My overhead read about 16.7 to 16.9, but actual mileage was only 14.2, on stock size tires. Most driving was short trips and basically no highway miles. I know that's not TERRIBLE numbers but I am hoping to get up there around 17-20 mpg if possible. I was using the overhead to adjust my driving style and it seemed the harder I accelerated (to a degree) the mileage went up, so I would try to drive it harder, I think this tank I will ease up and see what happens. But other than that, I need to fix a small fuel leak behind the motor. I think it's the stock return line but haven't pinpointed it yet. Some ideas of future upgrades are AFE Stage 2 intake, RV275's, maybe a larger intake horn? Besides that, all pumps and fluids are fresh, so what else can I look into for mileage and performance?

  JOHNFAK said:

Mike - was towing on 95s to Florida - Very Flat. Thought I'd try your theory of slowing down. Dropped about 8-10 mph from 65-68 down to 58 ... No net gain in mpg after 250 miles ..,. About 12.3 towing .... Any thoughts ?

Do you have "gauges" in your truck??? If so, what were the reading prior to slowing and after??? I drive by the boost gauge and the EGT gauge; and I try to keep them as low as possible. Without lugging the engine of course. Since this is a 2nd gen forum........do you have 3.55 gears in the rears??? What were you towing?? Was it big??? If so, you may have been out of the "sweet spot" of your truck. That's why I asked about gauges. They tell you so much about your right foot!!!

I don't see anything wrong with owning a truck and still wanting it to be as efficient as possible... I mean, if I had come on here asking how to get 30mpg's out my 8000lb. truck, I could expect some critism...But anyways, this is turning out to be a pretty useful thread, I'm just going to sit back and soak up the information for now. I need to fix the leak before I start to think about spending money on upgrades.

My details in my signature. The 4.10 gears are NOT the way to go unless you are going to add big rubber. My impression is that those with stock ratio tow just fine. That said, I can milk 18 out of her on RARE occasion when I run empty on the sweet spot... but it's rare. Keeping in high gear at 40-50 mpg, light on the pedal... Towing? All bets are off. The trailer, windage make a huge difference... though even a light trailer like my landscaper's trailer does make a noticeable difference. As a comparison... my old reliable C30/454/tow cam/Edelbrock intake/AFB/headers/automatic/3.73 final ratio/16.5 wheels. It got 11 mpg on Reg Gas. Towing/Empty did not matter. The only thing that mattered was the AC which stripped off 1 mpg. From what I know, the right final drive ratio & more transmission gears help. I see this in new cars. I wonder if retrofit transmissions for our trucks will emerge?

  02cumminsdude said:

I don't see anything wrong with owning a truck and still wanting it to be as efficient as possible... I mean, if I had come on here asking how to get 30mpg's out my 8000lb. truck, I could expect some critism... But anyways, this is turning out to be a pretty useful thread, I'm just going to sit back and soak up the information for now. I need to fix the leak before I start to think about spending money on upgrades.

I pull 27 if I do 55mph for the entire tank unloaded, so even 30 is doable with some mods I would say. But 14 almost sounds like something is wrong. I know everyone is telling you how to get better mileage but 14 seems so low that it can't just be a lead foot doing it. I mean most of us get that with a trailer in tow like others have already mentioned. What are your boost numbers and other vitals at a given speed?

  dorkweed said:

Do you have "gauges" in your truck??? If so, what were the reading prior to slowing and after???

I drive by the boost gauge and the EGT gauge; and I try to keep them as low as possible. Without lugging the engine of course.

Since this is a 2nd gen forum........do you have 3.55 gears in the rears??? What were you towing?? Was it big??? If so, you may have been out of the "sweet spot" of your truck. That's why I asked about gauges. They tell you so much about your right foot!!!

Aww common dorkweed - you should know i have more guages than most by now

3.53 gears towing a 8000lb 5th wheel. Same day, same road, about 4 hours later - next fillup - dropped it around 10mph, towing in OD. We were moving to FL.

Basically at 65-70 where I normally tow I get exactly 250 miles out of my tank when it reads 1/2 full. When I fill up its just below half on my fuel guage and hand calc results in ~12 mpg if its easy pulling, 11 mpg if its hard.

Since I95S was SOOO flat and for many many hundreds of miles I decided to try the slower speed test. The overhead was suggesting I picked up + ~0.75mpg ..... but actual calculation was 4 miles shorter than than previous fillup at higher speed.

So as far as I know - no tailwind (It wasnt windy anyway), as consistent conditions as possible. Right now I can only attest the following

* There's a certain amount of fuel/power required to tow 8000lbs - and that prevents large net increases regardless of speed.

