86TpiTransAm

Ok so I'm having a little problem with my car running a little warmer than it should be. It's a 1991 Firebird with the V6. I bought the car from the original owner a few months back and it was very well taken care of. I noticed it did use(leak) a little antifreeze though and soon found out that it was leaking from the heater control valve next to the alternator. A few weeks ago I replaced that valve. I noticed there is still a very very small spot under my car where it's leaking antifreeze somewhere else. Not big enough to freak out about. Last night I was on my way home, cruising down the highway and the temp guage starting rising and got to about 230 before starting to back down. Now keep in mind it was about 25 degrees out when this happened. So I checked the antifreeze and sure enough it was a little low. So I topped off the fluids. Problem is, the problem hasn't gone away. The car typically would run around 185-190 on the guage when I bought it in August but then started running about 195-200 a month or so ago... and now this. The engine isn't overheating but it's definitely running warmer than I would like it to. I have a suspicion about the cooling fan but it doesn't make sense to me because if it were the cooling fan then the engine should still be cooling just fine on the highway and it's not. I checked the air deflector under the radiator as well and it's still in place where it should be so that's not it. I don't seen any visible signs of leaking antifreeze at the weep hole of the water pump and I don't get the typical signs of a leaking heater core either so I don't think that's it either. Sticking thermostat has crossed my mind as a possible culprit however.

If anyone has any suggestions on what to check next or where to go with this, it would be greatly appreciated. As soon as I get home today I will be hooking up my auto x-ray to check the readings from the coolant temp sensor and then I'll go from there.

TIA!

rgarcia63

I doubt that the Temp Gauge and The CTS are reading the same temp, but it's the CTS that the ECM depends on for it's temp data, which is used for; among other things, turning on the fan.

At 230°F the primary fan should be on, the secondary if you have one will turn on at 238°F.

If you can get the temp gauge to read 230 and then quickly measure the resistance across the CTS terminals (CTS is in front of Intake 2-wire connector; yellow & black wires.)

If the resistance is 185 ohms then the actual coolant temperature is 210°F.
Less resistance is hotter.
More resistance is cooler
450-185 ohms is 160 to 210°F
Temp versus resistance is inversely proportional, but not linear.

86TpiTransAm

I hooked up the Auto X-ray and the CTS is only reading about 5 degrees less than the temp guage. I still don't think the fan is the problem because if it were the fan then the car should be cooling fine on the highway with the air hitting the radiator and it's not.

I picked up a new thermostat today and tomorrow I'm going to tackle that project and see if it solves the problem.

rgarcia63

I'd fix that small leak before doing anything else besides changing the T-stat.
Leaks make me lose sleep, can't relax until it's fixed.

Post the results of changing the T-stat, please.

86TpiTransAm

Finally got the thermostat changed. Took about 4 hours but we did alot of other things besides changing the thermostat and changing the tstat on this V6 is NOTHING like changing one on my '86 TPI engine. Had to make a couple trips to the parts store as well. Had to get some clamps to replace the crappy factory hose clamps and also replaced the two small hoses coming off the bottom of the throttle body to a junction that goes into the intake.

Took care of the problem though. Looked like the original 15 year old thermostat even. You could push it open with your fingers without any effort at all. The car was very well taken care of by the original owner, who I bought the car off of back in August, but it appears that they didn't change anything that didn't need to be changed.

It definitely took care of the cooling problem and I think I took care of the coolant leak in the process but I'm not too sure just yet. I'll know better in the next couple days. I "think" it was leaking from this coolant junction point just below the throttle body. For you non-V6 people, there's a metal junction point just below the throttle body with 3 metal coolant lines coming off it and it has a big connecor with a plastic quick disconnect which snaps into a fitting on the intake. I believe the o-ring was allowing a small leak out that connector so I replaced it and the plastic quick disconnect which was broken as well.