In the last month or so, my mileage has been taking a nose dive. I went from 17-18 down to 12.5-14.

The only changes i have made have been the addition of the Fass, having to use Delvac this last oil change rather than Mobil 1 synth AND I have been experimenting with adding some 2 stroke oil to my fuel. My transmission has been acting up as well, but it gets replaced tomorrow morning. None of this seems as if it would have such a negative effect on my mileage. BTW- Injectors seem fine. The only other out of the norm factor I can think of is that it has been brutally hot here for the past month.

Any clues as to what it could be? I love my truck to death, but it's really not practical at 12.5 mpg empty. It's picking a fine time to act up on me, because I have dumped a lot of money into the Fass and the Suncoast.

 

Could all be in the trans, inefficiency/slippage can kill your mileage.

 

Stock tires/rims?

 

I think the Tranny might me it also but!!!! when i tried the 2 smoke oil my MPG went DOWN!

 

ULSD? I see a -2 mpg when I use that compaired to LSD.

 

i just checked my truck out cause i was getting crappy mileage- all 4 tires were about 20 psi low.... hopefully that helps my mpg.

 

So did mine by almost 1 mpg. But it is most likely the transmission as the biggest problem.

 

Ouch, that will do it too............ Been there myself with other vehicles

 

Im feeling your pain, Im having the same issues. Changed my filters a couple weeks ago and my milage went from 16-17, to 13-14 and Im still bone stock.

 

I have the 285 Cooper STT, but I have had them on there a while now and they are properly inflated.

ULSD is all I have used since last year. I think it's strange that some others here have experienced a recent drop in MPG for no real reason, especially the guy in KY.

I'll have my new transmission in tomorrow. I will fill up and check my mileage and report back as soon as I get enough info.

 

i have a 6 spd 2004 3500 dulley four wheel drive truck. When i first bought the truck brand new, 19-21 mpg highway was normal. now it is 13-15 highway and pulling a enclosed 24 ft trailer i get 7-9 mpg. it started when the dealer put a new clutch in it. They took it back and ran it through the computer and they said everything was ckecked out fine. At 70 mph it starts to rumble in the dash but it isn't the barrings, tires, etc. It sounds like the exhaust is plugged???? any sugestions???

thanks big D

 

Check you air filter. If it's dirty mpg will take a nosedive. My 'restriction gauge' has been pretty reliable - as soon as it goes half way down, my mpg goes down at least 1 - 2 mpg.

 

Good idea! I will check it, but it's an AFE filter in the factory airbox. I think it should be fairly clean as it's only been in there about a year.

 

maybe your kitty is plugging up?

 

If you are saying that you have an AFe filter that has not been cleaned in a year I would definitely clean it and hope for improvement. Best of luck regardless.