Mileage Drop

[Hank F.]

My 93 ATX was doing 30+ mpg highway last summer whether I was driving 80 or 50. My overall was consistently 22-25. Now, I am lucky to get 17, with no change other than winter. I have changed to buying name brand gas, usually 76 or Exxon, and no more mixing mid grade with high-test. I do have one unusual symptom. When starting, with no throttle, the car revs to 2000 on its own before settling to idle. I know that this is like the Dr. telling you to hold your kid up to the phone, but I am hoping maybe someone recognizes this illness of my car. Thank in advance for any advice.

 

[shoteen95]

Often with the colder temps, comes a noticable reduction in gas mileage, especially with ATX SHO's. A big factor in this is that it takes a lot longer for the transmission fluid to warm up to the point that the torque converter(TC) will lock. TC lockage = reduced RPM's, better mileage, lower trans temps.

Here in MI, when it's cold in the morning and my car's been sitting all night, my torque converter will not lock up no matter how long I drive it unless I let it warm up, and shut off/restart the car. Then like magic, my TC locks up like it should.

Have you noticed the torque converter not locking up lately? Pulling more revs than you're used to while cruising probably means your TC is not locked. I've also noticed that the RPM's will fluctuate more with slight throttle inputs when the TC is not locked compared to when it is while i'm cruising on the freeway.

Also, how has the maintainence on the car been? Have you checked for any codes lately? Check engine light? Worn O2 sensors can also ruin your mileage. My car will sometimes rev pretty high (close to 2k) when first started, but I'm not worried about it much.

 

[spazmoid]

Hey my car was getting 25-26 mpg running 80 miles straight on the highway with a little around driving mixed in, with a minor hole in the exhaust, and now with the exhaust fixed i'm getting 21-22mpg in the same driving. It doesn't make much sense, but all i can say is that it did get a bit colder, and if i saw a drop like that even with fixing the exhaust then the weather alone must effect it alot.

 

[Hank F.]

I talked to my 90 years young Father, and he said that winter driving has always resulted in less mileage for a lot of reasons that I sure didn't take into account; like slippage from icy roads, cold engine metal takes longer to heat up to operating temp., and therefore your overall tolerances are much looser, more friction from cold grease in wheel bearings, my ATX taking longer to get to op temp. etc. etc. These things taken individually don't seem like much, but collectively they probably do add up to my 4-5mpg. loss. What's that old saying about the older I get, the smarter my Dad seems to me. He was born before America entered the FIRST World War.

 

[SHOck]

LOL... these ain't your father's old tar grease bearings! Cars warm up much quicker now than they did forty years ago, too. ****, my 84 Stang took twice as long as the SHO.

Gas is the biggest culprit these days, but make sure your ATX is getting warm enough to lock up. There's been a few that ran for years with a no-lock problem, or extended warm-up periods. That alone will yank 3-5mpg.

As far as the high idle is concerned, might be a vacuum leak or slow MAF. I'd start by cleaning the MAF sensor. If the high idle persists, spray some carb cleaner around the vacuum lines while it is idling high. If idle increases, you've got a vacuum leak issue.

Propane gas is better to use for this if you've got a torch.

 

[93rev2sev]

A slight drop in economy can be as simple as a bad alternator.

I actually noticed a drop in economy when daylight standard time came.

Running with lights on all the time made the difference.

 

[TankII]

Did they switch to 10% ethanol based gas in your area? If so, that's probably it.

TankII

 

[Hank F.]

Tank, I think you must be a mind reader because as of Nov.1, they alcoholed all the gas! I am completely out of warranty and brains. You guys all thought of stuff that didn't occur to me. Thanks- several heads are truly better than one.