7.4 mpg!!! - Dodge Cummins Diesel Forum
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post #1 of 43 (permalink) Old 03-19-2017, 09:02 AM Thread Starter
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7.4 mpg!!!

Can anyone help me understand why my trucks mpg all of a sudden went from 10 to 11.5 mpg to 7.4mpg when my odometer rolled to 20,000 miles. This mileage is while towing my 20,000# RV. When it started this I figured it was just a regen cycle buy now its been doing this for the last 400 miles of highway driving towing so i don't think its a regen causing this now and if it is then its stuck in regen.
Rhonda and i swear it started this the minute the truck's odometer rolled to 20000 miles. We have always gotten 9.7 to 11.5 mpg driving on rolling hills so something must be going on. I know i did just install 6 new tires but i stayed with oem size and the bad mileage was also with my old tires on the truck. I just think something weird is going on, my truck appears to be running fine so im puzzled.
Any thoughts would be appreciated.

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post #2 of 43 (permalink) Old 03-19-2017, 09:06 AM
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Did you go from the Transforce to Super Swampers?? That would kill a couple of mpgs!

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post #3 of 43 (permalink) Old 03-19-2017, 09:09 AM
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You could have picked up the last of someone's the winter blend, besides you are towing heavy with a head wind 7.5 could rapidly happen. Have you analyzed the oil recently?

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post #4 of 43 (permalink) Old 03-19-2017, 09:24 AM
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Towing our 5er, I once got 7.4 or there about. It was extremely windy. That was the mpg I got for the whole tank. The next tank was not much better. Winter blended fuel does not help either. I do know that when towing, I get my best mpg's in the 62-65 mph range. Another idea is this. I do not think all diesel fuels are created equally. Yes, it may be diesel fuel, but when I'm home, and get diesel fuel from our propane supplier, it is 50 cetane, bio free, premium diesel fuel. Truck really likes that fuel. Could you have gotten a tank that had a higher bio percentage, than the previous tank. I know fuel is suppose to be fuel. In our travels I have better mpg with FlyingJ fuel over Loves fuel.
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post #5 of 43 (permalink) Old 03-19-2017, 09:25 AM
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Lots of variables. Weather conditions, wind, if you are headed north you may be getting that crappy winter blend fuel. How long has it been since the fuel filters and air filter were changed?

Also you may have a brake dragging or a bad bearing on either the truck or trailer. That would kill mileage.


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post #6 of 43 (permalink) Old 03-19-2017, 12:28 PM
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A good friend is a diesel fuel sales guy. He says that the blended fuels with bio does not have the power of true petroleum diesel. Many independent stations push the limit of bio to make more money.

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post #7 of 43 (permalink) Old 03-19-2017, 02:07 PM Thread Starter
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Quote:
Originally Posted by Redthies View Post
Did you go from the Transforce to Super Swampers?? That would kill a couple of mpgs!
LOL, no i went from oem 235 80 17 Nexen to 235 80 17 Nitto EXO Grapplers. I started getting the bad mileage while on my oem nexen tires then last week i put the EXO's on and crap mpg stayed the same at about 7.4 mpg. Before i always got 11mpg where we go camping but all of a sudden when my truck hit 20,000 miles on the odometer it went to crap to 7.4mpg.
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post #8 of 43 (permalink) Old 03-19-2017, 02:10 PM Thread Starter
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You could have picked up the last of someone's the winter blend, besides you are towing heavy with a head wind 7.5 could rapidly happen. Have you analyzed the oil recently?
Just changed the oil about 1500 miles ago for the 4th change. Yes i have done 2 oil analysis with Blackstone they were normal results. No more head wind than usual either. This is our 3rd trip with the same crap mileage.
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post #9 of 43 (permalink) Old 03-19-2017, 02:42 PM Thread Starter
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Towing our 5er, I once got 7.4 or there about. It was extremely windy. That was the mpg I got for the whole tank. The next tank was not much better. Winter blended fuel does not help either. I do know that when towing, I get my best mpg's in the 62-65 mph range. Another idea is this. I do not think all diesel fuels are created equally. Yes, it may be diesel fuel, but when I'm home, and get diesel fuel from our propane supplier, it is 50 cetane, bio free, premium diesel fuel. Truck really likes that fuel. Could you have gotten a tank that had a higher bio percentage, than the previous tank. I know fuel is suppose to be fuel. In our travels I have better mpg with FlyingJ fuel over Loves fuel.
We also thought maybe a bad tank of diesel but i use the same Exxon as always and its a big nice truck stop, but that doesnt mean it wasn't some junk diesel. We don't really have bio diesel anywhere around me.
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post #10 of 43 (permalink) Old 03-19-2017, 02:54 PM Thread Starter
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Originally Posted by Highway 4x4 View Post
A good friend is a diesel fuel sales guy. He says that the blended fuels with bio does not have the power of true petroleum diesel. Many independent stations push the limit of bio to make more money.
We don't have Bio anywhere around us. Think I'll replace the air filter maybe that thing has a rats nest in it. I just returned from a 375 mile round trip camping trip. Same thing, got 7.5mpg no wind or rain on same rolling hills as always with 6th locked out doing 65mph. Something Weird is going on. Wished i knew if it was stuck in regen cause that would explain it.
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post #11 of 43 (permalink) Old 03-19-2017, 03:12 PM
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Put something with a cetane booster in it injector cleaner and see if it helps and or switch gas stations.

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post #12 of 43 (permalink) Old 03-19-2017, 03:25 PM
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Quote:
Originally Posted by Rebel Horseman View Post
Lots of variables. Weather conditions, wind, if you are headed north you may be getting that crappy winter blend fuel. How long has it been since the fuel filters and air filter were changed?

Also you may have a brake dragging or a bad bearing on either the truck or trailer. That would kill mileage.


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For a brake to do that to mileage, there would be brake smell, smoke, etc.

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