Mileage Decreasing - Diesel Forum

IMartin · 08-11-2003, 04:38 PM

I posted once before at 10K miles I was dissapointed with 12.2MPG towing roughly 5000 lbs on highway at 70-75mph. Towing the same load on the same highway same speeds, now with 20K on engine, I'm down to 10.9-11.2 on mileage. Oil and filer change on time, new fuel filter at 15K, and air cleaner is not showing signs of restriction. All motorcraft parts used for maintenance. Any ideas???

RoyC · 08-11-2003, 06:00 PM

Is MPG from overhead computer or hand calculated?

RoyC

pabrannan · 08-11-2003, 10:01 PM

IMartin, I just got back from a 6.5k trip from Fla. to Grand Canyon and averaged 12.00 hand calculated and I was pickled tink. I get about 18 solo at home in Fla. My gross weight towing is 13k and solo is 8k. Oh by the way I drove between 65 and 75 and on average 70mph.

JMHO and experience,

Paul B

swhitney · 08-11-2003, 11:22 PM

With 20k on the air filter it is probably the culprit. Had the same issues, swapped out the air filter at 28k (still no restriction showing on the gauge) and picked up the 1-2mpg that had fallen off.

rxbike · 08-12-2003, 12:00 AM

What kind of mileage are you getting at 70-75mph without the trailer. Gearing on mine allows for optimal mpg @ below 2000 rpm with 3.73. Without a load keeping her at 68mph, I can get 19 mpg average. Towing my 28ft TT I get 12mpg @ 65mph average. You may be pushing the rig too har @ 75mph while towing my guess .

jschira · 08-12-2003, 08:10 AM

That 2000 rpm has something magical about it. Many people report a significant drop off in mileage above 70 mph (about 2000 rpm).

It might be wind resistance of the truck, not the gearing/rpm's.

issanni · 08-12-2003, 10:09 AM

My fuel economy dropped way DOWN just before my CMP went bad, also found out the exhaust back pressure sensor was bad too.

When I say it dropped way down, I mean this: Non-towing I was getting 14-16mpg around town driving and when it went down I was getting 10-12mpg under the exact same conditions.

With a new CMP and exhaust backpressure sensor the fuel milage is back up to around 14-16mpg in town... [img]/ubbthreads/images/graemlins/shrug.gif[/img]

IMartin · 08-12-2003, 12:18 PM

Thanks for the post guys. The mileage is via the computer, but has been hand verified as pretty accurate several times. I don't do any miles at highway speed without a trailer. In fact, I never hit the highway Mon-Fri. It's 11 miles to/from work at 45mph max. I'll change the air filter despite the guage not showing a need to. I have the 3.73 rear end. I have heard that 70mph and 2000RPM is the magical combo. Thanks again.

dmftoy1 · 08-12-2003, 02:52 PM

You've got 20k on that air filter? If you can, take a picture of it. At 8k mine was pretty filthy, and I'm curious as to how yours looks.

Regards,
Dave

JADFPE · 08-12-2003, 03:04 PM

My air filter was dirty enough at 7,500 miles for me to change. I now change the air filter every 7,500 miles no matter what the restriction gauge is showing.

John [img]/ubbthreads/images/graemlins/cool.gif[/img]

orion7144 · 08-18-2003, 03:14 AM

My rear pinion seal is bad and leaks. I noticed a decrease in MPG when the fluid was getting low. Just a thought