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Decreased fuel efficiency on 97 Avalon

I have a 97 Toyota Avalon XL with 172k miles. In the past, I have reliably gotten 360-380 miles per tank. This is from normal everyday driving which includes a mix of highway and city miles. A fill-up is generally 15-15.5 gallons (while the owner’s manual says tank capacity is 18 gal, I have never gotten that on fill-up), so average mpg was 23-25. In the past 3-6 months, the miles I am getting per tank have dropped to 260-280 (17-18.5 mpg). My driving patterns have not noticeably changed. I have gotten new spark plugs & wires, tires, and air filter in the last 3000 miles. I have also gotten brake and fuel injector service in the same time frame, and I get regular oil changes. A mechanic has thrown it on the computer and received no codes and less than 5% correction on fuel trims. Is there anything else that could be causing this dramatic decrease in fuel efficiency?

It’s not entirely unusual for mpg to decrease as the car ages. Have you checked your tire pressure? Low tires can cause a loss of mpg. A plugged cat is another possibility. Your mechanic can do a cat back pressure test to say for sure. You might ask your mechanic to check & adjust if req’d the valve clearances, and do a compression test, if those items haven’t already been done recently.

It’s called “wearing out”…It happens to ALL cars, some sooner, some later…Have a compression test performed and compare it to the published figures…Chances are, you will find yours to be at the lower end of the normal range…As rings and valves slowly wear out, fuel mileage slowly slips away…The old girl is 16 years old, her best years are behind her…

I have a 2005 V6 Camry. Same 1MZ-FE engine as yours. 5-speed auto trans. I get about 21mpg combined. I have 66K miles. You have more miles and you may have a 4-speed auto trans, but I’m not sure.

Might be normal for the age of the car.

Is all your maintenance stuff up to date?
A stuck open thermostat will definitely affect fuel economy.
A bad MAP sensor could affect fuel economy

21 MPG out of a Camry? I average 22 out of a V8 Crown Vic! I can put your Camry in my trunk!

(Just kidding, but not about the mileage)…On the open road, where it normally lives, it gets 26-27…

@Caddyman

As you can see, the 4 cylinder Camry gets much better mileage.

There is absolutely nothing wrong with my car. It gets the fuel economy it’s supposed to, as per EPA. I love the car. I’m not complaining about anything.

It is an “open secret” that many domestic cars and trucks get better fuel economy than their Japanese counterparts.

By the way, my Camry isn’t that lightweight and small. It’s smaller than your Crown Vic, obviously.
But it’s actually pretty roomy inside. I have a ridiculous amount of headroom. Even backseat passengers are fairly happy with their accommodations.

My Camry weights 3340 pounds, according to this.

A 2005 crown vic weighs some 600 pounds more. Keep in mind, the crown vic is body on frame.
If it were unibody, the weight difference would be much less.

New thermostats are cheap. I would get one from Toyota.

“It’s called ‘wearing out’ … The old girl is 16 years old”

After 20 years and 217k miles my 88 Accord got the same mileage as when young.
Just regular maintenance including a thermostat every 4 years (every other coolant change).

you had a “brake service”? i would take it back and ask them to chack for a dragging brake. not that it must be their fault, but a car this age it could happen

Thanks for the feedback. I will look into the items suggested above. I expected the car to wear out, I just thought the decline would be gradual rather than all of a sudden. And I should be glad that this is really the only issue (knock on wood) with the old girl.

Thanks again