[Thatrooper515]

Hey guys, I'm curious about my poor fuel mileage, and if I have some underlying problem causing it or if it's just normal.
2008 f350 srw. Guessing it's geared 4:10? Straight piped. Egr completely deleted. Sct x4 tuner with custom tunes from a local shop. They said the race tune would give the best results but I usually run the tow tune since I'm pulling daily. Running 315/70-r17 all terrains with a leveling kit.
If I baby it in the race tune no trailer I get 12-13mpg, pulling in a tow tune or being a little more aggressive with the gas pedal in the race tune I get about 10-11.
Is this normal? I figured a programmed and deleted diesel should get at least 15. Poor injectors or something? New to diesels so I'm very ignorant here. Would appreciate any input.

 

[ArcticDriver]

Did they mention why your best fuel economy would occur in a "race tune"?

 

[ptanner3]

deleted 08 drw I average 12-13 towing or not

 

[wingnut60]

Have you accounted for the increased diameter of the 315s? That could be part of it. 315 has about 8% fewer rotations/mile. Did you change the tires same time as the tuner? Accounting for the revs/mile, still sound a little low--my tuned 450 w/4.30 gears weighing 10klbs gets about 13 around town, 14 on hwy. You may not have 4.10 gears, maybe 3.73, not sure about that.

 

[Thatrooper515]

They didn't mention why the race tune would be the most fuel efficient just said it would be if I drove it right.
And yes it was tuned with the bigger tires. Just thought I should be getting better mpg than what I am.

 

[wingnut60]

I'd say it has something to do with your driving habits--doesn't take many 'bursts' of throttle to keep the mpg low, and hard not to do that even on the tow tune.
I run my MiniMaxx on street tune most of the time, never on performance. On tow or stock tune when towing my heavy fiver--I drive exclusively by EGT when towing--too hot and I get out of the throttle, or downshift and slowdown.
From my experience, it is hard not to step out from stoplights when the truck has such great response, but no matter what I do--try to get good mpg, or run it at 70-75, it usually gets 13-14 pencil figures. Can't pay attention to MPG data, too optimistic. Have seen lots of 17-19 on the dash, only to figure it out to 13-14.
Don't know what else to say...hope it gets better for you.
Joe

 

[Thatrooper515]

Maybe my foot is a little heavy...I bought the truck expecting at least 15 once I was tuned and deleted. May have had expectations a little high. But performance wise what else can I do to improve fuel mileage? And no I'm not losing my big ole tires. I was planning on running a fass fuel system. And maybe injectors next. As well as down pipe and 5in exhaust instead of my 4in I have now. Not sure if any of that will help me any.

 

[drewactual]

Maybe my foot is a little heavy...I bought the truck expecting at least 15 once I was tuned and deleted. May have had expectations a little high. But performance wise what else can I do to improve fuel mileage? And no I'm not losing my big ole tires. I was planning on running a fass fuel system. And maybe injectors next. As well as down pipe and 5in exhaust instead of my 4in I have now. Not sure if any of that will help me any.

none of that will help you.

decreasing rolling resistance will- both contact patch and wind resistance.

the higher the performance tune, generally, the greater the economy so long as you stay off the skinny. easier said than done, no? it comes down to less effort of the engine to get the inertia moving and keep it moving by more fuel being delivered on an advanced timing curve (pilot injection) and then chasing the piston after TDC. the piazio injectors allow up to five injection events per cycle- they're pretty quick, no? five squirts at optimal points of the right volume is better than one of the same volume at not as precise a time... one starts the burn, then more is added, but not so much that you'll see clouds of soot behind you- because it's mostly being burned inside the cylinders as opposed to in the exhaust. the volume is important, the timing of initial burn is important, and the timing of the last is important.... most of the race tunes light it up early with the pilot, then chase the piston- a bit more volume, but producing hella torque- which gets you moving with less effort. tracking?

check your brake calipers... these things like to hang up a bit at times, creating drag that will kill economy... easiest way to check is to chock other wheels, then jack wheels up one at a time in neutral and give them a spin... you'll be able to judge when it 'should' stop spinning based on it's decreasing speed (it should be linear), but if it stops premature to that it isn't free rolling- hence, it's doing the same thing and more compounded when the weight of the truck is on it... and economy takes a nose dive... this, to me, seems to be the greatest mechanical factor between rigs used similarly and in similar environments... the caliper hug is all too common...

