Question for you car guys

I have a 2000 Buick Centry 3.1 V6. Bought the car new.
Lately the fuel milage has fallen in the toilet.
This car used to average mid 20’s mpg.
Now I’m getting closer to 12 mpg.
The car runs great, no misses, no leaks, no lights on.
Would an oxygen sensor or mass fuel sensor cause this?
Seems to me the computer thinks it needs to be in a rich fuel setting all the time? Any help is always appriciated.

might be engine seals

Have you stopped by a Autozone or equivilant store to have the computer chip read? You may have a failure that isn’t triggering the check engine light. If there is a registered error code present, that will save you a lot of blind trouble shooting

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might be engine seals

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I agree with this. Our 2000 grand prix had leaks around the intake and the MPG dropped like an anchor

An oxygen could cause it but I would lean more toward a faulty temp sensor; if the computer is reading an incorrect resistance at the sensor, it may think the engine is always cold. It would then compensate by dumping more fuel in trying the get it to warm-up.
Just my .02,

Don

Since I had no lights on, I didn’t think there would be any codes to read. I will stop in and check for any codes.
You’d think with intake gasket issues, I’d see coolant in the oil or have fluxuating water temps. This car only has 50k on i.

have your fuel filter and air cleaner changed and report back.

yes the intake gaskets are a issue but ,I would do fuel filter 1st.

Are you losing any coolant at all?

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Since I had no lights on, I didn’t think there would be any codes to read. I will stop in and check for any codes.
You’d think with intake gasket issues, I’d see coolant in the oil or have fluxuating water temps. This car only has 50k on i.

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we only had about 65K on the grand prix when it fell off the cliff

I had a 2001 Buick Regal with the same problem, turns out the catalytic converter had collapsed inside, a common problem for a few years, which I discovered was covered under warranty up until 100k,check with a dealer, mine was repaired in 2 hours at no cost. Good luck.

Thanks for the replies gentlemen