I have an 07 Mazda 6 and for a while now its been getting really bad MPG. Ive calculated sometimes as low as 9 MPG highway. Just a few days ago I used a whole quarter tank going about 50 miles. But the thing is that its random. Sometimes ill get great mileage. Ill drive 100 miles and the needle will barley move. Still 90% of the time its bad though. What could be going on its driving me nuts. The car has about 64 k on it now and I've taken great care of it.

 

What engine? Is there a loss of power?

One small stupid thing- if you have access to a floor jack, jack it up and make sure you don't have a brake dragging. You should see uneven pad wear, or even hear noise, but you never know.

Another way that may tell you there is a dragging brake is feeling the temp of each wheel after you've been driving. If one is dragging, simply touching the outside face of the wheel will tell you.

Do you use the parking brake on a regular basis? Perhaps the linkage is sticking at times, but not at others.


Anything engine-wise that would cause such a drop should be fairly evident. Off-hand the only thing I can think of is the dreaded cat melt-down on V6 cars. You'd know if this was going-on by simply opening the hood after driving. If they're breaking-down to the point of 'choking' the engine, you'll feel the heat.

Do the stupid thing and make sure the air filter isn't plugged. It's the time of year for critters to look for stupid places to build a home. Spark plugs shouldn't cause such a swing. And again, anything engine-wise should cause a drop in power. I really wonder about the brakes.

 

Its the 4cyl. Never use the parking break and really no loss of power either

 

Do you fill the entire tank before calculating mileage? If you are making piecemeal calculations, it may be the fuel gauge that is providing the problems. I can easily hit 500 miles on a tank of gas in my 05 4 cyl (w/MT). But the first "half" per the gauge will show over 320 miles and the last half only about 180.

Also, I agree with the post on checking brakes. You should use your parking brake regularly. If you don't, you can run into a situation where you need to use it once on a steep hill and then the parking brake will freeze in place. This is possible for all cars of all makes.

 

Ever put fuel system cleaner in it? 64 K mileage --- spark plugs is a good idea.

 

Fuel system cleaner is worthless; contemporary gasoline has all of the additives and "cleaners" necessary to keep fuel systems perfectly clean for the life of the car. As for replacing spark plugs after only 64,000 miles, you already know what I think about that idea; a waste of money.