Engine/Transmission (1998.5 - 2002) 7 Mpg ???

[R-N-R]

7 Mpg ??? HELP!

Last weekend I towed my 28' Sunline of about 7100# with my '02 2500 QC, LB, 2WD (280 miles) and the OH indicated that I was getting about 7mpg (9 on the way home without firewood). The average was about 12mpg. Without a load I average around 17mpg.



I have the 4:10, in OD @ 65mph I ran 2200 rpm. In 3rd @ 65mph, I pushed 3000 rpm. It did not seem to want to switch back and forth so as opposed to what I have always been told, I ran in OD anyway. Hopefully this does not damage the trans, I traded in a 1500 gasser to get away from listening to the engine scream (4500 rpm) running 50 mph uphill.



I have been browsing TDR for two days now (what a wealth of information) and have not run across anything like what I experienced. Although I think that I was at the top end of my last truck, I have to believe that I am at the bottom end of capacity with this one.



This does not seem right!

Any suggestions will really be appreciated... ... .

 

[Mundgyver]

I gather you are running an automatic for the transmission. You might want to consider looking at an upgrade kit for the transmission in the way of a TQ converter and adjustments to the shifting mechanics and holding cirucits within the transmission. 7 mpg does not sound right. Slippage within the transmission could be your problem. I drive a 6 speed HO 4x4 quad short bed and have towed 9,000 and gotten 17. 5. There are others who drive the automatics that get this same range. Hopefully they will chime in with their knowledge as mine is somewhat limited in this area. Good luck

 

[R-N-R]

Mundgyver, thanks for the fast reply! I do have the auto trans. I have read that the OH redouts are not very accurate. I did not take an actual calc but I used fuel like I was getting terrible mileage. Thanks again for the confirmation, until I started reading TDR, I though I was going nuts... or made a big mistake trading in the gasser (5mpg).

 

[RPurdy]

My ride is similar to yours, except for the year and differential gear ratio (see signature) I'm pulling about 11,000 lbs and am getting 11 to 12 mpg (calculated). The overhead readout shows about 1 mpg higher. Something has to be wronge to drop your mpg to 7. I would have the truck checked out. I dont think that TC slippage accounts for this kind of mileage, unless you are really getting carried away with being the first out of the blocks at the lights.



Dick

 

[R-N-R]

Well, I am really enjoying being able to pull away from lights without leaving the next car behind me to deal with the pink (unlike my last gasser) hehehe



But really the 7-9 mpg was on the freeway with cruise control turned on. Using 3rd resulted in the mpg dropping to around 4-5.

 

[Mundgyver]

With cruise engaged, does the truck surge up and down in speed and if so, how much???

 

[R-N-R]

Does not surge at all, holds the speed very steady, drops a couple of mph going up a slight hill (lower Michigan) then returns to it's setting. It did not increase over the set speed at all. I was thinking that if the trans was slipping I would feel it or at least see it on the tach? I was watching the tach very close to see if it was shifting on me. I slowed to 55 and dropped it into third just to make sure that I was not downshifted without realizing it. And the RPMs did increase about 8k (seems like a lot between OD and third). Is 3000 rpm @ 65 mph in 3rd normal with the 4:10?

 

[Mundgyver]

4:10 rear end will cause higher RPM. As far as the correct tach for your speed, I can't answer that one as mine is a stick. I do know that if you use a needle valve in your vacuum circuit to the cruise control and set it to almost closed, your throttle response while in cruise will be alot slower and you should be able to hold within 1/2 mph of selected speed. For me, this one mod gave me about 2/3 of an mile per gallon better fuel economy when using cruise. The other automatic guys should be able to tell you if your rpm is right.

 

[Steve Campbell]

3000 rpm is....

way out of the efficiency curve for the Cummins. Obviously your speed would drop, but 2200-2400 rpm would be a more efficient loaded pulling rpm.

