Engine/Transmission (1994 - 1998) average mpg?

[JesseGray]

On the old Detroits, you used to have to do all your work between 1800 to 2100 rpm. That is where I try to keep my Cummins. I may be one old foogeys, but I have driven bigger than a Honda.



My 97 turbo does not start to kick in until 1700, so at 1500 I am in fourth with my trailer. I seem to have plenty of boost after 1700 but the power seem to be not all that plentiful. At 70 mph Im pulling 12 boost and my egts are 700.

 

[J.BURCHFIELD]

On the old Detroits, you used to have to do all your work between 1800 to 2100 rpm. That is where I try to keep my Cummins. I may be one old foogeys, but I have driven bigger than a Honda.



My 97 turbo does not start to kick in until 1700, so at 1500 I am in fourth with my trailer. I seem to have plenty of boost after 1700 but the power seem to be not all that plentiful. At 70 mph Im pulling 12 boost and my egts are 700.

I have driven the old detroits too. They were 2 cycle engines and got their power wound up. Our Cummins are 4 cycle (what a diesel should be) and peak torque comes in at 1300 to 1500. I have a Gear vendor so at 70 I am doing 1500 RPM and EGT is 700 not towing. Don't pay much attention to boost.

 

[fest3er]

I'm begining to think it's all fuel related. I get between 15 and 20, should not very that much. I asked a local fuel hauler what the cetane of his fuel was and he said 40. Every spring I seem to get better mileage fore a few weeks I think it's because they are putting better grade fuel in the tanks to get rid of winter blend, then it goes back down.

I can guarantee it's related to fuel. Specifically, y'all need to be running a double-shot of of cetane boost and lubricity enhancer with ULSD. First, ULSD's cetane is so much lower that fuel economy suffers. Second, not all fuel distributors add enough (or any) lubricity enhancer to the fuel before they send it on to filling stations. Heading to Vegas and back to VA, I found that I got the best mileage when I started using Power Service additive with Stanadyne. Stanadyne's newest formulation probably has very good lubricity, but it didn't do much for power. Using a double shot of two different additives should pert near guarantee that you have enough lubricity for the fuel system, and enough cetane to get decent fuel mileage.



Heading to Vegas towing a 12' 3000# trailer, I was getting 13-14 MPG, running 70-75 most of the way. Heading back, I was getting a little better than 14. When I dropped the trailer in IN, I was back to my usual (pre-ULSD) 18-18. 5 MPG at 75 MPH.



Another thing to note is that Stanadyne's old additive formula really does have a limited shelf life. The new ULSD formula is supposed to be good for a much longer period of time. So other additives may also have a limited shelf life.



I'm beginning to think ULSD was EPA's way of retarding injection timing, thus reducing the production of NOx *and* increasing fuel usage to keep the oil companies happy. Mayhap bumping your injection timing up by 3-5 degrees might 'restore the balance'.

 

[ddechris]

Well, we finally got a good highway road trip in on the truck to get some mileage numbers. Over 2400 miles, the best corrected mileage I got was 20. 5 mpg. Most tanks were in the mid 19's.



There was a Hi-top cap (shell) installed filled with camping gear. Overall, the truck weighted about 7900 lbs. I have the tow mirrors, and I can hear them whistle, so there is some extra resistance there. Anyway, we drove from PA down Route 81 through Virginia, Route 40 and 75 in Tennessee and then out Route 59 in Alabama and Mississippi. I am running 265 tires pumped to 70 psi. Using mile markers, this gives a 5% overdrive compared to the factory 245's.



The first half of the way down I was running 65 mph on the speedo which was closer to 70 once I figured out the correction. That leg was a little mountainous with the boost gage cycling from 3-10 psi with the cruise set. The second leg was much flatter, but posted 70 mph which means we were doing 75 actual. That was the worst tank. I also noticed the doors vibrating which I chalk up to the wind resistance of the tow mirrors. Anybody else notice this on a quad cab?



The return trip we did better because I was running the actual speed limits. That is where I got just over 20 more consistantly.



