Thread: Very weird engine temperature behavior...

Recently I removed my 180* T-stat for gas mileage purposes (stock car). I had used the 180 as a replacement for a 195 stat that was running below 170, thinking I'll need the 180 soon. Anyway, I took that one out and put in a new Stant 195 thermostat and this is what I'm getting:

Temp will warm up like normal to around the 195* range (just before the middle of the gauge), then the t-stat opens and the temp comes down to around 180 - normal, right? Well, it never gets back up to 195. It just fluctuates around 180. This happened yesterday and today. If I sit in the driveway the temp will come up past 195 until the fans come on like it should. The problem only occurs if I'm moving. It's been 50 deg outside where I live.

Yesterday I sat in the driveway and held the car at 2500 RPM until the temp was 210 for about 5 minutes, just to flush out any possible crud sticking between the thermostat plunger and the flange, thinking something got caught as it was shutting. Then, this morning, same problem. All my readings are just coming from the gauge... currently looking for a used scanner.

Any thoughts? Did I get a bad t-stat?

Originally Posted by Bio248

that fans are turning on in the range for a 180* thermostat.

What do you mean? The PCM is stock.

Today on the way home from work it only got to 190 before coming back down to 180. I'm thinking the stat may be crap.

Fill process:
Filled coolant w/ bleed screw off, started engine, topped off rad, closed bleed screw, closed cap, ran to temp, turned off engine. Made sure overflow was full enough (went down a lot during cool-down) then topped off rad and overflow again after engine cooled.

I just went out and squeezed the upper rad hose with the bleed screw off and coolant immediately came out (no air space). I've run it constant at 210 in the driveway, so I'm assuming any air has been pushed out.

I guess next step is replacing the thermostat. Anyone else have a problem like this with a new t-stat?

Originally Posted by scottydoggs

when you bleed it, you need to run the car till its hot with the rad cap off, and wait till the t-stat has opened up, open the brass screw, don't remove it, 2 or 3 turns, it will blow bubbles if it has air in it, when a steady stream of coolant comes out shut the screw, then top off the rad, and cap it. oh and put a 195 t-stat in it if you swapped it back to a 180, your not tuned for a 180 and you don't need it.

Exactly. I realized I wouldn't tune for a while, so I have the 195 in there now - this is the one giving me problems.

Also, whenever I try to let it run with the cap off, the coolant comes up too fast and I have to put the cap on to keep it from pouring out. I can try letting some coolant out and doing this, but wouldn't running it above the t-stat temp flush all the air out to the rad? I mean, 10 mins at 210, all the air will blow out and collect in the rad one way or another. Right?

That's what I did and I'm assuming I got all the air out, albeit not the common way. I can see how a pocket could get trapped in the upper rad hose, but I just checked for that and the coolant was right up to the bleed screw.

I agree. The gauge is mostly crap. But in this case, I don't think it's the problem since I can sit in the driveway (with no airflow over the rad) and the temp does what it should - and the fans come on right near where they should, just using the gauge reading.

However, a scan gauge is high atop my priority list.

Any comments on Stant as far as quality?

Today on the way to work it didn't break 180. Now it just warms to 180 and stays there like I have a 180 in there...