97 runner. MPG help!

[jacklany]

Hi there.
I own a manual 97 SR5 V6 4runner (115K miles).
Since I bought it, I've had an average of 18.8MPG, but for the past month or so, it dropped significantly, around 11MPG (same tires, same driving).

Possible causes? Could a dirty air filter be responsible for that much of a change?

Thanks.

 

[MikeBoyle]

Dirty air filter and worn spark plugs will cause a noticable drop in fuel mileage.

 

[Duane]

Do you live in a cold state?
Maybe the O2 sensor is weak and not throwing a code.
What does your tail pipe look like...fairly clean and light grey inside or dark colored with deposits collecting?
Is it down on power?/Are cruising engine rpms the same.. ?

 

[jacklany]

Thanks for the cues guys.

The air filter needs a cleaning indeed, have yet to check the spark plugs.

And yes, I live in Montreal, and the MPG dropped around the same time it started snowing and getting cold outside... Power and rpms still the same though, and the tail pipe is clean. I'll check the O2 sensor as well.

Thanks!

 

[d0ubledown]

do you have a foot of snow on your runner when you're experiencing this 11mpg? thats a HUGE drop in mpg. gotta be something else...other than tune up parts. how are you getting your mpg numbers?

 

[grizzlygibbs]

Do they add fuel treatment in the winter at fuel stations? I have heard that places that have can have an affect on your mileage as well.

 

[brian2sun]

Have you been in 4x4 a lot? I get ~9-10 mpgs when I drive in 4x4 for a week.

 

[Duane]

Thanks for the cues guys.

The air filter needs a cleaning indeed, have yet to check the spark plugs.

And yes, I live in Montreal, and the MPG dropped around the same time it started snowing and getting cold outside... Power and rpms still the same though, and the tail pipe is clean. I'll check the O2 sensor as well.

Thanks!

Yup winter operation.... more high idle for warmup, runs richer when cold, you are likely using 4X4 mode more as well. Do you have a remote starter as well and let it warm up for 10 minutes before driving too? 11 seems a little harsh but I know I get quite a few less km's out of a tank when it's cold out.

 

[jacklany]

Thanks for the help people.

I cleaned the air filter, and am back to an average of 16mpg. Winter I guess. I'll see next spring if it goes back up to 18-19mpg.