 

[illflem]

A couple of things. How many miles on the truck? Your mpgs will increase after it's broken in, about 15k. I've also found that using my foot rather than the cruise will increase the mpgs by 2 or more. The cruise just reacts too much and is constantly adjusting, diesels perform better with a constant throttle.

 

[98rammer]

pulling my dad's snowmobile trailer (around 2000 lbs) i get only around 12. the stock torque converter is very wasteful of energy (turning it into heat) and with the basically stock motor i'm floored 1/2 of the time with that trailer. it's all dependant on the ground level, your motor, transmission, aerodynamics, and basically the way everything is running in general.

 

[LarryB]

Re: 7 Mpg ??? HELP!

Originally posted by wesoule

I was getting about 7mpg (9 on the way home without firewood). The average was about 12mpg.

How do you get 7 and 9, then average 12? I think the first thing you need to do is a little more acurate mileage check. 12 pulling/18 empty is about right with a stock auto and 4:10s. Slow down to 60 and you'll do better. Revs and a lead foot make a huge difference.



What mileage did your gas pot get pulling this same load? Or could it?

 

[CUMINNTSTRKN]

with that light of load you should get around 12mpg. when we towed my truck to muncie we avg 7mpg for 3600miles. but we were going 80mph and our gcvw was around 24k.



jim

 

[cwarner]

I just towed 10500#'s back from Torch lake Sunday and got 11 on the OH and that was towing around 75-80mph with the AC on.



The truck seems to like 2000-2100rpms the best, that is in OD with 295 tires and 3:54 gears.





With my boat on (7000#'s ) I have seen 13mpg on the OH.



A funny thing is I let my girlfriend drive on the way up (no trailer) and she used as much gas as I did pulling the trailer on the way home ! I woke up at one point and looked at the speedo and saw it between 90-95 !!! I just went back to sleep:--)

 

[Koa Man]

I average 10 mpg with my truck. 5 ft. high flatbed headboard is a killer on mileage, as well as running around at a GCVW of 12-16K most of the time.

 

[R-N-R]

LarryB, I was reading the overhead trip computer for the current (7-9) and the avg (12) which included driving empty and getting upwards of 18mpg. I know the trip comp. is not very accurrate but I used almost a 1/2 tank of fuel on a 130 mile trip so I estimate that the 7 was close. I got 9 on the way home w/o the firewood. I watched the speedo & tach very closely and in OD I only ran 2200 rpm. My old gasser pulled the same load @ 4. 5 - 6 (downhill with a wind) and did not take too kindly to going up hill.



12mpg would not have surprised me although I was hoping for at least 15 with the light load (7100# TT). 10 would not even have shaken me with the truck being so new. 7 scares me!

 

[R-N-R]

After reading TDR posts for the last two days, I realize that this problem sounds outlandish, stupid, or just plain old full of crap. But the rpms, speeds, gears, etc. that I've reported are accurrate. I am sure that the truck has a problem but I hate the idea of walking into the dealer without any ammo (info). Being new here, I really appreciate the responses and remain hopeful that the CTD veterans can get me pointed in the right direction.

 

[LDusky]

I don't know if you have guages, if you do look at your EGT,s and boost. If your turbo hose has pooched open your egts go up and your boost goes down and so does MPG.

 

[Wolfgang]

My first pull with my truck and a 9000# 5th wheel I averaged 10 mpg. On the last pull on the flat I made with my mods (see sig) I averaged 12. I have 3. 55 gears. 7 mpg does seem a little low. I suggest you do a mileage check. Take a flat surface of 50 or 100 miles or so make a run with the trailer and see what you get. Hills (even small ones) and or wind will change your mileage significantly. I think if you get between 10 and 12 in this circumstance you are probably not doing to bad, if not take it in.

 

[R-N-R]

Don't have gauges... yet

Is a pooched open turbo hose something I can visually inspect?

Also, the truck seems to be in the "normal" mpg range w/o the load. Is it possible for the turbo hose to develop a problem while pulling a load?

(sorry, I'm working on the newbie thing)



Wolfgang, I'll definately run a test as you described with a more accurate method of collecting the data!



Thank You!