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Frank P. Martin 09-19-2009 08:02 AM

Driving In Tow/Haul Mode When Empty
Does anyone in tow/haul mode on a regular or even infrequent basis when empty? In my experience, so far, I can understand where for those driving in relatively flat areas, tow/haul wouldn't buy them anything.

However, I find that here in the hills of Pennsylvania, using tow/haul when empty seems to have advantages. I even invoke it momentarily when slowing down for red lights and on downhill grades for the additional engine braking that just isn't there when not in tow/haul mode. Uphill, the truck seems to pull easier and responds quicker when more power is needed; more like my 5 speed manual Ford PowerStroke did. Although it pulls OK uphill when not in tow/haul mode, to me, it feels like the engine is somewhat lugging and response is sluggish because it's always at a much lower RPM.

What I'm really interested in is fuel mileage. On the flats, yes, fuel mileage would most likely suffer running in tow/haul mode. But, I'd like to hear from those who drive in hilly areas as to what difference in fuel mileage, if any, they've noticed driving with tow/haul mode on vs. tow/haul mode off when empty. Your experiences, in general, would be appreciated too.

From what information I've read so far, it's OK to use tow/haul when empty but shifts may be more abrupt. I also suspect that you might be changing your oil a little more frequently as I believe the Oil Life percentage that displays on the DIC (for those who have this feature) is based on engine revolutions and, of course, there will be more engine revs when in tow/haul mode. Correct me if I am wrong about this or if there are other criteria in determining when the oil needs to be changed.

Hitchhiker 09-19-2009 08:30 AM

I use my tow/haul when empty frequently on grades. I'm in a mountainous area and using it lets the Allison downshift when needed on downgrades and keeps up-shifting to a minimum on the switchbacks on upgrades.

I haven't evaluated any differences in mileage using it, here in the mountains mileage is what it is. What you loose going up, hopefully you get it back going down.

Ray,IN 09-20-2009 08:44 PM

This" Frequently Asked Questions: Service: Allison Transmission
is all I have to offer to your questions. I use tow/haul in hilly areas when empty too, I don't notice any detectable drop in fuel mileage when empty. I suspect it's because the engine isn't working hard. I've even noticed that I get better mileage using tow/haul when towing in hilly or windy conditions, this again I attribute to the engine not working as hard as it does at lower RPM.

Frank P. Martin 09-21-2009 08:08 PM

Thanks for the link, Ray. I read through all the FAQs but some of them appear to apply to the older 5 speed transmission and I have a 6 speed. I also downloaded the "Getting To Know The Duramax Diesel" booklet. I received the booklet when I bought the truck but having a "machine readable" copy is great because I don't have to run out to the truck (where I keep it) for it whenever I need to reference something.

From what I read on the Allison website, it seems that other owners use tow/haul mode when empty for many of the same reasons that I do.

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