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Overheating 3.0 V6 Toyota Truck

 

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My 1993 Dolphin with a 3.0 V6 automatic transmission always overheats on hills. Anytime we are climbing a hill it gets too warm, going downhill it cools off again.? It also heats up when you are pushing the engine, going fast on level ground, even on cool day. The gauge is nudging the red zone. So far, I have replaced the three-row radiator, the thermostat and the fan clutch.? I've even removed the front license plate. It was blocking a small air supply slot in the bumper. None of this has helped.? When I replaced the thermostat, I expected sludge, but the port and the thermostat was clean as a whistle. I intend to flush the system, but it seems very clean already.? I'm contemplating replacing the water pump (huge job). The pump doesn't leak, and the bearing seems sound (no play). Is this a common problem with the V6 engines or am I missing something? Has anyone else had this problem and if so, how did you solve it?

Jeff Cardinal
 

While running. Pull one spark plug wire off the distributor cap, one at a time and replace. Make note of rpm drop for each cylinder. If one cylinder does not drop rpms when off distributor cap, then that is your issue.
Loosen plug wires first and use a wood tool with right hand to reduce shock hazzard. Keep rest of body off car.
Good luck and may all your cylinders fire.


On Fri, Mar 14, 2025, 11:59 PM Rhonda CARDINAL via <jwcardinal=[email protected]> wrote:
My 1993 Dolphin with a 3.0 V6 automatic transmission always overheats on hills. Anytime we are climbing a hill it gets too warm, going downhill it cools off again.? It also heats up when you are pushing the engine, going fast on level ground, even on cool day. The gauge is nudging the red zone. So far, I have replaced the three-row radiator, the thermostat and the fan clutch.? I've even removed the front license plate. It was blocking a small air supply slot in the bumper. None of this has helped.? When I replaced the thermostat, I expected sludge, but the port and the thermostat was clean as a whistle. I intend to flush the system, but it seems very clean already.? I'm contemplating replacing the water pump (huge job). The pump doesn't leak, and the bearing seems sound (no play). Is this a common problem with the V6 engines or am I missing something? Has anyone else had this problem and if so, how did you solve it?

Jeff Cardinal
 

Check the ignition timing, it could be retarded.
 

Yes, exactly the same. Believe it or not Dave (forgot his last name,sorry) in California told me to replace my catalytic converter. That fixed the problem. Even running a straight pipe did not work. Everything is good now.?

On Sat, Mar 15, 2025 at 1:59?AM Rhonda CARDINAL via <jwcardinal=[email protected]> wrote:
My 1993 Dolphin with a 3.0 V6 automatic transmission always overheats on hills. Anytime we are climbing a hill it gets too warm, going downhill it cools off again.? It also heats up when you are pushing the engine, going fast on level ground, even on cool day. The gauge is nudging the red zone. So far, I have replaced the three-row radiator, the thermostat and the fan clutch.? I've even removed the front license plate. It was blocking a small air supply slot in the bumper. None of this has helped.? When I replaced the thermostat, I expected sludge, but the port and the thermostat was clean as a whistle. I intend to flush the system, but it seems very clean already.? I'm contemplating replacing the water pump (huge job). The pump doesn't leak, and the bearing seems sound (no play). Is this a common problem with the V6 engines or am I missing something? Has anyone else had this problem and if so, how did you solve it?

Jeff Cardinal


--
Chuck Bridges
 

Your symptom of overheating at high speeds or on hills indicates the overheating problem occurs under high load/high RPM.
?
The causes of this generally fall into one of two categories:
?
1) An issue with the cooling system not allowing it to dissipate enough heat. Given your observations and the
repairs you've already tried, this seems unlikely.
?
2) An issue with the engine causing it to generate more heat than it's supposed to, and the cooling system can't keep
up the above-normal heat load.
?
The most likely reasons your engine would run hotter than normal are running too lean (not enough fuel/too much air),
improper ignition timing, or poor exhaust flow. It's possible you might have a small head gasket failure allowing exhaust
to push into the engine water jacket, but that usually wouldn't be load-dependent.
?
If I had to take a wild-a** guess, a restricted exhaust is the most likely culprit. Another commenter he fixed the same issue
by replacing the catalytic converter. You can have a mechanic test it by putting an exhaust backpressure gauge in place
of the oxygen sensor. Or he can check the temperature difference across the inlet and outlet of the converter. If the temperature
doesn't change then the coverter is not working and is likely partly clogged.
?
Good luck,
?
Buzz L.
San Jose, CA
Former '86 Dolphin 500, '89 HiLux Longbed, and '96 Tacoma owner
 

I can see how a clogged cat converter ( exhaust backpressure ) could cause over heating?
but I cannot agree that a new converter would be better than a straight pipe in reducing
the back pressure and fixing an overheating problem.? ?Tell us again .... did you actually?
put a straight pipe in before a new cat converter installation ?? ? However I might agree if
the engine computer can somehow sense exhaust pressures or temperatures? and make a correction to?gas mixture ratios that would cause extra? heat.?
 

Yes, I tried an actual straight pipe after the O2 sensor. Even replaced the O2 sensor. Tried cleaning the old catalytic converter (foolish idea). As soon as I put on the new converter everything was fine. I’m not mechanical enough to explain why it worked for me but in my case it did.

On Sun, Mar 16, 2025 at 11:18?AM Scott Perkins via <2scott=[email protected]> wrote:
I can see how a clogged cat converter ( exhaust backpressure ) could cause over heating?
but I cannot agree that a new converter would be better than a straight pipe in reducing
the back pressure and fixing an overheating problem.? ?Tell us again .... did you actually?
put a straight pipe in before a new cat converter installation ?? ? However I might agree if
the engine computer can somehow sense exhaust pressures or temperatures? and make a correction to?gas mixture ratios that would cause extra? heat.?


--
Chuck Bridges

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