Really poor mileage.

I have a 02 3.4l V6 Alero andI am getting sometimes less than 250 km/155 miles to a tank. I believe the Alero has a 55 litre/14.6 gal tank. This makes the mileage 10mpg. That's HALF of what it should be. I have changed the air filter, oil change, tranny flush, checked tire pressure.

What's next?

Welcome to AF.

Usually bad gas mileage is caused by a failing O2 sensor.
Though it could be many other things, depending on the cars mileage.

Could be time for a tune up too, might also change the fuel fitler.
This is usually overlooked
and is required that it be changed every 10-20k miles.

Also you dont figure MPG by the actual tank size.
You take the mileage driven on that tank, divieded by the gallons/liters you put in.
This should be averaged over an extended period of time to get an acurate reading.

So if you put in 10 gal of gas and have driven 155 miles then that is about 15mpg, and that is bad.

Both of my 3.4L cars get different mpg.
The SE gets around 22-24 mpg,
and the GT gets around 18-20mpg. :rolleyes:
Which to me makes no sense because my SE is slightly modified :screwy:

Hope that helps!

Thanks for your welcome, and reply.

I figured on the o2 sensor, but wouldn't the service light come on if it's really bad?..at least bad enough to give off THAT poor mileage.

Gas filter should be changed. Should have done that with the tune up...do that tomorrow!

Could improper tension on the serpentine belt cause poor mileage? There is a slight squeak, and the belt shows NO sign of wear.

How about a cold air intake? Would I gain more mileage? And those gimmiky 'Cyclone' intake things. You know...aluminum cylinder that is suppsed to enrich the air. Anyone see results with one of those?

Either way mileage is calculated...155 KM on a tank...not good at all!

A bad O2 wont always throw a DTC.
You can test it manually with a multimeter to check how it is functioning.
Thiers a procedure in the Tips & Maintenance sub forum (http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=2148).

The belt tension isnt a factor realy, but the squeak is normal for these models of GA's. Switching to the goodyear gator back will stop the sqeaks.

A CAI will improve performace and mpg,
but when you are really enjoying that CAI your gas will suffer due to "lead foot'n" .
The cyclone and tornado are crap!! Totall rip off!

I have a similar problem. I tried all kinds of tings nothing helped. I just installed new gas cap I could feel it tightens better than the old one. I did not hear thet pressure releasse sound when I open my gas tank cap for a long time so I tought that my gas was vaporizing much faster. I will let you know if it work.

what size tires you have, did you do any brake job lately on your car, if yes iproperly ajdusted parking brake or dragging brakes can cause poor MPG. Vacuum leaks also. See if you have any leaks in EVAP system, if that valve stays open your engine will suck air constantly and act as big vacuum leak.

No, I checked all the brakes, I did just change them.

Gas cap could be it. I didn't have any pressure release either.

I just bought a 99 Cougar so I will put the Alero on ice for a while...with a little careful driving I have brought the mileage up a bit.

Damn lead foot!

Thanks for your welcome, and reply.

I figured on the o2 sensor, but wouldn't the service light come on if it's really bad?..at least bad enough to give off THAT poor mileage.

Gas filter should be changed. Should have done that with the tune up...do that tomorrow!

Could improper tension on the serpentine belt cause poor mileage? There is a slight squeak, and the belt shows NO sign of wear.

How about a cold air intake? Would I gain more mileage? And those gimmiky 'Cyclone' intake things. You know...aluminum cylinder that is suppsed to enrich the air. Anyone see results with one of those?

Either way mileage is calculated...155 KM on a tank...not good at all!
I didn't quite understand if you said that you did a complete tune-up with spark plugs wires, pcv valves, air filters and all that. Do you still have the factory size tires on. You might also need to change your level octane o gas