I expected to MPG's to go down, but....!

[JYaekel]

I am new to the community, as well as new to my 98. 5 4x4 auto diesel. I recently hooked up my utility trailer with pressure washing equipment on it and took it for about 150 miles to a job.

Well, I was rather shocked at the drop in the mpg's!!!

First off, my trailer with equipment only weighs about 2500 lbs (and I think I am being very generous with the weight). It does have a 4' Ramp gate on the back for loading... .

With no load on the truck, I am getting between 18 and 19 mpg doing between 65 and 70 mph. I figured for a 4x4 auto this was about right..... After towing with the trailer, however, I am getting about 10 - 11 mpg tops!!!. Being as this is a light trailer, I did not expect the truck to even notice the load much less show that much of a reduction in effieciency. Driving habits were kept the same between no load and loaded mpg test.

I am wondering if the tail gate (though it is of metal mesh) could be adding to the problem???



Any thoughts and advice from you pros would be greatly appreciated.

 

[Deezul1]

Towing a 6000lb TT I go from 21mpg to 13. 5mpg so you dropping to 10 seems really odd. I bet the aerodynamics of that trailer are terrible too. If this is something that you do a lot then try to make up some kind of wind deflector for the front of that trailer. Look at what the semi's put on the roof of the tractors just for this reason.

 

[Ron Bissett]

Air flow has got to be the cause or driving in over drive on hills could be a factor, possible drag or resistance to roll of trailer wheels . Hard to understand that loss of mpg with a total load of under 3000 lbs . Keep checking . Ron Bissett in Metro Louisville KY

 

[keimmmo]

Wind resistence can hurt you more than weight. I have an 16 ft cargo trailer with a lot of "barbs" down the sides. It hurts my economy way worse than my 35 foot travel trailer! I'll bet the wind resistence of your trailer is the problem.



Steve

 

[Mad Bomber]

MPG's

Check your boost clamps. There are 9 clamps for your intercooler they need to be kept at 95 inch LBS. NOT FOOT LBS. Eric

 

[Doc Tinker]

BOMB the truck, you'll be surprised that more power may give you an increase in mpg. I get a consistant 11-12 towing a 10,000# travel trailer, using a Bullydog box and 275 injectors (mild BOMB)



I have acheived 24 mpg while driving a consistant 65 mph, unloaded.



Doc



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2000 2500 5sp 3. 56

 

[soslow91]

I suspect the restrictive hy35-9cm turbo that I believe your truck has is at least partly to blame they make more boost than they need for the power they are making which increases drive pressure and egt lowering economy.



My 91 with an h1c and an 18cm exhaust housing gets 15-16 towing almost 10k with an automatic and no lockup.



A free flowing exhaust system would help as would switching to an hx35 with a bigger exhaust housing most people who tow use the non wg16cm you will have a little more lag with that turbo but you can do other things about that (more fuel and more smoke)anyway hope this helps

 

[Steve Campbell]

That ...."tail gate (though it is of metal mesh)".....

Is a real killer. It is not aerodynamic at all. Putting plywood over the mesh would make it pull easier. Could you "hinge" it in the middle so it is only 1/2 as tall? That would cut down on the drag considerably.

 

[DDT]

I am wondering if the tail gate (though it is of metal mesh) could be adding to the problem???

AS said -Wind resistence can hurt you more than weight

If you can do a test if possible.

remove the tail gate for one trip, you will see a big difference. plywood would be less wind drag.

Have you ever noticed the truckers hauling plastic pipe. if you trap the front it pulls alot easyer.

 

[wcjp]

My commute is all freeway. I drove one complete tank going the same route everyday with no tailgate. No difference at all. What's the tire pressure on the trailer? Have the bearings been greased lately?

 

[DPelletier]

wcjp, I believe they are refering to the ramp gate on the trailer, not the truck tailgate. Is that what you were talking about when you said you removed your tailgate?

Dave

 

[scbroder]

Just wanted to jump in on the tailgate conversation. There have been extensive tests on air flow around a truck in an effort to improve fuel economy. These tests conclude that the air above the bed and around the tail gate is extremely turbulent. As a result, it is my understanding that in terms of resistance, it does not matter what type or if you have a tailgate or not.

However these test would have been conducted without a trailer of any type, I suspect this would have very little effects on the outcome of the tests.

 

[Dean Upson]

Originally posted by scbroder

There have been extensive tests on air flow around a truck in an effort to improve fuel economy.

Check out http://mars.wnec.edu/~ehaffner/did.htm





Dean

 

[scbroder]

Dean, great site.



I believe the study I was referring to was a Ford Ranger, I just assumed this would apply to all pickups in general. I wonder if my previous post holds true for Rangers? Apparently it doesn't for our Rams.



What surprised me the most was the drag coefficient increases by approximately 7. 5% when the tailgate is removed, versus a lowered tailgate. It just doesn't seem intuitive to me that there would be much difference.



Anyway, thanks for the info.

 

[JYaekel]

Thanks for all the advice so far - really appreciate it! I thought I would give an update since the initial post:

My truck also had a problem with "hunting" when it went into overdrive, so I did a recal. on the Throttle Pos. Sensor, and it has been fine ever since. As a result, my mpg's did go up a little.

My best has been no load on the highway giving me 18. 5 mpg.

Loaded with the trailer gave me about 15. 5. However, my last trip with the trailer (about 150 miles mostly highway, but some city) gave me only about 14. 5mpg. I am not sure why I am not getting more consistant results, but I am happier than the mpg's I was getting before the recalibration.



I am also running all-terrain wheels (315/75/16). These came on the truck when I purchased it, and they are almost new, so I figured I would run them. I think they are about a 32 inch diameter (approximately). I am thinking this could be part of the problem as well. The tall tires are giving me low rpm's. Around 65 mph, I am doing about 13 or 1400, I think..... (adding in the error for the tire difference). I am wondering if I had stock tires on the truck (265's, I think), if my mileage would be any better? I figure perhaps the increased rpm's would might put it in a more efficient range for optimal mpg's... .



Any thoughts???????

 

[wcjp]

I think for an auto with oversized tires your mpg is about right.



I was talking about the tailgate attached to the bed of the truck as provided by DC. It made no difference with the tailgate on or completely off the truck. My 81' Mazda 4cyl I had in highschool this did make a difference.

 

[Murietaman]

Im getting 16 towing a 29 Alpenlite, (10,300 empty). That included twice over Pacheco Pass by Gilroy CA. BD exhaust worked great keeping me at 55 on both sides of the hill. Also have Power Edge EZ. 99 2500 4:10. Oo.