Low temperature (sometimes)

[gr_diver]

Hi everyone!

To keep the post short, the last few days I have an issue with my car's engine temperature. It warms-up normally, and if I keep driving at city conditions everything is well. If though I take it on the highway and drive for a little time, when I later get out of the highway and drive at regular speeds, the temperature drops below normal... It had done it once about a month ago, but it came back yesterday and today...

Does it sound like a thermostat that when it opens to the full extent of it's motion gets stuck there? And maybe during normal open/close cycles, that it does not reach fully open position it works good?

The cooling system worked very well prior to this. The needle during city driving stayed (and stays) right below the middle, during highway it went (and goes) exactly to the middle, and if I went in city after highway, within 2-3 minutes the temp would drop to it's normal again, without climbing not even a bit... Fan shroud in place, 50/50 ethylene glycol coolant, stock thermostat (87*C), 5-blade stock fan.

I think it is an actual temperature problem, because yesterday that I was using the heater it happened more pronounced (needle almost touched the blue zone), and because the fuel gauge works normally (voltage stabilizer out of the picture).

[tekenaar]

More than likely, stuck (or sticking) open T-stat. When you're in city traffic, stop-and-go, not as much air flows through the radiator to cool the fluid, so a bit higher temp is shown on the gauge. When on highway, lots of airflow through radiator, temp drops. The kicker here is that it's "lower than normal" with the heater on . . . think of it as adding another radiator in the coolant circuit! Bet you're not getting much heat from your heater, are you!

Replace T-stat . . .

[gr_diver]

Funny thing is, while I am on the highway, the temperature is normal. Get out of the highway and after a minute it slowly starts to fall...

During the past winter months, when everything was ok, I had good heat coming from the heater. I hadn't used the heater in a while since the weather is very nice the past month or so, and yesterday I used the blower in HOT to defog the front glasses... I can't say for sure if it was hot or not...

I have another t-stat. I'll drop it in tomorrow and see how it goes...

[gr_diver]

It's been since Monday I 've been struggling to find a t-stat that works as it should. At first I bought a genuine GM part (made by Wahler), it was mulfunctioning, opening late (seen from the dash gauge). I got an identical replacement, together with another one aftermarket made by Effbe. Both were mulfunctioning, opening late (again by the dash gauge). I got so angry that I bought another t-stat, identical to the old one, from another dealer. This one was made by Calorstat. I also bought a digital probe thermometer to test all of the new, plus a few more good used units I have (that were replaced when other things were the actual problem), to determine whether my gauge is showing correct temperatures.

Results:

GM genuine (Wahler, 87*C/188*F), new: opened at 96*C/205*F
GM genuine (Wahler, 87*C/188*F), new: opened at 93*C/200*F
Effbe (88*C/190*F), new: opened at 94*C/201*F
Effbe (82*C/180*F), used: opened at 89*C/192*F
Calorstat (82*C/180*F), used: opened at 83*C/181*F
Calorstat (88*C/190*F), used: opened at 88*C/190*F (this was the sticky unit I replaced)
Calorstat (88*C/190*F), new: opened at 88*C/190*F

From now on, only Calorstat units will go in there. They all were opening correctly or within acceptable range (1*C max variation), and they were fully open at 100*C/212*F. The faulty unit opened correctly, but was slow to respond when cooling, it re-closed at 80*C/176*F, that's why I had normal warm-up, but underheating later. All other units were opening too late, and were not even fully open at 100*C/212*F. In addition only the Calorstat units have the air-pocket purge "thingy".

I posted these for reference, and I can post pictures if you want, to see what to avoid...

Now a question. Together with the new Calorstat t-stat, I was given a rubber gasket ring to fit around it's periphery (pic). Have you seen these again? I hadn't. Do you think it would be of benefit to use it? The guy said that it goes together with the paper gasket, it does not replace it... I can't see though how the paper would seal above the rubber... Maybe it is supposed to be used on it's own, as it looks like it fits the recesses that the t-stat housing parts have. Or maybe they are used in other models, as these t-stats were common in as late as '92 Opel models (Corsa).

[gr_diver]

Ok, the question about the rubber gasket was self-answered the moment I tried to test fit it. The cover would not close with it used...

[gr_diver]

Ok, I had enough of this t-stat thing. I spent the last 15 days, trying to find a t-stat that works as it should, I finally did after I replaced 3 or 4 of them. After a week of good operation, yesterday I thought it is time to finally fix that tiny little leak it always had from between the t-stat housing and it's cover. I took the whole t-stat housing assembly out, miled the mating surfaces flat because the cover was a tiny bit warped (that's why it slightly leaked), cleaned them inside out, and today I reassembled with new gaskets etc, everything in like-new condition... Static leak test = good. Short test drive = good. Being under pressure for about 2 hours afterwards = good. So I took a nap, and went out for a beer. During coming home afterwards...

...GUESS WHAT HAPPENED? The stupid new t-stat stuck open

That's it. Where did my dad put that shotgun? It must be somewhere in the basement...

[ronskydivepops]

You must have a Gremlin living in your cooling system. Instead of you having a beer! Maybe you should give one to the Gremlin..

[gr_diver]

Yes, and it must be living between the head and the t-stat housing, because it had not been bothered by me opening the cover to change t-stats. Only when I removed the housing from the head did it get pissed. I think it went ahead and put a stick in my t-stat when it was opened, that's why it wouldn't close again.

Now what color of a gun do I need for cooling system Gremlins? It must be the green one right?

I should have known it was in there, when I took the housing off a funny (bad) smell came from the inside of the head. It must be it's toilet there...

[gr_diver]

With a stone cold engine there was minimal coolant circulation in the radiator, so I once again removed the t-stat. The gremlin had taken a $#1+ in revenge, and the "product" got stuck between the mating surfaces of the t-stat's valve, holding it just a little tad open, about 1 mm. I cleaned it and checked it for proper operation, looks good. So I went ahead, I apologized to the little creature and promised not to bother it again, and reinstalled the t-stat. Maybe it will forgive me, and the two of us can live peacefully together for a long time again...