Thermostat Problems

[sdbraverman]

Hello,
I'm new here to this forum. I have a 1999 suburban with a 6.5 and 135k miles. I have replaced my thermostats three times in the last year. The truck runs too cold.

The first time, I used NAPA stats. They were okay for about six months, then the engine temp dropped, and it eventually tripped a code for too cold temp. I ordered AC Delco 195 stats, and it ran perfectly at 195 for about a week, then started to run cold again. According to my scan tool, 145-150 degrees.

Last week, I installed another pair of AC Delco 195 thermostats. At first it was nice and warm at 190-195, but today it wouldn't go over 180. Today's ambient temp was 45.

What is going on?

[DennisG01]

I'm not an expert, but I wonder if there is dirt/crap/sediment in the cooling system and it's causing the stats to stay open (not fully close)? Have you had the system thoroughly flushed? Including the rear lines, as well?

[AKMark]

What are your current outdoor temps?

My 6.5 needed a grill cover when temps dropped much below 35F to be efficient.

When it's -25 or colder, the old 6.5 barely warmed up at all, even with the cover unless I was towing something.

[rustyk]

I'd suspect the temp sender as well. It's odd for that many pairs of 'stats to fail

[Dvldog8793]

Howdy
What is your heater output? If your heater is blowing nice hot air then I would suspect the temp sender.

Otherwise the dirt chunk theory sounds like a winner.

FWIW....My truck only runs at about 175 in the winter months, but I have never set any codes.