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Declining gas mileage

I have a manual 2000 Ford Focus ZX3. It has about 140k on it. When I first purchased it (new), it would get about 33 mpg on the highway. Now, I’m lucky to get about 28. Any suggestions on why this would happen and/or what I can do to improve this?

First, you need to tell us about the state of maintenance of this car.
Is all of the maintenance up to date, as per the Owner’s Manual?

Have you checked your tire pressure recently?
Do you live in a region that is experiencing cold winter temperatures?
Is ethanol added to the gas in your area of the country during the winter?

All of those factors play a role in fuel economy.

The issue is independent of weather. Oil is regularly changed. Tire pressure hasn’t changed. Plugs and cables were replaced a few years ago. Serpentine belt was replaced in the last year. Other than that, no other repair or maintenance has been done. I have had very little work done on this car (knock on wood). It has been excellent.

A lot of the states in the Northeast US have gone to E10 (10%) ethanol gas blend year round. NJ has been E10 only for the last couple of years, it’s dropped my mileage roughly 7 to 10% on my Blazer (~17.5 was 19) and Caprice (23 to 21 mpg) in local driving (semi-rural).

Ed B.

Hmmm… I’ll have to check that. I’m in Ohio. Thx.

You need to get your owner’s manual out. There are other things that should be done on that car and you are behind right now. Things like changing the brake fluid (Safety issue) You are past due for a transmission fluid change and filter cleaning (Auto or manual transmission?) A few cars are not recommending regular transmission fluid changes, but almost everyone here is going to suggest it is foolish not the change it out at about 30,000 - 80,000 miles.

How are you measuring the mileage?

Are you driving faster. Also your tires can attribute to small difference especially if pressure is not maintained. Last the aforementioned ethanol in fuel takes it toll too.

Did you actually measure 33mpg or was that the winder sticker? remember they derated these a few MPG to reflect the real world not the EPA fantasy driving world.

Is your oil suitable for cold temperatures. 10w30 recommeded for all year, but 5w30 may do better in cold, easy starting too. Your oxigen sensor may be worn, thus incorrect fuel/air ratio. Have you swithed to other gasoline brand? Driving fast will affect mileage big time too. For instance I had Honda Accord year back and I did alot hightway driving. If I would drive it at 120 km/h I would get 500 km on tank, but If I drove it at 95 km/h using cruise control I was getting 750 km on tank.