't believe the system check valves are oriented to allow this and two, a damage canister (solid brick or excess void) can't be restored with just an airing out. ? If you problem is persistent, a new canister is probably the easiest solution. If it isn't affecting drivability, it's just an environmental issue. ? OK, lost my head on this post. I need a life. ? Regards, Duane? 2000 EVC ? Thread on the issue on Eurovan FB page Feb. 18, 2021Hello, I own a T4 shop and we see this often. We see dirt/debris/insect nest clog the breather lines, cracks in the tank and/or hoses. A saturated canister / stuck purge/evap check valve can also cause this. ? Tom Smith My 2002 is doing the same thing currently.?? ? Terry Schmerk My 99 had the same problem..replaced the gas tank..problem solved ? Chelo Cobian Terry Schmerk cost? Like ?· Reply · 14h Terry Schmerk Chelo Cobian the tank was only 75...out of a used one from a scrap yard...this was in Toronto..shipping for it was about the same amount ? Chelo Cobian My 2000 has that same smell...sometimes. had shop check it out and they found no cracks or leaks and everything working fine?? ? Obaid Zamani Snow and ice / Debris dirt there’s breather lines by your rear wheel for your gas tank I had this issue years ago over the winter in northern Virginia ? Gary Lewis I had a the same issue. My issue was pressure buildup in the tank when I removed the cap just as you stated. I could smell gas at times before removing the cap. It turns out that there is a small valve that gets pushed in when the gas cap is inserted. The gas vapors are then released into the charcoal canister etc. All i had to do is carefully bend the flat metal v shaped valve out a bit so when the gas cap was inserted the valve would open into the line and release the tank pressure. It's on the left inside. Hope that makes sense. ? Chelo Cobian Gary Lewis anyway you can take a pic and point to it? ? Mark O'Neil Conner '95 EVC, here. Been to this movie. My mechanic replaced the fuel line, it was badly corroded. Problem solved. ? Corporal Ninny I have a ‘97 with 190K had a similar issue and replaced my gas cap which solved the problem - I bought this cap off ebay but don’t see it listed anymore it was just under $15 May be an image of text that says 'Item info Seat VW I $14 Shipping ad'
Macon Cowles
Boulder
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Hi, long time lurker. Don't think I have ever posted.
2000 EVC with the EXACT same issue/ symptoms as?Michael Diehr has related. Problem really only happens on one road traveling to somewhere I like to camp. Things I have done: Used this forum and online references to test the evap canister and system. Could not find anything wrong. Would have replaced it if it was still?available. Replaced gas cap. Wrapped the exhaust piping with fiberglass heat tape before and after the cat near the gas tank. Insulated most of the exposed surfaces of the gas tank with adhesive backed foil heat reflecting material. Replaced the radiator. Removed the engine oil based transmission cooler and replaced it with a tranny cooler in front of the radiator.? AND added a second, thermostatically controlled tranny cooler with a fan, located aft of the gas tank. Nothing I have done has had any effect except for somewhat lower engine and trans temps, as monitored with a Scan gauge. Still gets hot, has exterior gas smell, excessive gas tank pressure, and boiling/gurgling noises from the gas tank when going up that road.? I have learned to monitor temps when going up that road and stopping at a couple of convenient?places on the way up. I carefully?vent the gas tank, and wait for the engine and tranny cooler fan to stop running before proceeding. May contemplate?replacing the gas tank per the post that had luck with that. The change in gasoline properties?seems as likely as anything. Giving up trying to do anything more to mine for the time being. Just waiting for the definitive?fix posted here.
Don Daynes? Anaheim, CA ?
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Macon, Don, and others, thank you all so much for joining the discussion!
It's nice to know I'm not alone, and maybe with more minds and more data, we can figure this out?
Mike
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On Apr 6, 2023, at 2:32 PM, Don Daynes <ddaynes@...> wrote:
Hi, long time lurker. Don't think I have ever posted.
2000 EVC with the EXACT same issue/ symptoms as?Michael Diehr has related. Problem really only happens on one road traveling to somewhere I like to camp. Things I have done: Used this forum and online references to test the evap canister and system. Could not find anything wrong. Would have replaced it if it was still?available. Replaced gas cap. Wrapped the exhaust piping with fiberglass heat tape before and after the cat near the gas tank. Insulated most of the exposed surfaces of the gas tank with adhesive backed foil heat reflecting material. Replaced the radiator. Removed the engine oil based transmission cooler and replaced it with a tranny cooler in front of the radiator.? AND added a second, thermostatically controlled tranny cooler with a fan, located aft of the gas tank. Nothing I have done has had any effect except for somewhat lower engine and trans temps, as monitored with a Scan gauge. Still gets hot, has exterior gas smell, excessive gas tank pressure, and boiling/gurgling noises from the gas tank when going up that road.? I have learned to monitor temps when going up that road and stopping at a couple of convenient?places on the way up. I carefully?vent the gas tank, and wait for the engine and tranny cooler fan to stop running before proceeding. May contemplate?replacing the gas tank per the post that had luck with that. The change in gasoline properties?seems as likely as anything. Giving up trying to do anything more to mine for the time being. Just waiting for the definitive?fix posted here.
