fuel milage drop

[muddyduck]

I was wondering if anyone else experienced the same problem i have. I recently changed out the muffler for a flowmaster 4" (24 inches long) and on the last two tanks i went down from 18. 3 average to 12. 2 hand calc, not towing anything. does anyone have any idea what could have caused the drastic change. I did have the tsb done for the white smoke and improved fuel milage. I have not modded this truck yet other than the exhaust. thanks for any help...

 

[PJ]

Have you checked your fuel filter lately? Also, I know in my area they just switched to "winter blend" diesel. That will screw up your mileage by 2 or 3 mpg's :{

 

[Kennywould]

I wouldn't think that a muffler change would make a 6 mpg difference especialy to the worse. PJ might be right about the fuel filter, how many miles since you changed it, check the air filter also, have your fuel pressure checked if you don't have a gauge to monitor it.

 

[rbattelle]

You're talking about a 66% (2/3) drop in fuel economy! That's ENORMOUS! There is definetly something fishy going on here.



All else being equal, the simplest answer is usually correct: are you sure your calculations are accurate?



-Ryan

 

[GOTSOOT]

why would you put a gasser muffler on ?

 

[muddyduck]

checked with flowmaster and according to them there is not a exact muffler that is assigned to that truck. they gave me a very short list of mufflers that will work great. I really like the sound, not too loud and not too soft... just right. . thanks for the response gary

 

[JCleary]

I just had a Banks exhaust and AFE intake installed. My mileage has dropped about 2 mpg.



The answer:



I love the sound, so I'm on the throttle more and revving it out more, hence the mileage drop. I also have a KORE suspension, but the tires are the same as before, BFG 285's (for now).

 

[MYamamoto]

I don't have an answer for you as to why your mileage dropped, but if anyone else has an idea as to what would cause it, I am also all ears. My truck did about the same thing as yours did. From the day I drove the truck out of the dealership, I would get about 20mpg out on the highway and about 15 in town. When I changed my exhaust system and made a trip with only the truck, it dropped down to 13. 9 :--) After being very frustrated and several more trips to see if it would improve, it didn't. I put the factory system back on and made a few trips to see what the results would be. Surprisingly my mileage came right back up to 20mpg. After more work crawling under the truck I put the aftermarket system back on and my mileage when back down to 13. 9 grrrrrrr... ... The motor seemed to have more power and the turbo would spool up a lot quicker. When towing my egt's were quite a bit lower so I ended up leaving the aftermarket system on there. I now have 80,000 miles on the truck and my mileage has come up to 17-18 but still can not get back up to the original 20mpg. As for mods to the truck, the actual motor has not been touched. I have an AFE Intake, 5" exhaust system and a US Gear Exhaust brake. Everything else is stock. Any ideas would be much appreciated.

 

[GHanna]

"You're talking about a 66% (2/3) drop in fuel economy! That's ENORMOUS! There is definetly something fishy going on here.



All else being equal, the simplest answer is usually correct: are you sure your calculations are accurate?



-Ryan"



More like around a 33% drop. 66% would be about six mpg!

George

 

[rbattelle]

"You're talking about a 66% (2/3) drop in fuel economy! That's ENORMOUS! There is definetly something fishy going on here.



All else being equal, the simplest answer is usually correct: are you sure your calculations are accurate?



-Ryan"



More like around a 33% drop. 66% would be about six mpg!

George

Sometimes I hate being a moron.

 

[SLinse]

I'm jumping on the ship... . Mine was also getting 19-20, with a diamond eye 4in exhaust. Now I'm down in 12-13 range as well. I'm not sure when exactly it happened, I know it was this summer dropped, and now on the winter fuel it dropped more. I have taken it in to the dealer and they tell me everything is normal. I was thinking about checking the valves. I know they say no need till 100,000. However, you just never no!

 

[WarrenSims]

i pulled a 30 ft 5th wheel from florida to kentucky and never seen transmission temps above 180 on my transmission guage and my senso is in one of the plugged off holes on the transmissin that is always submerged in fluid. ( that was with overdrive activated) not tow haul mode and i was running the edge ez on max setting... ..... EGT temps are your biggest worry . I've been at 1400f several times and no problems yet. averaged 14. 5 mpg with the rv going 65 and 70mph. for you guys with mpg on the 600 motor issues i get 16. 5 in town with the edge set on max and the latest tsb flash done. . the tsb flash gave me about 1. 5 mpg better fuel mileage and i get 21 mpg running empty on the interstate at 65 wich means i'm actually going 70 mph with my 315 bfg's mounted.



2004. 5 cummins 600 auto 4 door 4x4 373gears