Help! My truck's fuel economy is getting worse and worse. I'm down to 6mpg!

Dear Car Talk

Dear Car Talk | Jun 01, 1997

Dear Tom and Ray:

I have a 1992 Ford F150 with a V8 engine. I get really bad mileage. How
bad is bad? On a good day I get six mpg in town. I don't take it on the
highway much, so I can't give you an accurate figure on that. I don't
"hot rod" it, and I take good care of the beast.
The dealership couldn't find any problems with it. They checked the
oxygen sensor and all of the various computers. They said, "Tough luck;
live with it." I have a buddy who told me to try high-performance spark
plugs and an air filter. He said I would definitely see the difference.
What do you think? -- Mike

TOM: The biggest difference you'll see is in your bank balance, Mike. So
save your money.

RAY: This may be one of those situations in which the mechanic at the
dealership is using a high-tech approach and overlooking the simple
stuff. His scanner may tell him that your sensors and computer are
operating properly, but it won't tell him if you have something as
simple as a stuck thermostat.

TOM: A thermostat that's stuck open could make a huge dent in your
mileage. When the thermostat is stuck in the open position, the engine
is, in effect, being "over cooled" all the time. That means it never
gets up to proper operating temperature. And if it's running too cool,
the gasoline won't combust properly, and your mileage will stink (as
will your tailpipe).

RAY: That's why everyone's mileage is worse in the winter. And an engine
temperature problem affects a fuel-injected vehicle (like yours) much
more than it affects an older, carbureted car.

TOM: You need a old geezer to take a look at this for you, Mike; a guy
who was around before engines were dominated by computers. Look for a
guy with white stubble and no teeth, if possible. When you come across a
guy who whistles through his gums and says "Yessshh, Shhonny, shhhtep
right in," he's your man!

* * *

TOM: Hey, do you think you're taking good care of your car? Are you

RAY: If you're like many of our customers, you may be RUINING YOUR CAR
WITHOUT EVEN KNOWING IT. Yes, even you! Find out how. Send for your copy
of our informative pamphlet, "Ten Ways You May Be Ruining Your Car
Without Even Knowing It!"

TOM: Send $3 and a stamped (55 cents), self-addressed, No.10 envelope to
Ruin No.1, PO Box 6420, Riverton, NJ 08077-6420.

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