Don Daynes? Anaheim, CA ?
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More thoughts/questions about this problem.
Why is the fuel boiling in the gas tank? ?There are 3 reasons a liquid will boil: Head, Pressure, and Chemical composition.
Heat Too much heat is getting into the fuel. ?This is consistent with many reports that this happens when air temperature is hot, driving with air conditioning on, and driving uphill (which increases engine output and heat) and driving at a moderate speed. ?My theory is that when going slow enough, the airflow from the engine and radiator hits the gas tank exactly at the right angle (so the air hitting the tank is near 220F). ?However, if you are going faster, there is more ambient air to dilute the hot air from the engine, so the air hitting the tank is closer to 100F ambient.
Are there other sources of heat?
Mixture / Catalytic Converter: the cat is located near the right end of the gas tank. ?If the van is running rich, the cat will be extra hot, which could dump more heat into the tank. ? However, Don reported "I Insulated most of the exposed surfaces of the gas tank with adhesive backed foil heat reflecting material." which did not fix the problem.
Are there other sources of rich-running which do not trigger a CEL?
- bad Oxygen sensor (however, several reports that replacing Oxy sensors did not fix the problem)
- PCV valve - just today, a report of a failed PCV that did not trigger a CEL, but lead to a chronic rich-running condition: ? /g/eurovanupdate/message/163832
- leaky fuel injectors ???
Fuel Return: the fuel pump moves fuel to the injector manifold and then back to the tank. ?It seems like this round trip to the engine compartment and back would heat the fuel. ?Is there some failure mode where more fuel is flowing than normal, thus picking up much more heat? ? Is there some design change in the 2001 and later vans which reduces this problem?
Pressure A liquid's boiling temperature goes down with lower pressure. ?Most reports say it happens at altitude (personally, I've seen it at about 4000' up to 9000'). ?The fuel system is sealed and should hold pressure, and most reports say that opening the gas tank releases a lot of pressure, and almost nobody is having CELs showing small or large leaks. ? ?
However, perhaps there is some other part ?that is supposed to hold pressure but is failing at high enough pressure? ? For example, here's a video showing that an o-ring gasket in the gas tank filler tube neck can fail: ?
Chemical A liquid's boiling temperature depends on the liquid itself, and as previously mentioned, California gasoline formulations have changed over the years, and in particular Ethanol increases the vapor pressure. ?Summer gasoline blends are supposed to reduce the vapor pressure, but perhaps there are some gas stations still selling winter blends in the summer? ?I've not noticed any pattern with where I fill up with gas, other than that I usually fill up in Bishop CA heading to the sierras (but I've also had this problem heading to Joshua Tree). ? I feel like the problem is more likely to happen when the gas tank is closer to full vs. empty, but I'm not sure that makes sense.
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Important data points to solving this problem:
1. What is the year of the Eurovan? 2. When did the issue first arise?? 3. Age of Eurovan when the problem arose? 4. Mileage on Eurovan when the problem arose? 5. Geographic area where it is a problem? 6. Season when it is a problem
My Answers:
1. 1997 2. Spring 2014 3. 17 years 4. 139,000 5. Colorado plateau 6. mostly summer, but some fumage detected spring and fall
Because of my experience, I think that the carbon canister, which no longer can be purchased, must be the major culprit. After all, this vehicle worked just fine for 17 years and 139,000 miles, traveling in the same territory, experiencing similar heat.?
Macon Cowles
1726 Mapleton Ave.
Boulder, Colorado 80304
macon.cowles@...
(303) 447-3062
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On Wed, Apr 19, 2023 at 01:10 PM, Macon Cowles wrote:
I think that the carbon canister, which no longer can be purchased, must be the major culprit
I'd tend to agree, but maybe not directly.? The little carbon pellets have been vibrating/rubbing for many years, creating dust.? On mine, it was the dust that stopped up the N80 valve.? Replacing/rebuilding the canister might have solved it once and for all, but instead, I installed a filter (NAPA Gold 3002) on the line in front of the N80.? I've changed it 3 times now because of the dust it accumulates. -- Duane 05HD Rialta 220K Miles
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Macon, thanks for the input. ?I think there are a few more variables we should consider.
