tstat diagnose
 

Hey All,
99 Blazer, 300k, well maintained.
I noticed lower fuel mileage this winter and engine temp is a bit lower.
I suspect tstat might need replacing but want to verify some live data readings first.

Tstat is 195 version. While on a recent road trip (ambient air temp was mid 20s), I monitored live data with my scanner and the highest temp recorded was 183.
In your experience, should a correctly functioning tstat run 10-12 degrees below stated temp? Or is the lower reading caused by the colder ambient air?

Thanks

I've got a 195 in mine, and it usually runs around 187 or so when live data is viewed

Ok. thanks for info. I guess the colder temp would account for the lower temp reading I'm getting.

Personally I wouldn't worry about 183°. Maybe a little on the low end, but not enough to warrant yanking the stat out.

If you wanted, you could pull it, and boil it in a pot of water on the stove, and monitor the temp you see it open at with a thermometer. Free way to tell if it's working or not, you're just out the time, and some coolant

It sounds like it might be starting to stick a little. At 183 it's probably not a big deal unless reduced mpg and/or lower heat in the climate vents start to annoy you.

OK, thanks for the info guys.
I looked thru my log and it is 8 yrs old, so I will add it (along with coolant flush) to my list of maintenance items to do when warmer weather arrives to the midwest.

Presumably you'd change the thermostat when flushing the coolant, and Dex-Cool (assuming that's what you're still using) is only rated for 5 years. Dex-Cool is basically safe if maintained but doesn't tolerate neglect well and the corrosion inhibitors break down. If it's been 8 years I'd want to thoroughly flush as soon as possible and probably even run some Prestone radiator flush through it first.

As soon as you get a couple days above freezing I'd jump on it. A sticking thermostat might be the least of your problems.

Yep, got rid of the dex-cool 8 years ago, with a thorough flush with prestone, then replaced radiator, hoses, tstat and refilled with green antifreeze and distilled water.
The coolant was changed 5 yrs ago when the LIM gasket blew and had to be changed. As it has been 5 yrs, I will probably flush and replace tstat at that time.

I assume you've been using the heater? That might take enough heat from the engine to account for the lower temperature, too.

Oh. Well perfect timing then. :)