* Like others have mentioned about the sweet spot for truck. Dropping 10mph might be slightly less efficient.

I'll have to try it without towing ...... but generally that gets harder due to variations in driving and traffic and stops etc. I totalluy understand Mikes theory and it logically makes sense to me - I just havent seen anything make substantial difference in net MPG apart from timing chip. Speed seems to have less effect for my truck.

Now I dont know what would have happened if I had increased 10mpg - eg 68-78 ...... maybe then it would have been terrible. I do know that if I run 55 without OD ...... so my rpms go from say 1400 to 2100 then I get bad mileage.

- - - Updated - - -

  ISX said:

I pull 27 if I do 55mph for the entire tank unloaded, so even 30 is doable with some mods I would say. But 14 almost sounds like something is wrong. I know everyone is telling you how to get better mileage but 14 seems so low that it can't just be a lead foot doing it. I mean most of us get that with a trailer in tow like others have already mentioned. What are your boost numbers and other vitals at a given speed?

Your trucks different Ryan. I think its the weight, low profile and tires and the mechanical injection.

Plenty of 12 valves pulling close to 25-27 mpg.

Very rare in a 24v. Generally 18-22 mpg.

My current billboard front camper tows much harder than my gooseneck horse trailer... much of it is windage but also the hitch load makes a big difference to the truck. To the point where I'm considering adding ballast to the trailer rear.

  flagmanruss said:

My current billboard front camper tows much harder than my gooseneck horse trailer... much of it is windage but also the hitch load makes a big difference to the truck. To the point where I'm considering adding balast to the trailer rear.

(Not to ) Don't you have a WD hitch? http://www.eaz-lift.com/eazlift/pro/pro_elite.html

  JOHNFAK said:

Your trucks different Ryan. I think its the weight, low profile and tires and the mechanical injection. Plenty of 12 valves pulling close to 25-27 mpg. Very rare in a 24v. Generally 18-22 mpg.

So are we to just say the 24V is just incapable of that kinda mileage and dismiss all attempts to try and get it there? I think not! guesswho512 had the exact same truck as me and could hardly get to 20, I think thats BS. There is something we are missing. I figured out the summer/winter variation issue (IAT difference) but now what is the issue thats keeping the vasssst majority of 24V'ers at 20mpg.. I'm gonna spend thousands on engineering/aerodynamic university that starts in a few weeks to figure out all these damn questions I have. I will not let complexity stand in my way, I will turn it into simplicity! I will not fail! Failure is for politics I will get these damn things to 30mpg, every one of them!

Yes, have the WD hitch it came with. I think I am exceeding the capabilities of the WD hitch. 2/3 of trailer is ahead of axles. All of living quaters is forward... rear of trailer box is essencially empty.

Do you suppose I could sell a 6 pounder (cannon) as necessary weight? Not mine, problem would be solved!

My swivels (swivel canons) aren't heavy enough.

On the return trip, with water tanks empty & black holding tank full (was able to irrigate with grey water) was very hard work to stay in lane (well mostly in lane).

I've also thought about converting it to a skeleton gooseneck.

MODERATORS: Feel Free to split into separate threads.

  JOHNFAK said:

Aww common dorkweed - you should know i have more guages than most by now

3.53 gears towing a 8000lb 5th wheel. Same day, same road, about 4 hours later - next fillup - dropped it around 10mph, towing in OD. We were moving to FL.

Basically at 65-70 where I normally tow I get exactly 250 miles out of my tank when it reads 1/2 full. When I fill up its just below half on my fuel guage and hand calc results in ~12 mpg if its easy pulling, 11 mpg if its hard.

Since I95S was SOOO flat and for many many hundreds of miles I decided to try the slower speed test. The overhead was suggesting I picked up + ~0.75mpg ..... but actual calculation was 4 miles shorter than than previous fillup at higher speed.

So as far as I know - no tailwind (It wasnt windy anyway), as consistent conditions as possible. Right now I can only attest the following

* There's a certain amount of fuel/power required to tow 8000lbs - and that prevents large net increases regardless of speed.

* Like others have mentioned about the sweet spot for truck. Dropping 10mph might be slightly less efficient.

I'll have to try it without towing ...... but generally that gets harder due to variations in driving and traffic and stops etc. I totalluy understand Mikes theory and it logically makes sense to me - I just havent seen anything make substantial difference in net MPG apart from timing chip. Speed seems to have less effect for my truck.

Now I dont know what would have happened if I had increased 10mpg - eg 68-78 ...... maybe then it would have been terrible. I do know that if I run 55 without OD ...... so my rpms go from say 1400 to 2100 then I get bad mileage.