Back in June 2019 I did the exact same trip on two different weeks. ? The last 30 miles of this drive are a long, slow uphill to the campsite (from about 5000' to 7500'). Conditions were almost exactly the same (weather: 92F vs 93F).
Fir the first drive I had strong gas fumes ?For the repeat, zero fumes.
The only difference? - in the first trip, I filled with gasoline 30 miles from the destination. ?Strong gas fumes when I reached the campsite. - in the second trip, I filled with gasoline 75 miles from the destination. ?No gas fumes.
I think we should also consider the gas tank conditions (was it filled recently? how full when fumes are venting?)
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On Apr 19, 2023, at 9:22 AM, Macon Cowles <macon.cowles@...> wrote:
Important data points to solving this problem:
1. What is the year of the Eurovan? 2. When did the issue first arise?? 3. Age of Eurovan when the problem arose? 4. Mileage on Eurovan when the problem arose? 5. Geographic area where it is a problem? 6. Season when it is a problem
My Answers:
1. 1997 2. Spring 2014 3. 17 years 4. 139,000 5. Colorado plateau 6. mostly summer, but some fumage detected spring and fall
Because of my experience, I think that the carbon canister, which no longer can be purchased, must be the major culprit. After all, this vehicle worked just fine for 17 years and 139,000 miles, traveling in the same territory, experiencing similar heat.?
Macon Cowles
1726 Mapleton Ave.
Boulder, Colorado 80304
macon.cowles@...
(303) 447-3062
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Santa came early, and I'm now the proud owner of a Ross-Tech Hex-V2, so I can run the real version of VCDS. I had been running the shareware/Lite version, which has limited features.
I've already verified the N80 is mechanically functional (both with manually applied 12V, as well as doing Sequential Output tests where I can hear the N80 clicking). My carbon canister is brand new, and air flow through the evap purge line flows freely (when the N80 is open). The van has no CEL or other DTCs.
Is there any way to watch the N80 duty cycle in real time as I drive? I have an oscilloscope so could tap into the electrical connector, but it would be neat to do it using VCDS measuring blocks.
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Back in digest #712 Macon Cowles posted a great compilation of many people's experience with gas fumes, gurgling, and gas tank pressure when hot, especially at altitude. The one that caught my eye was this excerpt from Gary Lewis:
I had a the same issue. My issue was pressure buildup in the tank when I removed the cap just as you stated. I could smell gas at times before removing the cap. It turns out that there is a small valve that gets pushed in when the gas cap is inserted. The gas vapors are then released into the charcoal canister etc. All i had to do is carefully bend the flat metal v shaped valve out a bit so when the gas cap was inserted the valve would open into the line and release the tank pressure. It's on the left inside. Hope that makes sense.
This easy repair "may" have fixed mine. I will withhold final judgment until I take the van up my problem road. This past weekend I took the van up to Yosemite before the park was closed due to flooding. During the trip up the mountain the ambient temp was not that hot but I was still surprised that when I stopped there were no gas fumes or pressure in the tank. The trip home was unseasonably warm through the central valley and I saw 210 degree engine temps going up the Grapevine. Again, after stopping at the first rest stop, there were no fumes gurgling, or tank pressure.?
My valve actuator is at the top of the filler not the left as described by Gary. The material is very springy and hard to bend. My efforts were to 'influence' the actuator closer to the center and to pull it out toward the camera in this photo. Think about? insuring the gas cap makes contact and fully opens whatever valving is going on inside as I was unable to figure out exactly what is was actually doing.
Fingers crossed.
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Hi Don, that's good news (if it holds).
Speculating about how this could be happening, I realize I really don't understand how the Evap system works, especially all the parts on the gas tank that come before the Canister.
Here's a picture of a Eurovan fuel tank with all the evap hoses attached. ?
Don (and others) are saying that a problem with #3 (Breather Valve) could cause fumes to build up. ?This would make sense, but only if the 3,4,5,6 pathway is the only way for fumes to get to the canister.
However, there appears to be another pathway (9, 10, 11, 12, 7).
Could we be having a situation where both pathways are blocked?
