2003, 14mpg

[JCafferty]

I just completed a trip from Eastern Washington through Montana and Wyoming. During the trip the mileage was the worst I have ever recorded, 14. 6 mpg. Even when pulling 4 horse up 6% grades my mileage isn't this bad!



My truck is a 2003, 3500, single real wheel, 6 speed that I bought new in July of 2003. The truck is all stock except I am running 35/12. 50 Toyo Open Country tires. The tires have hurt the performance a little but this mileage is unreal. I was admittedly gaining some elevation and driving between 80 and 85 mph, but the worst I ever get on the highway is 20.



Was the high speed and resultant 2500 rpms the culpret or is there something else wrong, and if so what. Has anyone else seen this type of extreme fuel consumption at high speeds?

 

[DaveHess]

I know I am going to flamed on this one but 85 MPH is a little excessive to expect decent fuel mileage. I mean nothing personal to JCafferty by that. Here is a breakdown on my '03: (All approximate mileages as they were done in 2004) 55 MPH-24 MPG, 60 MPH-21 MPG, 65 MPH-19 MPG, and 70 MPH- 17 MPG. My trucks weighs 7640 with me in it (local CAT scale). All trips were a 180 mile loop (4x) filling at the same fuel station from the same pump using the same method of fueling. Trailering on average nets me 10 to 12 with a combined gross of 17,080 going 65 MPH. So, if we were to put this into some form of perspective and trusting the validity of my tests, 14. 6 at 85 MPH is probably in the ballpark. And please, nothing in this post should be construed to be a personal affront to JCafferty. Just my personal observations relating speed to mileage.

 

[hearingyourlies]

2 things ... first, if you want better mileage, slow down.

Second, was that hand calculated or according to the computer and has your speedo been adjusted for the larger tires?

 

[ASchwartz]

was that hand calculated or according to the computer and has your speedo been adjusted for the larger tires?

my thoughts exactly

 

[JCafferty]

The speedo has been recalculated, and yes I know that driving faster is going to bring down my mpg. This was hand calculated mileage.



I was on my way to an unplanned funeral, and honestly I rarely if ever drive much above 75. My mileage has just recently been decreasing, likely due in no small part to the oversized tires. The issue was just driven home by the big drop in mileage. As I mentioned earlier 22 to 24 is what I normally get at highway speeds, 75 to 80.



Even after I got back onto 2 lane roads and was driving between 60 and 65 with my rpms under 2000 I never got over 18 mpg. Before I bring it into the shop and start throwing money at them (since I don't have any to spare) I was hoping that I could try to pinpoint the problem.



Everything on the truck is still original except the tires that I put on 2 years ago. It has almost 90,000 miles on it. I had the pressure checked on the in-tank lift pump and it was performing within limits less than 20,000 miles ago. Injectors are stock, air cleaner is stock, clutch is stock, just changed the oil, diff fluids have been changed and all routine maintenance has been performed. I don't use additives in the fuel during the summer, but do in the winter.



Aside from rushing off across the west at higher than normal speeds not much has changed except fuel consumption.

 

[GaryOwen]

Seems like most likely mileage killers in your case is speed, tire size and tread pattern, and ULSD fuel. With the low miles you have on the truck, I wouldn't think injectors would be suffering from wear, but could have partially plugged injectors. I would try running some Power Service Diesel Kleen (silver bottle). Seemed to help my 03 to give it a dose every 5k miles or so. Check your codes also.

 

[JJPage]

I have run between Spokane and Helena numerous times, usually at 70mph with the occasional bump to 75mph, never have quite made 19mpg. On some of my more hurried trips(same route) 80mph+, I have been down to 15/16 mpg range. This is all hand calculated, similar to your route JCafferty, so I do not believe your mileage is out of line.



I am not positive, but with us having fairly close, the same diameter tires(mine are just shy of 35"), me having an auto vs your 6sp, you are probably turning more R's in 6th than I am in OD, further hampering your mileage.



I hope someday I reach 20mpg, but with mountain passes in almost every direction, might be difficult.



Now with all that being said, when my rail relief valve was leaking, my mileage went to hell. So you could have a fuel delivery problem starting to develop, rail relief valve, lift pump, fca, injector(s), all something you can investigate.



Jess

 

[Andersonville]

Use fuel additive year round

 

[AHofner]

Have you replaced/cleaned your air filter lately? Seems to be often overlooked, but could explain the poor MPG.

Good luck

 

[NavyDood]

Change air filter and fuel filter and then dump a whole quart of PowerService white bottle in it and run it.

 

[ray1933]

2003 Mileage

Hand calculated with no load, 65 to 70 mph 17 to 18 mpg and the overhead reads 21 to 22.



Pulling the 5th wheel with no head wind,, through the Blue Mountains and down

the Columbia River Gorge to Dufur, Or and back to home the same route it is 13 mpg.