- - - Updated - - -

Your trucks different Ryan. I think its the weight, low profile and tires and the mechanical injection.

Plenty of 12 valves pulling close to 25-27 mpg.

Very rare in a 24v. Generally 18-22 mpg.

Twas just checking!!!

When you slowed down, were your EGT's higher?? My truck actually runs cooler EGT's at 65-68mph empty, towing and running the air empty/towing than doing all the same at 55mph.

That's what I meant about out of the sweet spot. I've driven I-95 several times...........it is pancake flat mostly, but how was the wind in your travels??

AH64ID has posted that he'll often get better mileage at higher rpm's in 5th gear vs. lower rpm in 6th gear because he's not lugging the Cummins, and she's getting air to boot to keep EGT's down!!!

  dorkweed said:

AH64ID has posted that he'll often get better mileage at higher rpm's in 5th gear vs. lower rpm in 6th gear because he's not lugging the Cummins, and she's getting air to boot to keep EGT's down!!!

Exactly what I have noticed. Mine is geared to run 2100RPM at 70mph so thats what I aim for. Seems just as well at 65 but it's so high in the RPM at 70 that it has no turbo lag issues or EGT issues, 900-1000F the entire time.

  ISX said:

I pull 27 if I do 55mph for the entire tank unloaded, so even 30 is doable with some mods I would say. But 14 almost sounds like something is wrong. I know everyone is telling you how to get better mileage but 14 seems so low that it can't just be a lead foot doing it. I mean most of us get that with a trailer in tow like others have already mentioned. What are your boost numbers and other vitals at a given speed?

The only known issue at this point is the fuel leak somewhere behind the head. I actually turned my Edge down to level 1 until I fix it, because it doesn't leak nearly as much as level 5 does. But aside from that, my EGT's seem to stay in check with what they should be from what I've read, fuel pressure is always a solid 14-15psi, only thing I don't monitor too well while driving is the boost. But it seems to stay below 10psi under moderate acceleration, under heavy acceleration I've seen it in the 20's before.

- - - Updated - - -

  Mopar1973Man said:

(Not to )

Don't you have a WD hitch?

http://www.eaz-lift.com/eazlift/pro/pro_elite.html

Don't worry about hi-jacking, I don't mind the thread being used to help others as well, I'm just trying gain as much info as possible from peoples experiences.

  ISX said:

So are we to just say the 24V is just incapable of that kinda mileage and dismiss all attempts to try and get it there? I think not! guesswho512 had the exact same truck as me and could hardly get to 20, I think thats BS. There is something we are missing. I figured out the summer/winter variation issue (IAT difference) but now what is the issue thats keeping the vasssst majority of 24V'ers at 20mpg.. I'm gonna spend thousands on engineering/aerodynamic university that starts in a few weeks to figure out all these damn questions I have. I will not let complexity stand in my way, I will turn it into simplicity! I will not fail! Failure is for politics I will get these damn things to 30mpg, every one of them!

Love it Go get some !!! I'll be your test case If anyone can you probably can

  ISX said:

So are we to just say the 24V is just incapable of that kinda mileage and dismiss all attempts to try and get it there? I think not! guesswho512 had the exact same truck as me and could hardly get to 20, I think thats BS. There is something we are missing. I figured out the summer/winter variation issue (IAT difference) but now what is the issue thats keeping the vasssst majority of 24V'ers at 20mpg.. I'm gonna spend thousands on engineering/aerodynamic university that starts in a few weeks to figure out all these damn questions I have. I will not let complexity stand in my way, I will turn it into simplicity! I will not fail! Failure is for politics I will get these damn things to 30mpg, every one of them!

I wanna be on your team! Even with the lightest of pedals, Ive only been able to crack low 20s. Id love to be able to get into the realm of the 12 valves as far as mileage goes. Ive been looking into your guys IAT foolers and am interested in getting one together before the weather turns. I had a 2000 before my '98 and have always seen the drastic change in mileage from warm weather to cold but was never smart enough to understand why. This site has opened my eyes in alot of aspects with our 2nd gen rigs!

The IAT fooler is easy, buy the harness. I ran 3 wires to the knee panel & a toggle switch. I find it's worth 1 mpg in cold weather. It can be left stock to start & then switched to the fooler.

  diesel4life said:

I wanna be on your team! Even with the lightest of pedals, Ive only been able to crack low 20s. Id love to be able to get into the realm of the 12 valves as far as mileage goes. Ive been looking into your guys IAT foolers and am interested in getting one together before the weather turns. I had a 2000 before my '98 and have always seen the drastic change in mileage from warm weather to cold but was never smart enough to understand why. This site has opened my eyes in alot of aspects with our 2nd gen rigs!

