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Low gas mileage

I have a 2005 4 cylinder Accord. Use to get 35 mpg on highway or better, averaged 30 with everyday driving. Car has 73,000 miles. At 63,000 miles I changed from the Michelin tires that came on the car to Bridgestone Turanze, from V rating to H rating. My mileage has fallen to 24 mpg with everyday driving and just under 31 with hway driving. Have had tune-up, air cleaner changes, car looked at, running fine. Had rear brakes changed at 58,000 miles. My wife says I am now obsessing over this, and am considering getting rid of car. Have tried different gas stations, no significant difference.Any ideas? Can tires matter this much?

My 4-cylinder Accord (5-speed) has Turanza Serenity tires (H speed rating) and still gets 32-34 mpg on the highway and 27-28 locally.

This is less than it used to get, but I don’t think it’s the tires.

The biggest difference I can tell is that most gasoline in my area is now 10% ethanol. Both of my cars lost 3-4 mpg since the introduction of E10, and have levelled off there.

That was before the Turanzas were installed. I noticed no significant change with the new tires, which were installed about a year ago, at about 95k miles.

Are you sure the tires are correctly inflated? Tires can make a difference in fuel mileage, but tire pressures are also important. I run 35 psi all around in my tires, which is slightly above the pressure recommended on the door-frame sticker. It seems to work well for me.

Even if the tires are at fault, why sell the car? New tires cost a lot less than a new car. Personally, I’m so happy with the reduction in interior noise I’d be willing to accept a slight reduction in fuel mileage. All tires are different.

Tires have different rolling resistance and therefore do give different mpg on the same car. If you went from a tire with low rolling resistance to a high resistance tire the difference could be as significant as you describe.

In most cases switching tires makes a little difference and since most folks don’t compute mpg every tankful they wouldn’t notice. You noticed the difference in your car.

Is the check engine light on? Have you had the car scanned for trouble codes?

Check that your thermostat is working properly. Your car may be running too rich because the car is running as if the engine is cold and using too much gas.

There is also a difference in gas mileage between warm and cold weather. Are you comparing mid-summer to late fall mileage?

If they are properly inflated, it is not the tires. They might be good for a 0.5-1 mpg difference but not 4.

Don’t get rid of the car, that’s just silly. You’re going to get varying gas mileage over time that’s just the way it is. Listen to your wife.

The EPA estimates for the 2005 Accord 4-cylinder are 23 city and 31 highway for the manual and 21 city and 31 highway for the automatic. You are getting exactly the kind of mileage that your car is rated for.

Tires can make a big difference in mileage.

Also, the weather is getting cooler. That alone can drop mileage significantly because your engine is running richer longer.

I agree with your wife. As long as the car is running well, is well maintained (which it sounds like it is), there are no warning lights, and the tires are properly inflated, I think you should just appreciate the car and obsess about a real problem.

Thanks for your response. I actually put on Potenza tires; my wife had Turenza tires. The tires are properly inflated.I tried using gas that does not say 10% ethanoland this sometimes makes a difference.

I am getting obsessive, checking mileage with every tankful. I think it may be a combination of the current tires are not LRR and there is more ethanol in the gas.

My wife agrees with you.

Mine was rated at 24/34, the 2006 was rated 21/31, when they changed the calculation method. I was actually doing better ten the rating until I changed tires.

Thank you. Have noticed no difference in mileage with weather-have gone thoguh one winter and one summer with these tires…

No check engine light, nothing on the computer. Dealer says if anything was wrong the engine light would come on.Tires inflated properly. No change in mileage with weather. Thanks for your response.

Something that is often overlooked is the O2 sensor. An old sensor can reduce milesage and should be changed. If it does not change your mileage then no harm no foul since they should be replaced when mileage dictates.

When you converse with the dealer you’re generally talking to a service writer. Very very few of these people have what one would consider even a mild amount of mechanical ability. Their job is to shuffle paper, poke keyboards, and generally lay down enough BS in the hopes they will appear to be knowledgeable about cars.

They are wrong by stating the CEL will be illuminated if any computer codes are present. The light does not have to be on at all. Get AutoZone, Checkers, etc. to scan the car for you. It only takes a few minutes and they will do this for you free.

If no codes are present you might consider the possibility of an iffy thermostat which could be aged and opening at a lower engine temperature.
I certainly would not consider getting rid of the car over this issue.

The pre 2008 ratings were quite…optimistic. The revised estimates are much more realistic. The numbers I quoted are the revised estimates for the 2005 Accord. The fuel economy you are getting is nearly identical to what the car is supposed to be getting. I doubt if there is anything wrong with your car.

I had a minivan with a Mitsubishi v-6 and at 70,000 miles the mileage started dropping until 85,000 miles when my mileage was only 60% of what it was, at that point my check engine light came on and indicated an oxygen sensor problem. When I replaced the sensor my mileage went right back up.
I guess the point I am trying to make is that an oxygen sensor can hurt your gas mileage long before it sets the check engine light.

One thought that came to me as I was reading the more learned responses is, “Is the change in MPG real?” That is, the tires themselves seem unlikely to make a real change in the MPG, but if the circumference of the new tires is larger than the circumference of the old tires, then the car would APPEAR to be going fewer miles on the same tank of gas. The “miles” in the MPG calculation is coming from the odometer, which is inversely related to the circumference of the tires.

So the question - are the new tires exactly the same size as the old tires? If not, the difference in MPG may just be imaginary.

Good luck.


Check your coolant temp sensor and thermostat operation in addition perhaps to O2 sensors.

Do not believe anyone who says “the computer would know” - eventually the computer will catch on if it is something like this. But the computers tend to tolerate a lot more deviance than I do.

Thanks. Same size tires. Only difference is speed rating.