hotshot guys- real mileage gains by slowing down???

[Rockcrawler]

I ask this of the hotshot guys but really welcome input from anybody who hauls a lot at 20k + wt and miles annually.



My main tow rig is an FL70 toterhome with Cat 3126/edge box and fuller 6 speed. 3. 90 gears, 22. 5 michelins, 2000 rpm is right at 76 mph. Peak torque is 1400 or so. My race trailer (enclosed 28' GN) fully drafts the toter and has a roundish nose and top. we are about 27k total going down the road with 10k of trailer/gear.



we put on about 25k miles annually. traveling a good part of the country. we see a lot of west driving and 70-75 speedlimits, typically we drive 7-8 over the limit which the truck does fine, pulling down a bit on hills but almost always carrying 6th to the top.



Sometimes, we are not crunched for time, and we could slow down to say 65-70 for 1400 miles one way or maybe even the round trip. So if I sacrifice those few hours, what are the real world gains to be had on fuel burn? We have twin 45 gallon tanks and the few times I drive that slow it's not long enough to get an accurate read.



We seem to get 7. 5 average no matter what doing what we have been doing. When I towed in a similar way with my Dodge I was getting 8. 5 to 9, but the crew is a lot more happy traveling in the toter and I skip the hotels when i get there to offset.



Anybody have a good educated prediction?

 

[R C Cola]

Mpg

Every rig is differant. Almost free miliage to be had by freeing up the intake and exhaust. Then run tires at maximum shown on sidewall for inflation. Then go to a good CAT Dealer and find out where the sweet spot is for that specific engine. Then drive with the tach as close to that spot as possible. R C

 

[Rockcrawler]

Every rig is differant. Almost free miliage to be had by freeing up the intake and exhaust. Then run tires at maximum shown on sidewall for inflation. Then go to a good CAT Dealer and find out where the sweet spot is for that specific engine. Then drive with the tach as close to that spot as possible. R C

Tire pressure is a given, I'm not sure I see the intake and exhaust opportunity on a turbodiesel, they each flow well and I can't recall this as a kink in the proverbial hose. I've got a huge AFE element for the intake side and not sure you can improve on the stock intake more than that (feasibly) and the stock ex is 4" into 5" into a huge 5" muffler- again not much more to do. 1440 is peak torque and they don't advise downshifting til a few hundred below that. I can't drop that low in RPM without regearing as I'm not yet retired and I need to get where I'm going within reason.



I did check with a bud who owns/runs a trucking co- he seemed to think about 1 mpg per 10 mph to be had- I'll try this trip at 65 or so and see what happens- 1750 RPM

 

[JHardwick]

I run all 48 states and document every fill up. I can see as much as a 4mpg swing if I'm heading west through some mountain passes with a strong head wind at 70-75mph or I'm heading east over some relatively flat terrain with a little tailwind on state roads at 55-60mph. Those are extremes, but I'm guessing a 2mpg increase from 75mph to 60mph on the same stretch of road.

 

[johncameron]

I tested the difference between 55MPH and 68MPH last summer pulling my 6000# enclosed trailer. At 55 MPH I got 13. 5MPG. At 68MPH I got 10. 7MPG. It was the same day with the exact same conditions except for the speed of course.



So I guess speed DOES kill!



John

 

[bmoeller]

The intake isn't that big of an issue with those engines. There may be a better muffler, however. Some mufflers have baffles, some don't. If it has baffles, look for one that doesn't. It will help reduce backpressure, and may or may not gain a tad in mpg. Will lower EGTs a bit, as well.



Is your engine set at 250hp or 300?

 

[Rockcrawler]

The intake isn't that big of an issue with those engines. There may be a better muffler, however. Some mufflers have baffles, some don't. If it has baffles, look for one that doesn't. It will help reduce backpressure, and may or may not gain a tad in mpg. Will lower EGTs a bit, as well.



Is your engine set at 250hp or 300?

250/800 with the Edge set on 4 for 40/120 increase. I've considered turning it up to 300/860 thru Cat but have not got around to it.

 

[Oasis-3]

1999 Fl-70

Rockcrawler

I ran my FL-70 3126 250 hp cat 7 speed trans 22. 5/195 full size truck tires for just over 2 years and close to 200,000 miles pulling a trailer that was 10K empty then add 4 cars total weight never went over 45K and always got 8 to 8. 5 mpg But in the winter it went as low as 7 mpg one or two times with winter blend fuel and running very hard.