Have made the same trip with a 35 to 40 mph head wind and it was 8 to 9 mpg. This is with cruise set at 65 with OD on in the flats and OD off in the Mountains.



When I say hand calculated,, that means I fill the tank myself to the lip of the filler spout each time so I know it is correct.

If a a person wants you can get just about 5 gallons in the tank after the automatic shut off on most pumps.



I sure do not know how you get over 20 mpg gallon with an automatic.



I did that with my 95 Stick shift on a regular basis.



Our first Dodge was a 91 with the automatic was lousy empty and worse with the 10 foot camper.

 

[DaveHess]

Ok, since yesterdays post (#2), I ran to Dickinson, ND (189 miles Round Trip) at 75 MPH. I did the test routine of same fuel stop, same method of filling, etc, and hand calculated the mileage. 16. 2 MPG with a 12 mile section of construction on I-94 reducing my speed to 65 for that period. So 24 miles of the 189 at 65. Seems on par with my previous test of 17 something at 70 MPH. My tires are factory original and I have run Stanadyne Performance Formula since the very first fill-up and have never missed a fill-up. I still think given your combination JCafferty and the speed, that your mileage is not out of line. As for the funeral, sorry for your loss.

 

[TCDiesel]

Fuel additive?,MN has 5% mandatory Biodiesel, Take one Gallon of MN fuel and ad 1oz of additive leave sit for 48hrs... You will see the nice clear/Yellow color turn green and solid material will float on top, do this in -0 temps and it the... ... Now I can't speak for fuel in other States, But I would be calling the chemist at the correct refinery and get his input before adding and type of additive.

 

[JCafferty]

Thanks

Sounds to me like I had better just shut my mouth and be happy with the mileage I did get.



Like I said before I don't ever drive this fast, and I haven't taken the truck on any trips with the new tires before, except to go up in the mountains pulling a loaded 4 horse trailer.



Conclusion, keep the rpms under 2000 and get some skinny tires. Thanks for all of the imput, ideas and help.

 

[JCafferty]

I have run between Spokane and Helena numerous times, usually at 70mph with the occasional bump to 75mph, never have quite made 19mpg. On some of my more hurried trips(same route) 80mph+, I have been down to 15/16 mpg range. This is all hand calculated, similar to your route JCafferty, so I do not believe your mileage is out of line.



I am not positive, but with us having fairly close, the same diameter tires(mine are just shy of 35"), me having an auto vs your 6sp, you are probably turning more R's in 6th than I am in OD, further hampering your mileage.



I hope someday I reach 20mpg, but with mountain passes in almost every direction, might be difficult.



Now with all that being said, when my rail relief valve was leaking, my mileage went to hell. So you could have a fuel delivery problem starting to develop, rail relief valve, lift pump, fca, injector(s), all something you can investigate.



Jess

Jess,



Do you perform all of your own work? I'm over in CDA and looking for a shop.

 

[DaveHess]

Fuel additive?,MN has 5% mandatory Biodiesel, Take one Gallon of MN fuel and ad 1oz of additive leave sit for 48hrs... You will see the nice clear/Yellow color turn green and solid material will float on top, do this in -0 temps and it the... ... Now I can't speak for fuel in other States, But I would be calling the chemist at the correct refinery and get his input before adding and type of additive.

TWest, That whole mandatory Bio thing in MN is why I'll top off in Jamestown, ND and not fuel again until WI. Gotta love 500+ mile ranges. I'll have to try that fuel test with ND fuel and see what happens. This could be fun!

 

[JJPage]

Jess,



Do you perform all of your own work? I'm over in CDA and looking for a shop.

pm sent!!!!

 

[AMcCormick]

my last tank came out to 17. 41 mpg, today. This is with a few hundred pounds in the bed and very little extended highway driving. I am only on the freeway for short distances so my average speed is a bit lower. Since Jan my best tank has been 20. 76 and worst of 15. 93. Mostly in the 17-18 range. I change the oil, filter and air filter every 5k and fuel 10k.

 

[MickeyMiller]

My experience agrees with Ray1933... 22 mpg overhead = 18 mpg actual. I consistently run 18. 2 mpg hand calculated with about 60% highway and staying at 70 mph on the highway. I can pick up another 1 mpg on secondary roads running at 60-65 mph, plus the scenery is better! I like Hwy 50 way better than Hwy 80 for my east/west trips!

 

[KIKER]

My '07 3500 DRW Quad auto 4X4 gets 12 mpg. I drive 53 miles one way to work, 65 mph in the morning and 70 going home. It weighs 11,700 going down the road with all my tools in it. It got about 11 mpg the first fill up and then 12. I have 60,000 miles on it and it has never gone over about 14. 5. It is a 5. 9 and I have been running Smarty Jr. on 1 and 2. AFE drop in air cleaner. Not too happy with it. My '99 4X2 5-speed got 16-19 with the same tools.