 

[Thatrooper515]

Thanks for the detailed response! I'm certain I have some kinda issue with my brakes. Mild leak from the driver side rear. Haven't had the time to check it out but totally forgot to check for a locked caliper. Hopefully I'll find some time this weekend. Maybe then I could see 15mpg.

 

[wingnut60]

While working on the brake, check the tag on the diff for what ratio is in it--just to get that out of the equation. With larger tires, the lower numbers work against you.
If you get an honest 15, let us all know--it should be doable with a SRW.
Joe

 

[Thatrooper515]

Discovered both rear had those pins seized up on the caliper. Had to replace one bracket and got new pins on both. Went ahead and cleaned the bores and greased the front pins. My "lie o meter" is already climbing on mpg. Gonna be hauling a lot this week but should see some improvement. Good call on those. My 08 f350 v10 never had that issue!
Forgot to check the dif for gear ratio. Will do that at some point. I'll post what kinda mpg I'm getting once I burn through a tank. Still praying for 15 when empty. Thanks guys.

 

[hillbilly2354]

Was it the front or rear brakes? My front rotors get very warm compared to rear, what if I have a limited slip how could I check those? I have a 2008 6.4 deleted and tuned with Spartan tunes gets 10.5- 11.5 city very consistently and 11.5-12.5 highway. I have 6 inch lift 35 inch tires and 410 gears been gettin real tired of 10 mpg would love 15 any more recommendations? I cleaned the mat sensor it was pretty dirty but don't think I got much out of it..I run synthetic oil and boost usually seems high! Even with my foot out of the throttle I've differnt driving patterns without much success maybe 1 mpg except freeway I usually set the cruise at about 75 -78

 

[drewactual]

what kind of temperatures do you see? coolant?

one thing is for certain- warmer gets better mileage... if your thermostats are tired, and you stay below 194, you're going to pay for it at the pump... 195+ gets better fuel economy...

I'm seeing lower ect's with my rig lately, and I know the 'stats are about to give up the ghost.. I gotta run it marginally hard to see 196... My next 'stat pack will be 205* stats... I'm going to try to make it through the summer with the OE stats, and load the hotter ones in the fall... and watch my mileage skyrocket..

 

[yan7gin]

not sure if its been said and I miss it but look at you EBPS and tube make sure its nice and clean. plugged tube will affect the fuel economy. Race tune are normally not the best for fuel economy because they dump lots of fuel a low RPM to get the power. best would be to get a nice DD tune or probably the Tow tune would be better than the race one.

only my .02

 

[ArcticDriver]

what kind of temperatures do you see? coolant?

one thing is for certain- warmer gets better mileage... if your thermostats are tired, and you stay below 194, you're going to pay for it at the pump... 195+ gets better fuel economy...

I'm seeing lower ect's with my rig lately, and I know the 'stats are about to give up the ghost.. I gotta run it marginally hard to see 196... My next 'stat pack will be 205* stats... I'm going to try to make it through the summer with the OE stats, and load the hotter ones in the fall... and watch my mileage skyrocket..

Drew,
The RT-1212 thermostats are rated at (EDIT: 190*)
Why would you wait to install if your fuel economy will "skyrocket" ?

I have never found any test results that support your claims. How did you come to these conclusions?

Not wanting to argue...just wanting information.

Thanks

EDIT: OE are 190*.

 

[hillbilly2354]

My stats are oe and they are almost always 190-194 I thought I read somewhere that is what it's suppose to be at, but I would def move up to 205 if it got better mpg.. And just clean with brake or starter fluid om the ebps?

 

[drewactual]

Drew,
The RT-1212 thermostats are rated at 192* and 203* ?
Why would you wait to install if your fuel economy will "skyrocket" ?

I have never found any test results that support your claims. How did you come to these conclusions?

Not wanting to argue...just wanting information.

Thanks

Mishimoto has made a 205* stat, and all reports are they increase mileage....

 

[hillbilly2354]

But where's the info to back it?

 

[ArcticDriver]

My stats are oe and they are almost always 190-194 I thought I read somewhere that is what it's suppose to be at, but I would def move up to 205 if it got better mpg.. And just clean with brake or starter fluid om the ebps?

Hillbilly. Sorry, OE is RT-1212 and is rated at 190* only.

 

[hillbilly2354]

And the higher temp helps gas mileage?