[bhill86]

The Pontiac 400 in my 77 trans am currently has a 180° t-stat in it, aluminum water pump with cast impeller, and 4 core radiator in front of an HD thermal clutch on a 7 blade fan. Never had any overheating issues with it generally though it does warm up a little in the dead of summer with the A/C on at idle after a few minutes. Runs under 185° all day long otherwise. Even with A/C on. Warmer on the eway, cooler on city streets.

On the flip side, with ambient temps only being 36° today, the engine only got up to maybe 160° on the e-way and on city streets was maybe 140-150. I feel like this is too cool. Do you agree? If so, any thoughts? Don’t particularly want to swap thermostats upon the season changes.

[Vroom_vroom]

It’s not going to matter on your thermostat temp. The cold weather cools the giant mass of coolant in the radiator and there isn’t enough heat being put off by the motor to compensate so the temp drops.

I have the same set up with the same problem.

115 in the summer with me being full stupid it never budges over 180 even in stop and go. It has a lot of reserve cooling capacity. Put a piece of card board over the radiator in the winter and problem will be solved.


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[bhill86]

Fair enough, thanks.

[kingbuzzo]

or a beer case like we did back in the day...lol

[70GS455]

Sounds like your thermostat is faulty, staying partially open when it should be closed while the coolant is under the set point. Not a hard task to replace one but won't really cause any problems, other than the oil not getting hot enough to evaporate any moisture. But with very few miles driven over the winter, shouldn't be a problem

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[Goatracer1]

I agree with 70GS455. Doesn't matter whether you have a small radiator or large. Until the coolant reaches the temp rating (give or take 5 degrees) of the thermostat. the rad will have no effect on engine temp. The water will just circulate around and around the inside of the engine. Chances are your thermostat has been open all summer.

[bhill86]

Easy enough to double check I guess. I put the 180° in a couple years ago I think it was.

[dataway]

X2 on the thermostat, a leaking thermostat and having the interior heat on could keep temps down like that.

[bhill86]

I never took note before but now that you all mention it, the engine does just gradually warm up to a point as opposed to what I’m used to with other vehicles being a warm up till the thermostat opens then a slight fall back.

[JLMounce]

Had the same issue last winter, couldn't get the car over 130 in temps 40 degrees and cooler. Did some top end maintenance in the spring and discovered that the T-Stat had completely fallen apart. It was essentially nothing more than a very slight restriction.

Had a Mr. Gasket High Flow 180 degree unit in it. Replaced with a Stant 180 degree unit.

[Vroom_vroom]

Dunno about the op but I have a super stant 180 and can sit there with my ir gun on the thermostat housing and watch the temp fluctuations as it opens and closes.


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[dataway]

Keep in mind on our Pontiacs the thermostats spend a lot of time wide open So not altogether surprising they might stick open a bit after a few years.

[lust4speed]

If you followed the recommendation of drilling a hole or two in the thermostat to insure against trapping air in the system on initial fill it will come back and bite you in the winter. Been there, done that, and I don't anymore.

[68 Firebird]

Lust is right. Any hole at lower temps with aluminum rad has same results.
Also have tweaked my cooling system to perfection and yes with mod thermostat
It does same. I have a summer and winter stat for years.
Now I’m lazy and just leave a 170 in all year.
Gerry

[bhill86]

Hopefully this is as simple as a stuck thermostat for me. Wish I’d thought about it when I had everything drained and the engine out but oh well. I’m really curious to see if this is all it is.

[chuckies76ta]

Yes like mentioned, I'd change the stat. A 180 thermostat is designed to bring the engine up to 180 before opening. Not 140-150. You only need to drain coolant down below the return holes in the water pump. and really not even that low. Has to drop below crossover. Here a little trick. Before installing new stat fill radiator slowly till you see coolant coming back into crossover. This will allow any trapped air in the heads to purge out. Get yourself a nice stainless thermostat from Napa. And never push on the bellows of the thermostat as it wrecks it. Something else that's a learning experience is a pot of hot water and thermostat and check it at the 180-185 degrees in the hot water.. Use of a kettle help with water temp.

[bhill86]

Thanks I appreciate it

[bhill86]

Grabbed a new 180° thermostat today. Early observations aren’t ideal. I tested both the new and old thermostats in boiling water. Both were closed to begin with and opened around 180°. I put the new one in and ran the car as long as I was able before I had to leave for work which was prob 10ish minutes. Maybe a bit longer. Todays temps were around 45° ambient and the engine seemed to level out around 150° before I ran out of time.

One thing I plan to check is whether or not the thermostat is getting sandwiched between the water neck and intake or if it’s lifting under pressure and coolant is sneaking by. (Im using a chrome water neck with a rubber o-ringtone seal, not a stocker) I don’t think that’s the case though. I was able to hold the upper radiator hose with my hand and it wasn’t hot. 30s for a high the next several days so I’ll have to go for a drive when I have time.

I guess there are worse issues to have.

[chuckies76ta]

Well it's good you checked them to see what is going on. The engine should have came up to 180* Now you know something isn't right. Maybe it might take a bit longer to heat up.. Hmmm. I ran my IA2 block today with a 160* stat and it opens a 160-165. I left the electric fans off and watched the temp gauge rise onward to 170-185. At 185 my sensor in the coolant turns the fans on automatically. But at around 160 * I could feel the inlet on the Radiator getting hot. What are you using for a temperature gauge?

[bhill86]

Have the factory gauge and a no-name mechanical gauge currently hooked up. I’ve compared that against the crossover/water neck temp with an IR thermometer and also previously had an autometer (I think it was) mechanical temp gauge installed so between comparing them all I feel fairly confident the temp I’m seeing on the no-name is accurate.