Thermostat Getting Lazy.

[George7941]

When the thermostat is fully functional, the coolant temp is at a rock steady 90*C on the ScanGauge. However, now the temp fluctuates slowly, over the course of a few minutes, and rhythmically between 89 and 92. Time to replace the stat.

Dunno why the stats don't last very long on this truck. The OE GM stat only lasted a couple of years and then started opening early, so that the engine was running at 80C. The replacement Delco stat from RockAuto (did not bother with the warranty, don't like a dealer mechanic of unknown competence messing with my truck, did it myself) lasted for about three years and then started opening early, exactly like the GM. I got tired of GM/Delco and went with a Stant Superstat, from RockAuto, next. That lasted for a few years and is now on its way out. Coolant is Dexcool, see no need to switch. Cooling system has had one distilled water flush so far.

Luckily the stat is super accessible and super easy to change out on my truck.

 

[xxch4osxx]

I never replaced the thermostat on my Silverado but it was the 4.8 engine. It always was steady at holding the temp as well judging by my Scangauge.

 

[mrsilv04]

A thermostat is the only thing that I'll buy directly from the dealer. The "Delco" stat that you got may have been exactly that.

A part branded as ACDelco doesn't always equal OEM.

 

[George7941]

Just checked RockAuto, the 4.8 uses a different stat. Maybe it is only the 4.3 stat that is troubleprone, maybe it has been just the luck of the draw for me.

 

[George7941]

True, but the OE GM only lasted for a couple of years, so that is why I eventually switched to Stant.

 

[GMBoy]

2006 sierra 6.0L the thermostat never failed. I finally changed it out at 115k just because I was doing all the hoses and belts along with a coolant flush. Used AC Delco replacement off rockauto.

 

[Nick1994]

I wouldn't use a Stant. My grandmothers Chevy Trailblazer was having overheating issues after the thermostat was replaced, OE was stuck open. The Stant's opening was over 10% smaller than an OEM (I measured with a micrometer). I had them side by side and the Stant is night and day smaller. Runs a lot cooler with the OEM thermostat.

 

[splinter]

Originally Posted By: George7941
..over the course of a few minutes, and rhythmically between 89 and 92..

Reads like entirely 'normal' temperature regulation hysteresis in my vehicles, particularly during cooler weather.

Have you found its cold start time-to-temp longer than during previous scan sessions during similar ambient and operational conditions?

 

[George7941]

The warm up time hasn't lengthened and it is not a big issue and I might not change the stat for a few months.

But the hysteresis leading to this 3 degree variation isn't normally present, so the stat is not reacting as quickly as it should. Previously, the only time the temperature climbed above 90 was at the end of warm up when the temp reached 90 for the first time, there would be a little overshoot to 91 or 92. then a little overcorrection to 88 or 87 and then the temp would settle in at a steady 90.

If it were not for the ScanGauge, there would be no indication of this laziness of the stat. Certainly it does not show up on the dash temperature gauge. There must be lots of cars with somewhat lazy stats whose drivers are not aware of the situation. Stats only get replaced when there is a major malfunction.

 

[splinter]

^ Yeah my data logging shows how dramatically damped the OE gauges are in our GMC.

You're certainly correct, though (too), that non-car commoners only think of their cooling systems
when the heater isn't working or there's steam coming out from under the hood!

 

[Colt45ws]

Yeah, I find that about 3 or 4 years is good life for a stat. I did a bunch of work to a friend's 2010 CVLX and put a water pump in it (it was leaking). Then find out it was only running 170-175F. Kicked myself for not ordering a thermostat with the pump. Ended up doing so much work to his car though it didnt even matter. Got a new stat in and it was running 188-190F, like it should.