Please help me ID these parts:
1. tank vent to breather bottle 2. Breather Bottle 3. is this the Breather Valve (?) 4. is this the Rollover valve (?) 5. ? is this tube normally open or closed? 6. is this the tube that lets you see and drain liquid gasoline? 7. Is this a valve? or just a T-connetor? 8. check valve? 9. another vent? 10. yet another vent or part? ?One side looks open to the atmosphere - is this an overpressure release? ?Perhaps where our fumes are coming from? 11. Mystery part - seems to take inlets from #9 and #10 ?What's in the box? 12. is this tube normally open?
Source:?
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On May 4, 2023, at 3:41 PM, Don Daynes <ddaynes@...> wrote:
Back in digest #712 Macon Cowles posted a great compilation of many people's experience with gas fumes, gurgling, and gas tank pressure when hot, especially at altitude. The one that caught my eye was this excerpt from Gary Lewis:
I had a the same issue. My issue was pressure buildup in the tank when I removed the cap just as you stated. I could smell gas at times before removing the cap. It turns out that there is a small valve that gets pushed in when the gas cap is inserted. The gas vapors are then released into the charcoal canister etc. All i had to do is carefully bend the flat metal v shaped valve out a bit so when the gas cap was inserted the valve would open into the line and release the tank pressure. It's on the left inside. Hope that makes sense.
This easy repair "may" have fixed mine. I will withhold final judgment until I take the van up my problem road. This past weekend I took the van up to Yosemite before the park was closed due to flooding. During the trip up the mountain the ambient temp was not that hot but I was still surprised that when I stopped there were no gas fumes or pressure in the tank. The trip home was unseasonably warm through the central valley and I saw 210 degree engine temps going up the Grapevine. Again, after stopping at the first rest stop, there were no fumes gurgling, or tank pressure.?
My valve actuator is at the top of the filler not the left as described by Gary. The material is very springy and hard to bend. My efforts were to 'influence' the actuator closer to the center and to pull it out toward the camera in this photo. Think about? insuring the gas cap makes contact and fully opens whatever valving is going on inside as I was unable to figure out exactly what is was actually doing.
Fingers crossed.
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Also, I notice a small discrepancy - the check valve which I labeled "#8" doesn't show up in official VW parts. ?
From the image (which may be a 2001 or later fuel tank?)
From the VW Parts Catalog (supposedly for a 2000 Eurovan):
Perhaps a model year difference?
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This video is helpful in understanding evap system operation. https://youtu.be/y4heTf4rz7A
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On May 7, 2023, at 2:25 PM, rmartin1962@... wrote:
This video is helpful in understanding evap system operation. https://youtu.be/y4heTf4rz7A
The video begins by describing the pre-1998 systems, which are simpler than our vans, and missing quite a few parts.
However, at 24.5 minutes it introduces the?Onboard Refueling Vapor Recovery (ORVR) system. Link: ?Link https://youtu.be/y4heTf4rz7A?t=1483
Staring in 1998, the ORVR system adds some new parts:
Filler Breather Bottle Pressure Holding Valve Various tubes to connect
My rough transcription from the video:
During normal operation, the ORVR works the same as previous systems. ?Fuel vapors are collected in both bottles, then routed through the breather valve, then to the rollover valve, then on to the pressure-holding valve (PHV). ?The pressure-holding valve controls the amount of fuel tank pressure by keeping a small amount of pressure on the fuel in the fuel tank, so that fewer vapors are formed. ?When the tank pressure gets high enough, the PHV opens, allowing vapors to reach the evap canister. ? The PHV also allows air from the evap canister vent into the fuel tank to relieve the vacuum created in the fuel tank as fuel is pumped to the engine. When the evap purge (N-80) is open, the PHV will close, preventing fuel vapor from being drawn directly out of the tank. During refueling, the nozzle from the gas pump pushes aside the fuel tank filler flap, which pushes on the breather valve, closing the path from the operating breather bottle, trapping air in the breather bottle and and the top of fuel tank, to allow for expansion. ?At the same time, the larger vent line from the filler breather bottle is opened. ?Vapors from refueling will be forced from the tank, into the filler breather bottle, and on to the evap canister.
Based on this added complexity, I can imagine a few failure modes:
A. what if the breather valve doesn't open, or doesn't open fully?? This could cause the symptoms seen by Gary and Don: fumes from the tank would be blocked or restricted in reaching the evap canister. ?Bending the metal part in the filler neck so that the gas cap more fully opens the breather valve would be the solution.
B. what if the pressure-holding valve does not open at the right pressure, or does not open fully? This might cause similar symptoms, as the path to the evap canister would be restricted or blocked. ? Fixing this would probably require dropping the fuel tank?
