huge MPG change

[Douglas Ferdarko]

I have an 01 ST 4x4 5spd with 100k on it. I have been getting 18-19mpg summer/winter for the past 2 plus years. I did a tune-up this summer with no changes.

I went from 255 to 265 tires and I added an aussie locker in the past 2 weeks. Today I filled up and this tank was 13mpg. My driving habits if anything have gotten better. I commute 30 miles round trip daily to work and have dropped my speed from 65mph to 60mph during my commute.



What would be the cause for the 5-6mpg loss?



Thanks

Doug

 

[Travis Munday]

One tank of gas is nothing to get concerned over, wait for at least two more fill-ups to see if the trend is consistent. Coulda been some bad gas, strong winds, increased weight, any number of things that could lead to an errant result. Just give it a little time.



BTW, mph isn't really the important thing when it comes to MPG, RPMs are, particularly in a 5-speed. You could be doing 60 mph in 3rd gear at 4500 RPM and get much worse MPG then going 60 mph in 5th gear at 1500 RPM. Watch those revs rather then speed.

 

[blksn8k]

Just curious but have you done anything to correct the speedometer after the tire change? Larger tires will cause the speedometer to read slower and the odometer to show fewer miles driven since the tires rotate fewer times per mile due to their larger circumference. If you are basing your calculations on your odometer reading it will appear as though you are traveling fewer miles per gallon.

 

[Jimmy Lavoie]

Agree with blksn8k.

 

[Todd Z]

In the FAQ is the tire calculator....



IT says your speedo is now 1.8 % too slow.....



That is not 18 to 13 but if you have to give it more throttle to get going...



Did you change the second number of the tires ???



ALSO are you sure you filled the tank to thew exact same spot ???



Todd Z

 

[Richard L]

As previously stated, one tank of gas is not very accurate for judging your overall fuel mileage.



Your oversized tires are probably enough to throw off your Speedometer and odometer. The larger tires will make you go faster and farther than is indicated so you are not seeing your true miles traveled.



Also, if you have not checked your tire pressures, the tire shop may have lowered the inflation pressure and that causes more roll-resistance to the tires and uses mor fuel. Most experts recommend at least 4-5 PSI above the standard inflation pressures. Most people here probably run 35 PSI in their Sport Trac tires..



There is probably a very small drop in your actual gas mileage, but it is being exaggerated by the speedometer/odometer error.



You might be able to get your dealer to recalibrate the speedo for the new tires. It should only cost you about $50 or less



...Rich

 

[Doctor CAD]

Ethanol causes much lower MPG's



Get used to it!

 

[Greg Stuhlsatz]

I don't think you can run ethanol in a 01.

 

[Gavin Allan]

We have no choice around here. All gasoline contains ethanol. I know, it sucks, but the corn processors are getting rich.

 

[Dreman]

Most fuel has 10% or so ethanol in it nowadays. 10% is not enough to throw off the calibrations, so you can run it in cars and trucks that aren't flex fuel. But 10% ethanol is also not enough to change the mileage by more than maybe 5%.

 

[Ray McIntireJr]

You can run the 10% ethanol because I read it in my owners handbook.

 

[Woppy V]

what kind of tires are they and are they fully inflated?



I put 265 bridgestone revos without fix the computer and went from 400 a tank to 350 a tank.

 

[Gavin Allan]

Big Corn has us by the shorthairs.