Poor mileage - Thermostat ???

**kjb13** · 10-16-2009, 10:12 PM

The last few tanks seem to be really bad mileage. I just realized that my temp. gauge is reading about 160. I'm guessing the thermostat is stuck open. Could this be the reason for the bad mileage?? If so, what thermostat do you guys and gals recommend??

Thanks,
Kevin

**unplugged** · 10-16-2009, 10:13 PM

Not usually, but it depends on what you are driving.

Give us a clue please.

**kjb13** · 10-16-2009, 10:16 PM

Sorry. 1997 Silverado, extended cab, 4x4, 350, auto., 110,000 miles.

**kjb13** · 10-16-2009, 11:14 PM

Any ideas??

**vncj96** · 10-16-2009, 11:15 PM

Yes a non working t-stat can effect your mileage. When your engine is running cooler without the computer tuned or a programmer that can change it, it reads cooler so it dumps more fuel in, now if you had it adjusted to take that extra fuel it would be fine, but without that it just has too much fuel, I would bet you have some black smoke coning out the tailpipe.

**unplugged** · 10-16-2009, 11:33 PM

Originally Posted by kjb13

Sorry. 1997 Silverado, extended cab, 4x4, 350, auto., 110,000 miles.

Welcome. Check out how to include info in your signature here: GMTC

The stock temp is a 195 deg. tstat. The emission control system is temperature dependent. During the summer I run a 160 in my burb just to get a head start on the 100+ temps here in the Mojave. In the winter I'll swap out to the 195 just so she warms up for the cold mornings.

It's cheap enough to change the tstat. You can also test it, by dropping it in a pot of boiling water. (CAUTION do not use the little woman's favorite quart sauce pan, or you may find out what a frying pan upside the head feels like.)

I'd look into something else like a fouled plug, loose plug wire. Check for DTC codes just in case.

And don't forget the often overlooked tire pressure.

From: 2carpros.com
The engine's combustion chamber can reach temperatures of up to four thousand five hundred degrees Fahrenheit. About thirty percent of the fuel is converted into actual power, and about seventy percent is spent into heat. A cooling system protects an engine from damage by transferring heat to the atmosphere by using the radiator. A correct operating temperature is critical for the proper function of the engine. The thermostat controls when coolant is allowed to flow into the radiator and back into the engine. Manufacturers have found that a 195 degree thermostat is optimum for efficiency. Below this threshold the catalytic converter will not work to capacity and will produce increased emissions. ..............