C. what if the valve to the filler breather bottle does not close? ? I'm less sure about this scenario. ?The filler breather bottle pathway is normally closed, so having this one fail open would actually create an additional path from the tank to the evap canister. ?This would seem to be the opposite of what we are seeing. ?However, this additional path also bypasses the pressure-holding-valve, which could leave the tank at a lower pressure, which could lead to increased fume generation overall, which might be expected to make the symptoms worse? ?
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I have also experienced that noted symptoms of high tank pressure and boiling sound on occasion at elevation in warm temperatures in my 1999 EVC with no fault codes. Being from Minnesota it happens very rarely and only when traveling west into the mountains. However, following is my latest hypothesis on the cause.
It is my understanding from viewing limited photos of a carbon canister that was cut open, there are vertical chambers in the canister, connected in series, to provide an effective/longer treatment path of vapors flowing through the carbon. For whatever reason, say overfilling or a component issue (e.g., evap purge valve or vent valve problem), the carbon canister becomes saturated with liquid fuel essentially creating a liquid trap in the bottom of the canister thereby restricting or blocking vapor flow during tank venting and carbon purge/recharge events. In moderate elevation or temp changes there is not enough pressure differential to create any notable symptoms of an issue. In higher temperatures and/or elevation changes, pressure builds up to the point that it overcomes the liquid trap in the canister creating the boiling/bubbling sound and high vapor levels/smell that is likely being emitted from the vent line when the engine is off. Moreover, because of this liquid trap or super saturation, recharge of the carbon canister can't occur effectively because the liquid trap blocks or restricts the flow of fresh air during purge/recharge events potentially causing further saturation and/or liquid accumulation in the canister.?
Again, this is only a hypothesis but seems quite plausible to me as a starting point to further evaluate if and when this reoccurs in my case. Sure would love to see better detailed photos on the interior of the carbon canister to confirm configuration and vapor flow pattern along with confirmation that the boiling/bubbling sound is coming from the base of the carbon canister and not the fuel tank.
What could be the fix? Remove the carbon canister and manually purge any liquid fuel/saturation, repair or confirm evap purge and vent systems are working as designed, and try not to overfill the gas tank during refueling. Cheers, Bob
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Hi Bob,
Thanks for the input!?
I'm pretty sure there are multiple causes, which is why it's so confusing to diagnose. ?
Regarding the canister: when I took mine apart, it was dry, and the carbon granules were in pretty good shape.?
However there are several filters which were somewhat clogged with dust. ?I washed everything out and put it back together and it definitely flowed better. ?You can see my writeup here: ??and in particular, one of the 8 filters is shown in picture #7.
Unfortunately, this did not solve my issues, so I went ahead and replaced the canister completely with a brand-new GM part: ?
This made a big improvement, but still didn't fix the problem 100%, which is why I'm still looking for other causes, such as N80 problem, breather valve malfunction, etc.
Mike
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On May 9, 2023, at 8:56 AM, rmartin1962@... wrote:
I have also experienced that noted symptoms of high tank pressure and boiling sound on occasion at elevation in warm temperatures in my 1999 EVC with no fault codes. Being from Minnesota it happens very rarely and only when traveling west into the mountains. However, following is my latest hypothesis on the cause.
It is my understanding from viewing limited photos of a carbon canister that was cut open, there are vertical chambers in the canister, connected in series, to provide an effective/longer treatment path of vapors flowing through the carbon. For whatever reason, say overfilling or a component issue (e.g., evap purge valve or vent valve problem), the carbon canister becomes saturated with liquid fuel essentially creating a liquid trap in the bottom of the canister thereby restricting or blocking vapor flow during tank venting and carbon purge/recharge events. In moderate elevation or temp changes there is not enough pressure differential to create any notable symptoms of an issue. In higher temperatures and/or elevation changes, pressure builds up to the point that it overcomes the liquid trap in the canister creating the boiling/bubbling sound and high vapor levels/smell that is likely being emitted from the vent line when the engine is off. Moreover, because of this liquid trap or super saturation, recharge of the carbon canister can't occur effectively because the liquid trap blocks or restricts the flow of fresh air during purge/recharge events potentially causing further saturation and/or liquid accumulation in the canister.?
Again, this is only a hypothesis but seems quite plausible to me as a starting point to further evaluate if and when this reoccurs in my case. Sure would love to see better detailed photos on the interior of the carbon canister to confirm configuration and vapor flow pattern along with confirmation that the boiling/bubbling sound is coming from the base of the carbon canister and not the fuel tank.
What could be the fix? Remove the carbon canister and manually purge any liquid fuel/saturation, repair or confirm evap purge and vent systems are working as designed, and try not to overfill the gas tank during refueling. Cheers, Bob
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Duane
