Decreasing MPH @ 39K???? - Nissan Xterra Forum
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#1 Old 01-27-2013, 03:23 PM
Farleyjc
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Decreasing MPG @ 39K????

Hello,

I have a 2005 X-Terra and have been noticing decreasing mpg in the recent months. I normally got close to 18 mpg and now am getting about 16 mph. Driving habits are the same.

I admit that the truck has been gas and go with minimum maintenance (change oil, wipers, belts...) and my first thought was the spark plugs may be due to be replaced. However, looking at the maintenance schedule, they do not get replaced until after 100K.

Any ideas on why the mpg has fallen?

PS. Thanks again to all the forum who recommended E-Trailer and gave me advice on installing a trailer hitch and wiring harness. BTW, E-Trailer matched a lower price AND gave me free shipping for the harness in accordance with their "price match pledge".

Last edited by Farleyjc; 01-27-2013 at 06:40 PM. Reason: correction
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#2 Old 01-27-2013, 04:14 PM
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Are you asking about decreasing MPH (miles per hour) or decreasing MPG (miles per gallon)? I think the latter.

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#3 Old 01-27-2013, 04:21 PM
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Originally Posted by RacerXXL View Post
Are you asking about decreasing MPH (miles per hour) or decreasing MPG (miles per gallon)? I think the latter.
Correct. Thx.
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#4 Old 01-27-2013, 05:50 PM
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It sounds like Winter Gas to me. I can't see your location because I am on my iPhone right now, but I would bet that is it. Check your tire pressures as well. 16mpg still isn't bad at all. That's pretty good for the size of the truck.


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#5 Old 01-27-2013, 06:45 PM
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Originally Posted by ryandavenport View Post
It sounds like Winter Gas to me. I can't see your location because I am on my iPhone right now, but I would bet that is it. Check your tire pressures as well. 16mpg still isn't bad at all. That's pretty good for the size of the truck.


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Yes, I suppose winter could have something to do with it. I am in Prescott, AZ. which is North Central AZ and we are at 5,000 feet. It gets cold and snows on occasion. I have had to add air to my tires 2x so far this winter...about 4 pounds each time. Four pounds seems to be when the sensor alarm goes off.

Question: Is there much difference in air pressure early in the morning as opposed to late afternoon? In the winter there is about a 25-30 degree temp. difference.
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#6 Old 01-27-2013, 09:58 PM
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There shouldn't be a big enough difference to matter on that. Just be sure to fill the tires to the proper pressure when they are cold. It's impossible to keep them perfect unless you have a full time pit crew. Also, not sure if you know this but a large difference in pressures can also throw the light, even if the highest pressure and lowest pressure are both within the acceptable parameters.

Go ahead and average your mileage until spring. When summer gas comes back out (March or April) and you are still getting the same mileage, it may prove you have an issue, either in your foot or the truck.


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#7 Old 01-27-2013, 10:15 PM
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There can be. Assuming the morning temperature is freezing (32*F), and you have 35psi in a 32x8 tire with a 16" rim, after a 30 degree rise, you'll end the day with a tire filled to 37psi. This is only ambient temps here, so if the vehicle is driven, then there will be additional pressure changes.
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#8 Old 01-28-2013, 12:18 PM
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On my 05 I definitely saw a hit in my fuel economy with the winter gas here in Tucson. Though there are a lot of factors that can contribute to low fuel economy. I'd say 16 is right where it should be for this time of year though if it's mostly stock. I get worse because of beefier tires and a lead lined foot

Have you tracked gas usage from years past?
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#9 Old 01-28-2013, 12:42 PM
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Have you changed your air filter regularly? I don't know how big a factor it truly is, but all the regular maintenance can't hurt. Dirty filters impede flow. Changing the oils, all of them, can help too, sludgy oil takes more effort to slarsh around.

Up until I put on my Duratrac's I was flirting with the 20mpg line at times, averaging 18.55 overall. Of course my X is newer so going to have less diminishing returns overall, and I don't know how much extra weight your packing in mods, if any.

A good old tune up and general maintenance might bump you back up where you are used to, and that is just good stuff to do anyway so you won't be doing any harm trying.

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#10 Old 01-29-2013, 07:13 PM
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Originally Posted by Revu View Post
On my 05 I definitely saw a hit in my fuel economy with the winter gas here in Tucson. Though there are a lot of factors that can contribute to low fuel economy. I'd say 16 is right where it should be for this time of year though if it's mostly stock. I get worse because of beefier tires and a lead lined foot

Have you tracked gas usage from years past?

I don't need to track it. I have a 2005 SE and the odometer has a gadget with several settings and one of them tells me the current mpg as you are driving. This is my 3rd winter in Prescott, AZ. and the lowest the MPG has ever been.

As far as maintenance goes, I follow the schedule at a minimum and replace the air filter more than needed.
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