We've done about 2,000 miles in the last two weeks. Our trailer is a 28' CCD, loaded pretty light at the moment. Our TV is a 2001 Chevy 2500HD with the 8.1 gas engine and Allison transmission.
We've been getting around 11 mpg, generally at 55 mph. We did a couple of stints at 60 mph, and a few where we slowed a bit due to construction. No noticable mileage difference in either case. I suspect the increased aero drag from going faster might be offset by the engine breathing a bit more efficiently at the wider throttle opening.
At 55 mph in T/H, the Allison will not switch down to overdrive. Once we go a little over 60, it will. So I just take it out of T/H when I'm cruising in a flat area, which will cause a shift into overdrive, then immediately turn T/H back on. That gives me the brake assist if I ever need it, without forcing the engine up 600 rpm needlessly while cruising.
I think a lot of this discussion proves that different transmissions are programmed differently, and that gas engines benefit somewhat less from brake assist than diesels.
Our truck also seems pretty insensitive to weight and speed when it comes to mileage. The best I've ever done while not towing was 17, but I typically get 13 or so.
I might have rather had a diesel in the first place, but we got our truck used from my brother in law who lives in Wyoming. At his altitude, and with the wildly variable weather out there, diesels are sometimes a problem. When we get our next truck, it will probably be a diesel (GM stopped making gas/Allison trucks anyway).
I might have rather had a diesel in the first place, but we got our truck used from my brother in law who lives in Wyoming. At his altitude, and with the wildly variable weather out there, diesels are sometimes a problem. When we get our next truck, it will probably be a diesel (GM stopped making gas/Allison trucks anyway).
Hi Ag,
This is odd; typically normally aspirated (most gasoline powered truck engines on the market today) engines do poorly at higher elevation. Turbocharged (most diesel engines on the US market today) are not prone to performance loss at elevation.
Anyway, every time I am out towing with the Allison, I am just amazed at its performance. I have owned many trucks over the years (this is my first diesel) and regardless of what engine they have had, there is nothing like this Allison (that I have driven). I can’t imagine a better tool for towing. The rock solid shift patterns, engine braking, and reliability make me feel like I am driving a locomotive-towing is a pleasure with this combo; solid, stable, plenty of juice for hills, passing, etc. It is a good feeling to know when you hitch up and head out that you have such a platform to haul your family, and stuff!
You do have a point about different trannies and rear end ratios, and their effect on performance. When I am towing (62-63mph) I can pop it in/out of TH and the tach does not change at all (mpg constant also). This is a D/A with the standard 3.73:1 rear end and 6 spd Ally.
Bill
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We drive an F250 PSD and use the "Tow-Haul" mode whenever we tow (and don't forget to press the button). Probably would not be a bad idea for the pickup manufacturers to have an "idiot" light (what's one more light?) that recognizes that a trailer is attached and would ask you if you would like to utilize "Tow-Haul" mode at this time.
On my Avalanche the only thing tow/haul does it extend the shift times - I does not keep it out of overdrive. I also tow in 3rd rather than drive - my transmission place showed me the clutches in the transmission and after seeing how small the overdrive clutch is, I never tow in overdrive. Chevy says you can tow in o/d, but their warranty is only 36000 miles - if you keep the truck for the long haul, you will wear out the transmission
Ken J.
Same with my Safari. It just moves the shift points to allow for pulling a heavier load. In turn, this saves on the tranny.
This subject has been discussed many times here on the forum. Use the search function and you will see a ton of advice. But while I am here, We always have the Tow Mode engaged and Overdirve off when towing. It is in your truck for a reason and hence you should use it.
Rick
__________________ J. Rick Cipot Sandi Gould NEUNew England Unit Airstream Life Magazine WBCCI #3411 AIR #17099
Use the search function and you will see a ton of advice
Oh poppycock. The search function on this site is worthless, but someone here told me about using google's search engine to search the airforums.com site. The google search syntax is:
xxxx site:airforums.com
where xxx is what you are searching for.
There you will find tons of advice.
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We drive an F250 PSD and use the "Tow-Haul" mode whenever we tow (and don't forget to press the button). Probably would not be a bad idea for the pickup manufacturers to have an "idiot" light (what's one more light?) that recognizes that a trailer is attached and would ask you if you would like to utilize "Tow-Haul" mode at this time.
I agree because I often forget until we are under way and I don't think it is a good idea to press it while moving. It may not hurt it, but I think it best to be stopped, if not in park, when you engage the tow/haul mode.
I may have mentioned this already, but I wish the tow/haul reminder light were blue or green or some other color besides yellow. It makes me think something has gone wrong when I see it out of the corner of my eye. To me yellow and red are warning colors not reminder colors.
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Reading the glove box manual helped me understand when to use TH.
The GMC Denali has an autoride system that varies the shock absorber valving to suit road conditions. The TH mode recalibrates this system for firmer damping. Therefore, I use TH w/o the trailer when traveling tight mountain roads. Gives it damping more like the great Z-71 suspension system which is only available on the 5.3 Tahoe/Yukon and not the 6.0 Denali Yukon.
I have a 3/4 ton Burb too and use tow/haul when on the road towing all the time. I have yet to see and RPM increase due to tow haul on flat land at 55mph or faster. I do note that it shifts later and can hold the RPMs while in the lower gears, say 2nd, but after 40mph, it shifts to the next gear, then the final OD gear. What tow/haul does is keep the trans from overshifting when you come to smaller hills, etc. FWIW, I have 4.10s in the back.
mr winkie,
i'm surprised you find time to drag an airstream. i thought posting while driving was not encouraged or worse...
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