Gradually declining MPG

[bill602]

I bought a used '05 Prius with 10 k miles on it in Dec. 05. The MPG quickly ramped down to about 45. I've been noticing that it has been gradually dropping ever since. When I say gradually, I mean that from July, 06 to now (May, 07), the mileage has steadily dropped from about 44.9 to 44.2. I have been keeping up with the scheduled maintenance and changed the air filter last Nov. or so. That caused the MPG to go up about 0.01 mile/gallon. I nearly always fill up at the same gas station. My driving habits, trip length, terrain, miles per week, etc. have all remained the same, but the MPG trend is always downward. Is there anything I can do to bring it back up?

Thanks,
Bill602

[tripp]

<div class='quotetop'>QUOTE(bill602 @ May 10 2007, 08:48 PM) [snapback]439652[/snapback]</div>

I bought a used '05 Prius with 10 k miles on it in Dec. 05. The MPG quickly ramped down to about 45. I've been noticing that it has been gradually dropping ever since. When I say gradually, I mean that from July, 06 to now (May, 07), the mileage has steadily dropped from about 44.9 to 44.2. I have been keeping up with the scheduled maintenance and changed the air filter last Nov. or so. That caused the MPG to go up about 0.01 mile/gallon. I nearly always fill up at the same gas station. My driving habits, trip length, terrain, miles per week, etc. have all remained the same, but the MPG trend is always downward. Is there anything I can do to bring it back up?

Thanks,
Bill602
[/b]

Have you checked your tyre pressure?

[Marlin]

How about tire wear? A 1/8 inch decrease in your tire tread would result in about a 1% decrease in the distance traveled for every wheel revolution. So the miles driven would be under reported by 1%. The difference in mileage you are reporting (44.9 to 44.2) is a 1.5% change.

[mpgFanatic]

<div class='quotetop'>QUOTE(bill602 @ May 10 2007, 10:48 PM) [snapback]439652[/snapback]</div>

Is there anything I can do to bring it back up?
[/b]

No.

It is all part of the aging process. From the age of 16, when you knew all the answers and were at your physical and sexual peak, it all goes downhill. So the decline you are seeing is all very normal.

Just be grateful you can still keep-it-up in the 40s.

[morpheusx]

I agree that it is most likely the tires. I find that 40 psi front 38 psi rear give good handling and ride comfort and increases the mileage a little, 4 of my tanks have been 90 % highway and I have easily recorded in the 49 - 51 MPG range on all of them even with driving most of that at 72 MPH.

Another tip I would try is putting in a good fuel injector cleaner at your next tank ( I recommend Lucas Oils - Fuel treatment ) It costs about $5 for the one treatment bottle and about $12 for the bigger bottle and I would almost guarantee the following tank will net a significant increase, I always add the same time I change oil on all my cars its easier to remember that way. Heres a link to what I'm talking about, I always buy it at Advance Auto parts, but I believe it is available nationally at Autozone and other similar stores.

http://www.lucasoil.com/products/display_p...=2&loc=show

[Tom_06]

<div class='quotetop'>QUOTE(Marlin @ May 11 2007, 08:18 AM) [snapback]439793[/snapback]</div>

How about tire wear? A 1/8 inch decrease in your tire tread would result in about a 1% decrease in the distance traveled for every wheel revolution. So the miles driven would be under reported by 1%. The difference in mileage you are reporting (44.9 to 44.2) is a 1.5% change.
[/b]

That makes the mileage seem better as seen in the MFD since that is based off of wheel rotation.

- Tom

[richard schumacher]

Check tire pressure whenever the average outdoor temp changes much more than 10 degrees F, or at least monthly. If you have not been doing that, buy a $5 digital tire gauge, use it for a couple months and see what happens. (Remember that pressures should be checked when tires have *not* been driven more than a few miles in the preceeding hour. First thing in the AM is the perfect time.) Betcha a nickel that it solves your problem.

Don't bother pouring any snake oil into the tank unless you're in the habit of buying Brand X gas (yeah, I know, all gasoline is the same; the stuff added when it acquires a brand name makes the difference, and those additives do the same job that snake oil does).

[Marlin]

<div class='quotetop'>QUOTE(Tom_06 @ May 11 2007, 09:10 AM) [snapback]439838[/snapback]</div>

That makes the mileage seem better as seen in the MFD since that is based off of wheel rotation.

- Tom
[/b]

Oops, you're right.

[morpheusx]

<div class='quotetop'>QUOTE(richard schumacher @ May 11 2007, 09:44 AM) [snapback]439861[/snapback]</div>

Check tire pressure whenever the average outdoor temp changes much more than 10 degrees F, or at least monthly. If you have not been doing that, buy a $5 digital tire gauge, use it for a couple months and see what happens. (Remember that pressures should be checked when tires have *not* been driven more than a few miles in the preceeding hour. First thing in the AM is the perfect time.) Betcha a nickel that it solves your problem.

Don't bother pouring any snake oil into the tank unless you're in the habit of buying Brand X gas (yeah, I know, all gasoline is the same; the stuff added when it acquires a brand name makes the difference, and those additives do the same job that snake oil does).
[/b]

say what you want and call it snake oil, but when you can actually see the gain after a few hours of driving you'll change your mind, and I always have bought my fuel at quality high volume stations. The problem here lies in the fact that MOST stations only add their advanced detergents to their premium (usually the 93) the regular (87) has the minimum requirements.

[bill602]

I have been keeping all the tires at 36 psi, but I'll try the different front & rear pressures from Morpheusx. I'd say the additive is worth a try to see what happens. If it delivers the results, it would be worth it.

As far as tire wear goes, there's not much you can do about that. I should say that I put two new tires on the front and then a few months later on the rear during the period that the mileage was dropping steadily, but didn't think to check for upswings in gas consumption after each new pair.

Thanks to all for the input.

Bill602