DaveInSaltLake

When it was cold here in Salt Lake (<30F) my 'around town' mileage decreased from the normal 23 mpg (per the onboard computer) to around 15 mpg.

It bothered me, but the car wasn't showing any codes (O2 sensors) and I didn't have the time to dig into it. I just assumed it was the winter grade gas and thought maybe I needed a tune up.

But now that the temps have been regularly > 40F, the mileage is back up to normal.

Does anyone else experience a fluctuation of this magnitude? Possible causes?

audijim113

I've seeen a lot of thermostat problems where it would not warm up. With the engine running too cold, the computer thinks it needs the cold start and it runs rich.

Other than that, i'd check the vacuum hoses and look for the other "usual suspects". however, you'd notice a rough idle if you had a leak.

DaveInSaltLake

Yes, the temp seemed normal. I'll keep a closer eye on that the next time the temp drops.

Strange how the mileage rebounded when the outside air temps warmed....