That's the weird thing, I beat the crap out of it and can't get BELOW 21.. So why the 24V has to be driven like a smart car to get that is just ridiculous. I don't know what does it but it can't be that hard to fix. I mean the 12V and 24V operate the same way, they put fuel in the cylinder and make it go boom... since the 24V is completely variable, there is no reason it cannot match the 12V settings. Someone just needs to tap into it, but I think there has to be an easier way. Maybe the turbo boost needs fooled, maybe the fuel pressure needs fooled....who knows. I have the connectors and even the resistors you need to make this IAT fooler setup.. Think I even have a relay.

ISX... Unfortunately the 12V & 24V are two different critters. I'm sure the VP44, for all of it's adjustability, has smog setting built into the circuit boards. We can tweak them with chips & programers... but it would take a really smart dude to build a new board with pre-smog parameters. IMHO, the problem with smog controls is that it ignores effiency. The criterion should be least polution per mile worked... but we all know this.

  flagmanruss said:

ISX... Unfortunately the 12V & 24V are two different critters. I'm sure the VP44, for all of it's adjustability, has smog setting built into the circuit boards. We can tweak them with chips & programers... but it would take a really smart dude to build a new board with pre-smog parameters. IMHO, the problem with smog controls is that it ignores effiency. The criterion should be least polution per mile worked... but we all know this.

Lets say you are idling, but moving at 70mph, would you not be getting incredible mileage? Lets say you had an unloaded truck vs. pulling a trailer, is there not a significant difference? They aren't incapable of using less fuel.. The ECM on these things can only control so much.. There are much more efficient things out there, and things that haven't even been invented. All of which can make the truck require less fuel my making the engine more efficient or other means. Stodg has got the same mileage as me using propane, so it's not like the thing is incapable of being more efficient given the means to do so. But of course propane is an additional cost of course. I'm just saying that you have to think outside the box. The RV275 injectors gain you MPG's, higher fuel pressure gain you MPG's...what else is there? Could be several things we could be doing. Nobody would care if there wasnt an identical truck like the 12V's out there saying that yes you SHOULD be getting much better mileage. What gets me is the fact that my timing is static, I have 2 less valves, so the efficiency (theoretical) loss should mean that I get less mpg's than a 24v. But the 24V has emissions but do you really mean to tell me, that a truck, with more valves for better flow and variable timing, can not only be seemingly less efficient than a 12V, but also go beyond that another couple mpgs, just because of emissions?.... I keep thinking that the emissions loss would be gained by the efficiency improvement. I know compression ratio has something to do with it because a 12V is 17 or so and a 24V is around 16 ( You see all kinds of numbers on the net so who knows what it actually is). That has something to do with it obviously but it's still missing something. Plus the ppumper 24V trucks get the same mileage as they did with the VP as far as I have read, so it's not exactly the emissions doing it. We can go over this for hours, like millions of others have since 1998... Nobody seems to do much other than ponder about it. I'm gonna get to the bottom of it. I know there is a bit of politics involved and stuff that is keeping them from getting 30+ mpg, but even so I want to weed that crap out and figure out whats holding it back.

  ISX said:

That's the weird thing, I beat the crap out of it and can't get BELOW 21.. So why the 24V has to be driven like a smart car to get that is just ridiculous. I don't know what does it but it can't be that hard to fix. I mean the 12V and 24V operate the same way, they put fuel in the cylinder and make it go boom... since the 24V is completely variable, there is no reason it cannot match the 12V settings. Someone just needs to tap into it, but I think there has to be an easier way. Maybe the turbo boost needs fooled, maybe the fuel pressure needs fooled....who knows. I have the connectors and even the resistors you need to make this IAT fooler setup.. Think I even have a relay.

I sure hope you are correct. I'm glad you are doing something about this, I don't have the brains or know-how to get too involved in things like that... wish I did, but I just don't. Be sure to keep everyone updated as you uncover things. Anyways here is a short update: Been lighter on the throttle lately and shifting sooner (typically not more than 1700-1800rpm unless I need to speed up for safety reasons) I had been shifting probably around 2000-2200 on my last tank most of the time. The overhead is slowly going up, it may break 17mpg's for the first time since I owned it. If the ratio of increase is similar, should be putting my actual mileage up closer to 15 right now. I almost want to wait until my next fill-up to get around to fixing the leak, just so I can see exactly how my right foot alone affected my mileage...

I'm sure someone must have compared the 12V vs 24V cams, flow & timing... enlighten me. The 24V was built from the ground up as a smogged engine. By defination almost, a less efficient engine.