Dayton Daily News

Wheels: An e-mail from David says, "I am the sole owner of a 1998 Camry (4-cylinder) with 128,000 miles on it. It is in seemingly great condition, as I have maintained it with great care, with regular oil changes (4,000-5,000 miles) and all the other routine maintenance requirements. But since November 2006, (tuneup) and new tires (December 2006, Goodyear Comfort Treads), my fuel economy has decreased

12-15 percent. At first I thought it was the colder winter temperatures, but spring has brought no improvement. I used to get 29 mpg when I drove at 70-75-plus mph (2700-2800 RPM), before the cost of gas skyrocketed. After

nine years' experience with this car and some experimentation, I became convinced that 2400 RPM represents the "sweet spot" for maximum economy in this car, but I can't prove it.

My slower speeds did increase my fuel economy to the point where I was getting 550-570 miles per

18 gallon tank (31-32 mpg), but since November 2006, my mileage has dropped to as low as 465 miles (26 mpg). I just replaced the air filter and got 520 miles out of my latest tank (29 mpg).

Throughout March and most of April, I was never able to get more than 500 miles out of a tank of gas. I don't use any one particular brand of gas. Air pressure is proper, and alignment is good. Engine RPM at various speeds has not changed. There are no oil leaks or smoky exhaust emissions.

I mentioned this to my local Toyota dealership (who does most of my maintenance) and they said that without the check engine light illuminating (it's not), there's nothing they can do. I did notice some mild engine surge at idle a month or two ago, but that stopped and has not recurred. The car looks great, runs great and seemingly has no problems, except the decline in fuel economy.

Any ideas? (PCV valve, some kind of vacuum leak, the new tires??) Or is increasing vehicle age/mileage the primary culprit? Or am I being too "anal" over "normal" fuel economy fluctuations?

Halderman: With your history with the vehicle, it appears that something happened and that could be two things:

1. The tires are very good but may not be low rolling resistance-(LRR) type tires.

2. Try adding a few psi to the tires to see if this helps.

There is nothing you can do about the fuel economy, although with that many miles adding a can of Techron to the gas may help.

The advice from a Goodyear engineer is, "The tires could be some of it. Worn tires give the least rolling resistance so depending on what the old tires were, there could be 2 mpg between old, low rr (like if they were OEM tires) and the new, deep non-skid ComforTreds. I can easily see

1 mpg difference. I looked up this vehicle and it has an 18.5 gallon tank and is EPA rated at 23/30 mpg."

James D. Halderman is an ASE-certified master technician.

E-mail at jhalderman2@juno.com., or write him in care of: Wheels, Marketing Publications Department, Dayton Daily News, 1611 S. Main St., Dayton OH 45409.