Stuck Thermostat causing TC to not look up? [Archive] - Forum


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03-01-2005, 03:34 PM
Ok so I have had a thermostat stuck open for about 4 months now (haven't done anything about it since it is overcooling). Well the car throws a P0128 code about 1 a month or so and I just clear it out of the computer with the scan tool I have. But hears my question: I read on hear somewhere that if the PCM reads some types of codes in the computer it will not let the torque converter lock up.

I have been feeling my car do what i would consider to be a slipping TC for about 2 week now. It seems to accelerate just fine from a stop until you get around 4000 RPM's or so and then it becomes very sluggish and doesnít want to accelerate anymore and wont shift till you let off the gas a little bit. Also when i am on the highway and have cruise set to 70 or 75 it will be fine when on flat surfaces but as soon as it is on any kind of hill it will gear hunt back and forth from overdrive to 4th until i just get on the gas and then it will stay in 4th but not want to accelerate any no matter how mush on the gas to push until it shifts to 3rd and then will slowly accelerate (just enough to even see the speedometer move).

Anybody know if the PCM is causing this because the computer is telling it that my coolant if cold. On a normal day the coolant stays around 160-170 since the thermostat is stuck open and the water pump runs constantly.

I plan on having the thermostat fixed here in about a week or so, so i guess i could see if that helps the problem once i get it fixed. I am just worried about the tranny right now; i canít really afford to buy a new one at this time.

Any advice would be great!!!

03-01-2005, 04:47 PM
When my thermostat was stuck on my older car ('89 Century, 3300 - 3spd) the torque converter wouldn't lock up in the winter if it was cold enough out. It would lock if the radiator was warm, but if that cooled off, it would unlock. It was pretty crazy, if I followed close behind a semi, or a big van, bus, etc on the highway, it would warm up enough to lock up. But when the front of the car would get into the windstream after passing, it would cool it off and unlock in after a minute or so. I'm not sure if thats your issue or not, but I wouldn't be at all surprised, because there is a function in the PCM that prevents lockup until things are up to a certain temp. With a cool radiator and engine, you may not be getting warm enough to lock up. Gas mileage is gonna suck too!

03-01-2005, 09:12 PM
yeah tell me about the bad gas mileage. i use to get around 25 or so in the city and now i am at like 19 or so.

03-02-2005, 08:13 PM
my thermostat is messed up to.. except mine lets my engine get up almost 3/4 of the way on the temp gauge. I want to fix it myself but dont know how.

03-02-2005, 09:20 PM
my thermostat is messed up to.. except mine lets my engine get up almost 3/4 of the way on the temp gauge. I want to fix it myself but dont know how.

It's sticking, get it replaced ASAP.
Had that problem on my last car. Fried the tranny fluid. Problem is on an older car that's never had the tranny fluid changed, putting in new fluid can actually be bad. A few months later my tranny wouldn't go into gear the first time I started my car. But after I started it a 2nd time it would work. So instead of spemd $1000-2000 on a new or rebuilt tranny, I bought my GA instead.
BTW last car was an '88 Bonneville.

03-02-2005, 10:29 PM
So would you suggest to get it replaced and change the tranny fluid? I have only 60K on my car.

I want to replace it myself but it seems like its harder than I thought

03-03-2005, 09:44 PM
Most cars suggest 30K mile interval for tranny fluid change. But GM recommends 50K.
I'm not a tranny expert, so I don't know if you're past the point where you'd do more harm than good by changing the fluid. Unfortunately there's no way to tell if your trany fluid has gone bad yet.

I would have them check the trany fluid when you get the thermostat fixed. Personally I wouldn't touch anything in the cooling system. When Dexcool gets contaminated, that's when it can eat away your LIM gasket and then your engine. BTW after I had my LIM leak fixed my water pump went about 2 weeks later.

03-03-2005, 09:53 PM
I myself go for one every two years about 48k kms. It doesn't cost much and can avoid alot of issues or an expensive bill, I so would err on the side of caution.