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.

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

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?

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: ?

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.