Thermostat = Bad Mileage

[Mishney]

I have read a few posts here that say a stuck thermostat can lead to poor gas mileage. Is this true? Has anyone actually experienced it. Only reason I ask is when I first got my SHO I would get 300-350 miles per tank easy. Now Im lucky to get 300 if I push it. It also takes forever to heat up on cold days and the heater also takes forever to push heat. Im thinking the heat problem is the thermostat but could it really help gas mileage or is there another major factor to gas mileage other than driving style?

-Matt

 

[AutoXSHO]

Yes, if the thermostat is stuck and the car overcools, the fuel mileage will go down. When cars are cold the A/F mixture is adjusted more rich.

John V

 

[sdpatt]

If the needle does not rise into the NORMAL range your thermostat may very well not be fully closing. When the needle is below the lower tick mark in the NORMAL range, the engine control is inthe "open loop" mode which does not use the inputs from all of the various temperature, pressure and oxygen sensors. Since the engine is still in the warm-up mode, the fuel mixture is richer than optimal for performance, emissions and fuel economy. I can only get 300+ miles to the 1/8 tank mark (about 14 gallons used = LOW FUEL), or > 22 mpg, on the open highway. Around town it is in the 225-280 mile range, or 16-20 mpg. Your mileage depends very much on your driving style.

 

[SilverSHO]

A stuck thermostat can lead to poor MPG, but not always. Replacing the T-stat in my car did nothing to affect my gas mileage either way, which leads me to believe there was nothing wrong with the old thermostat, aside from maybe having it installed wrong. The new one went in correctly, though.