I was definitely pleased to make 20 mpg, but I think this truck should be capable of more. Either it needs more timing or it's the 300 injectors don't have a decent spray pattern. I suspect that my mixed driving is low (15-16) because most of it hovers around 45 mph where the torque converter is constaintly jumping in and out. I might put a disable switch in for local driving and see if that makes a difference.



For hauling an extra 3000 lbs, it beat the 1/2 ton Chevy we took out west 2 years ago. And I really had to smile when I saw diesel for $2. 63 while gas was still up near $3.



- Dave

 

[ddechris]

Just had another quick thought on this topic: Tire width.



My brother has a '93 1st Gen and he claims to get 20 in mixed driving and more on the highway. He runs 235/85's.



Could the higher mileages be more a tire factor that anything (secondary to 2wd vs 4wd of course). The wider the tire, the more rolling resistance? Might that explain why duallys do so well since they are limited in tire width?



Anybody have a fat tire that is getting high numbers?

 

[DonTX]

You could just be on to something correct there. My great mileage is with the very skinny original width tires.

 

[J.BURCHFIELD]

Well, we finally got a good highway road trip in on the truck to get some mileage numbers. Over 2400 miles, the best corrected mileage I got was 20. 5 mpg. Most tanks were in the mid 19's.



There was a Hi-top cap (shell) installed filled with camping gear. Overall, the truck weighted about 7900 lbs. I have the tow mirrors, and I can hear them whistle, so there is some extra resistance there. Anyway, we drove from PA down Route 81 through Virginia, Route 40 and 75 in Tennessee and then out Route 59 in Alabama and Mississippi. I am running 265 tires pumped to 70 psi. Using mile markers, this gives a 5% overdrive compared to the factory 245's.



The first half of the way down I was running 65 mph on the speedo which was closer to 70 once I figured out the correction. That leg was a little mountainous with the boost gage cycling from 3-10 psi with the cruise set. The second leg was much flatter, but posted 70 mph which means we were doing 75 actual. That was the worst tank. I also noticed the doors vibrating which I chalk up to the wind resistance of the tow mirrors. Anybody else notice this on a quad cab?



The return trip we did better because I was running the actual speed limits. That is where I got just over 20 more consistantly.



I was definitely pleased to make 20 mpg, but I think this truck should be capable of more. Either it needs more timing or it's the 300 injectors don't have a decent spray pattern. I suspect that my mixed driving is low (15-16) because most of it hovers around 45 mph where the torque converter is constaintly jumping in and out. I might put a disable switch in for local driving and see if that makes a difference.



For hauling an extra 3000 lbs, it beat the 1/2 ton Chevy we took out west 2 years ago. And I really had to smile when I saw diesel for $2. 63 while gas was still up near $3.



- Dave

16,17 and rarely 18 combination city and interstate driving. On a trip I have done much better but that has been a while. May go on a long trip next month and will know more then. Air filters must be clean/changed often and the engine looked after to get the best milage. My pump (98 12v) has been calibrated, valves adjusted and the timing never touched. I have seen 20 MPG a long time ago. I am encouraged by what you wrote. With the change in diesel fuel to less sulfur I am wondering how much mileage is affected. I suspect it won't be much if any. My 265's (Michelin @ 70 psi) going by mile markers showed 96 miles on the trip odometer when I traveled 100 miles by the markers. So I figure 4%. If I go 400 on the odometer I use 416 to calculate milage. Not knowing how accurate our mile markers are your 5% may be more accurate than my 4%. Here in Florida there does not seem to be much pride in workmanship (I am from Ohio) just slam bang get it done and go fishing.

 

[Ahopper]

just got back from a trip to mexico pulling a two place ski trailer around 1500lbs and my truck was empty i got 19. 5 at 75 mph on mexican fuel. my boost still seems a bit high 10psi and up. and my egt wouldnt go below 950* but it was 108* outside so that might be a factor. on my way there doing the same speed and milage i got 18mpg. that was on the ulsd. i dont think mexico had this emission crap like we do so im figuring it wasnt ulsd and that is why my milage went up? also im running 295/75/16 with a leveling kit on the truck so its around 11. 5inch wide i belive and 33. 9 inch tall i think?

 

[DonTX]

Down in this part of the country, the prevailing winds blowing north would have been a reason.