Bad Gas Mileage And Thumping-ish Sounds

[Daytona]

^Funny. I just read your thread before seeing you post here about it.

It's very similar to your issue, however I hear it more when the car is colder than warmer and I can't hear it as well at higher speeds. It's a rotating sound which is why I can hear it better at slower speeds. I, too, thought about maybe one of the wheels' lugs being loose but haven't had a chance to check that out yet. Will have to experiment with braking and see if it does anything to the sound like with yours. Will let you know.

How many miles do you have on it?

I have been wondering latley on mine 01 with 48k, gas mileage bounces around 25-28 mpg mixed hwy and city. What I have been wondering is maybe the 100k plugs aren't doing well with age. It baffles me that Neons (yes my other car used to a be Neon and I still work on them) burn through plugs about 15k-20k how can an Alero or for that matter any other car not burn up plugs in under a 100k.

In mine when the fuel mpg dipped below 25 mpg I cleaned the air filter(K&N) and cut holes in the airbox to allow more air to enter. Yes it is from the engine bay, but with the airflow you get in the engine bay at highway speeds how warm can this air be. ( I could get into a whole 'nother conversation about that) I also replaced the fuel filter and ran Seafoam through it. Gas mileage jumped back up and has been good ever since. This was about 20k ago.

So in short. When was the last time you check your plugs, fuel filter and air cleaner? Air pressure in your tires could also cause a problem and with the cooler air you might check and see if you are underflated.

As far as the clunking or knocking sound can you hear it more with the window down? Have you tried driving Ace Ventura style or in the passenger side and see if you can narrow that down? You may get strange looks, but if you can keep from paying someone to fix it, it maybe worth the embarassment.

Just my opinions.

[Daytona]

Car's got 41K miles on it. I bring it in for every recommended servicing per the owner's manual. My plug wires had to be replaced a few months ago, otherwise no unusual wear internally. Front tires are only 6-8 months old and are holding their air fine.

Noise is more noticeable with the windows closed though haven't tried driving with my head out the window.

[BlackJack]

check the rotors / drums for warpage, and check the wheel bearings. Jack the car up, put it in neutral (key off) and manually rotate the wheels one by one. If you hear a "dragging" or light grinding noise only at certain locations throughout rotating the wheel, then there's your likely culprit. Either one will make your gas mileage go down, and cause a grinding or thumping noise when driving.

Even if your tires are balanced correctly, it will still feel like something is out-of-round.

Also, check the amount of "play" in the wheels by grabbing the tires at positions 9 o'clock and 3 o'clock and jiggle the wheel. If you have an unreasonable amount of movement (light clunking), then higher likelyhood to the wheel bearings being bad or center nut needing to be retightened (check required torque values).

Thirdly, check to make sure all your inner CV's are tight.

[Daytona]

^Thanks for the advice. The dealership culdn't find anything "wrong" with the car that would explain the noise or the drop in mileage but did tell me that my brakes are now borderline and need to be replaced at or before my next oil change. That'll be my 3rd set of front brakes on a car with barely over 41K miles and I don't race the car! Plus they said that my rotors need to be recut and if they can't do that satisfactorally they'll need to be replaced. If my rotors are a little warped, that'll explain the uneven braking sound and maybe the rolling noise. Replacing them would solve that - no? All total I am now looking at over $400 in repairs. Merry F---ing Christmas to me. issed:

[brsexton]

Originally posted by Daytona@Dec 31 2005, 09:04 AM
^Thanks for the advice. The dealership culdn't find anything "wrong" with the car that would explain the noise or the drop in mileage but did tell me that my brakes are now borderline and need to be replaced at or before my next oil change. That'll be my 3rd set of front brakes on a car with barely over 41K miles and I don't race the car! Plus they said that my rotors need to be recut and if they can't do that satisfactorally they'll need to be replaced. If my rotors are a little warped, that'll explain the uneven braking sound and maybe the rolling noise. Replacing them would solve that - no? All total I am now looking at over $400 in repairs. Merry F---ing Christmas to me. issed:

Quoted post

If I were you I would not pay the dealer that kind of money to use the same subpar GM parts. GM brakes suck and wear fast. I have 46k miles on my 03 and have been through 2 sets of OEM brakes and rotors. The last time, I bought Napa rotors and Akebono pads. I have had them for well over a year and several thousand miles and no sign of wear.

[Daytona]

^Something to keep in mind for next time.