I would try to run one way with the edge box off and see if your milage is any better.



Good luck

Cliff

 

[KBalzuweit]

You would find that if you run about 1550-1600 rpm you will get the best economy. Atleast that is what I found when I had my topkick with a cat.

 

[jelag]

My 04 dually pulls 20 to 22 K trailer all the time. . its stock... . manual transmission and 4:10 rear end..... its never seen a full tank of fuel empty (stock tank). . the truck now has 185K miles on the clock... . we see around 10. 5 on the west coast in OR and CA where we can't go over 55 - 60 because of the limits... . maybe 11 on a good day... . when we drive the return trip... . from Phoenix through NV, UT, ID, MT and back to Spokane we don't see a lot of difference at 75 MPH... . Maybe 10..... I don't think we've ever had a tank of fuel... . under 10 MPG... . that is... for us a tank of fuel is 120 gal..... We record all services including fuel costs.....



I don't think I'd drive I-5 through OR and CA faster than about 60 anyway... too much traffic and careless people behind the wheel... just can't get enough spacing to feel good..... from entering NV from CA on US 95 north up to Vegas and north on I-15 and west on I-90 we open it up... and don't drive much faster than 75-80... .



Hope this helps... .

 

[Eric_77]

Well I have a similar rig FL60 with 190 hp 3126 5 speed fuller (straight truck no trailer, 26k gross) Running 70 I am at around 2400 rpm motor is screaming and it has run that way for 340,000 miles. (life average is 8. 75mpg) Found the best mileage is actually a touch over max hp (ie 70mph)as I can maintain speed over hills but on pure flatland I see as much as a 2 mpg increase by running at 65 but any hill puts me down into 4th and 50 mph.

 

[y-knot]

I do not tow all that often, but I do know if I slow down from my normal speed of 75-80 mph to 65 mph, I pick-up an extra 165 miles per tank. I have been driving alot slower lately.

 

[Rockcrawler]

Well the results are in- 1st tank was already half burned at higher speeds, but ran 1800 rpm at 68 mph the remainder- 8. 5, next tank was 9. 0 with cruise at 68. From Gallup to flag and down to phx we used less than 1/2 tank and managed 10. 2?? (did not expect that with the hilss but maybe a tailwind and flag is 5000' uphill from phx. )



Phx to Santa rosa was 8. 8 then to Eastern Ok was 8. 2, the 8. 2 kinda surprised me as a low- maybe a head wind but the wind is usually out of the south. I'll keep running this way as long as time permits- worth some coin on a long trip



Thanks for all your help. One thing I noticed was that at 68 you still had quite a bit left if you had to get around someone, driving 83 or so there's not much left

 

[NVR FNSH]

Phx to Santa rosa

Santa Rosa, CA - north of SF? What were doing up here?



Brian

 

[Rockcrawler]

Santa Rosa, CA - north of SF? What were doing up here?



Brian

Santa Rosa, NM- I run route 40 a lot going to comps- headed to Cedar City UT, next week

 

[Oasis-3]

7 Speed

Time to look for a cheep 7 speed fuller = go faster with lower rpm's



Cliff

 

[Rockcrawler]

Time to look for a cheep 7 speed fuller = go faster with lower rpm's



Cliff

any more scoop? I'm seriously considering some type of gear change. Just looking at bang for the buck whether to look for an aux transmission, 3rd member change or a hi/lo axle. Won't bother me to downshift on bigger hills, would be nice to cruise 1600 in the flats and still have 70+ mph.



How wuch torque are they rated for? top and low ratios?

 

[Oasis-3]

I don't have #'s

I don't rember the numbers /ratios I let the books go with the truck when I sold it. The truck was a class 7 33,000 lbs. and combined weight of 52,000 lbs. I do rember I had to be going 70 mph and up to use 7th gear and 1st gear was so low that I only used it to pull out on a hill when I was loaded. Do a search on Fuller transmissions and you can fined a lot of info. If I would have had that truck much longer I was looking at putting a 9 speed in it so I would have more gears to help me up some of the big hills when it was loaded.



Good Luck

Cliff

 

[MMeier]

With my rig ( see sig) and running 2 cars to SoCal and a container on the return trip, I've been averaging 9-9. 5 MPG. However for a couple of days when it was really windy through the high desert, I saw that number as low as 6!! :{ . truck and trailer (empty come in at 18. 2k#), add 8500-9300 for a 40' container.