large mpg drop. 05 vibe gt 130000 miles

[atowley]

Hey giys, i have been tracking my mpg for last year. I have averaged 32mpg up until 6 months ago. Now i am seeing a steady drop and it continues to drop. As seen in my graph. Tuneup done 10000 miles ago with trans gear lube xhanged as well. I live in Mn so we are in winter but I think the drop is excessive even for winter. No check engine light, ideas? O2 sensors maybe? I cant figure out how to attach my picture of graph but its a steady decline from a high of 34 to a low of 27. All in 6 months.

[sideshowalan]

5 MPG less than your 32 MPG average is 15%. A 15% drop in MPG is not strange for winter gas mix.
I wouldn't do anything with that variance unless there were obvious problems, otherwise you're just throwing parts at the car.

It should go back up in the Summer.

[vibrologist]

I agree with Sideshowalan.
Also: It depends a lot how often you start the engine cold. At these wintry temps it takes longer to warm up the engine and transmission which means the air fuel ratio is enriched for longer each time you start the engine cold.

[jayoldschool]

I would do a quick check for a dragging brake caliper. They don't have to seize, they can just get hung up on the mount.

[atowley]

Ok thanks guys!

[circuitsmith]

Another possibility is a sticky thermostat.
An easy test:
Start the engine cold and let it idle.
Feel the radiator hoses as it warms up.
The bottom radiator hose should stay cold until the temp gauge is up to normal.
The top hose might get luke warm.

[BWCAVibe]

I had a similar issue a couple years ago. I do not drive my '04 GT in winter, but in spring I noted a pretty significant drop. I had pulled and cleaned the KN air filter in Fall when winterizing and forgotten to reconnect 2 vacuum tubes at the bottom/back side of the air filter box. No codes were thrown but I "felt" something was off, then noted the mileage drop before I starting poking around a couple weeks later. Good luck.