Ok, I have a problem which I've never encountered before...

Is it possible that a thermostat could get lazy? My truck will get up to about 95C (about 205F) on the first cycle only, then dips down to mid hash mark between dead cold and 12 o'clock (I would assume by splitting the difference it would be 70C or 160F).

When I say the first cycle, I mean start the truck from dead cold sitting overnight. Driving it for a bit it will get to 95C, hover there for a few seconds, then drop rapidly to 70C. After it drops down, it moves up or down from that point a few degrees ~5C +/-, but never reaches 95C again.

If I park it for a few hours in this cold weather, it will get up to 95C once, then revert back to 70C.

I really noticed it the other morning coming home from work. There was a heavy freezing drizzle falling, and my defogger could not keep up. My windshield kept freezing up. My temp gauge was below 70C, I would guess it was around 50-60C. The air coming from the vents was lukewarm at best.

I also noticed that the truck was a pig on gas for the trip. Now I understand that colder temps use more fuel, but this particular morning, it was warmer than it had been in two weeks. My fuel consumption was never this high.

I want to just change the thermostat, but living in the sticks, the nearest parts store is almost an hour away. If someone has any insight if there are more problems involved, then I can source parts while I'm there.

 

Just broke down and went and got a new tstat... I bought plugs wires rotor and cap to not have it a wasted trip.

So far looks like the temp is sitting a little higher, but tonight will be the test on a longer drive. The tstat that I pulled will be tested tomorrow. I suspect a colder range was used.

 

Might be an air pocket trapped in the cooling system. Raise the right front corner of the vehicle, remove the radiator cap, hold RPM ~2500 and keep adding coolant to keep it full. While the cap is off, rev the engine a few times to help move the air pocket. When/if you let it idle with the cap off, coolant will push back out, try to avoid that by putting the cap back on BEFORE you let it idle. Stat needs to be 195F, and it should regulate very close to 200F. The temp should be stamped on the stat somewhere. It indicates the temp that the stat begins to open, (not the regulated temp).


I hope you installed AC Delco plugs, cap, & rotor Very important on this engine.


Keep us posted.

 

The new tstat is a 195. The old one had no markings regarding temps on it at all. But it did open well before water was at a boil, so either weakened spring, or colder range. Either way, the heat is very nice now, and my windscreen doesn't freeze up anymore. Temps aren't sitting at 12 o'clock, but in between 70C and 100C, so lets just say 85? But regular air temps here have been in the range of -15C to -25C :O

And of course I have all ac delco parts. I didn't buy the platinum plugs though, I prefer the good old copper plugs. Never had problems with the copper plugs yet.