SCR wrote: On my 06 3500 DMAX/Alley I leave it in drive and use the TH until it starts searching for gears, up and down shifting, then I use the Manual to hold it in the the lower gear till the road evens out.
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That sounds like a good plan. On my short trip of about 600 miles, I pretty much left it in TH. However, the terrain in which I was towing was full of hills and twists and turns - perfect for riding a motorcycle, but not for towing a FW! I found that I pushed it out of TH pretty often as it wanted to stay in a lower gear in conditions where I thought I'd be okay in a higher gear. So in those places I pushed the TH button to knock it out of TH. However, after reading your post I think I might try your technique.
I'm curious about my mileage but I don't plan on watching it too closely for another 5k or so. I averaged a little over 11 on the 600 mile trip, however about 80 miles of that was with the FW disconnected. I was expecting a lot worse under those conditions. My previous 2004 DMax got 11.4 mpg over about 6000 miles with this FW, but only about 2 trips were in the Ozarks, the rest was Memphis to Florida where my mileage ought to have been better.
Traveler II wrote: We just got back from a 6,500 mile trip with our new Duramax. When we were towing we had it in tow mode and just left it there. The Allison was a wonder, it held the speed both going up and coming down, even the long grade coming into Denver. Because of the cost of diesel we drove 55-60 and got 11.3 towing. Our rig comes in at about 11,500 pounds and I think the mileage will get better with time.
You are right for the manual, as of yet I've not found a need to use it, I just let the Allison in tow mode do it's thing.
One question I have is; when do you change the oil? Do you use the % indicator or change at 5,000 miles. This time I waited until I got home and it had the 6,500, but the indicator said I was at 45%.
Thanks for that feedback. You are now towing at the speed where I did with my previous 2004 DMax, and I got 11.4 mpg, however my FW weighs a little less that yours. So you are doing something right! Heck, there are just you and me running at that "slow" speed, so we can wave at each other when we pass each other some day!
On the past trip, the first 600 towing with the new truck, I found I went in and out of TH mode. I thought the Allison was staying in a lower gear more than was needed. But then again if I'm on a less winding and hilly road the TH might do well. My previous DMax, the 2004 with an Allison but without the current 6 gear, did not stay in high rpms/lower gear as much as the 2008 did last weekend on this same route. Not sure why, but I suspect the gearing differences were at work, and I'd be fine, MPG-wise, even leaving it in TH. But it bugged me, so I flipped it in and out of TH!
On the oil change issue, you will get my opinion, which is worth what you are paying me; nothing! I used to change the engine oil and filter, plus the Allison external spin on filter about every 4-5k, although I also checked the "Oil Life" on the DIC, which was usually about 40-60% before I reset it. I believe with the new truck and higher oil prices, however, I will wait until the Oil Life indicates a little higher; like maybe 70% before I change the oil and filters. However, my truck is used 95% for towing, so it sits around a bit in the winter. So I try to do a change before it goes into storage. I say storage, but even in the Nov-March period where it doesn't tow I still get 200 miles or so a month. I don't think it's good to get zero miles on it for 2-3 months.
You will also get different opinions on what oil to use. I use Shell Rotella. I use the non-synthetic in my truck and the synthetic in my motorcycles. I've been using those two for several trucks and motorcycles, and found no reason to change.
Wingnusa wrote: I run in TH mode all the time except for heading into or going down a steep grade. I don't feel the Ally shifts down quick enough heading into a grade so I shift to manual and shift down before I start the climb. Seems to work much better. I get between 11.5 and 13 mpg with our 16k lb 5er with 41k miles on it. Oil change...only when it says to. Most diesel mechanics will tell you that you're throwing your money away if you change it like your Grandpa's diesel. Mine goes between 8-10k miles between changes. More important on the changes is your fuel filter....
Thanks for that, Scott, especially this part "More important on the changes is your fuel filter....".
I replaced my previous 2004 DMax at 44k miles because my "Water in Fuel" DIC message was never displayed and it should have. I was ignorant of fuel filters until my truck started running odd - bucking around, noisy and wouldn't run above 2000 rpm. I took it to a Chevy Dealer in Florida who said my filter was clogged. He changed the filter and told me to "run it hard". About 100 miles later I was getting towed.......30 days later I paid a $6500 bill to another Chevy dealer.
Bottom line: If anyone reads this who is as woefully ignorant as I was, change your fuel filter about every 12k. You have to do that yourself, or watch someone else do it, as Chevy does NOT cover damage to your truck due to water in the fuel system. I no longer consider that my truck is warranted for anything to be honest about it. I did trade that 2004 Chevy after paying that $6500, which luckily was covered my my truck insurance - Three cheers for USAA insurance! Anyway, I traded because the previous DMax sounded a little off, and felt a little off, after the Florida dealer replaced most of the fuel system. I was never comfortable that "Mr Goodwrench" knew his elbow from his you-know-what. A new fuel filter obviously will not save an engine with 2 gallons of water in the fuel tank like I had, but it will alert you to the fact you OUGHT to get a warning on your DIC, and you probably will NOT get that warning - being knowledgeable about the filter, etc may help you avoid a costly repair bill.
By the way, even though I admit my ignorance, when the truck first started sounding and running oddly I immediately called Chevy Customer Service, who simply told me to take it to a Chevy dealer soon. I even asked if I should have it towed; they connected me to a nearby dealer who said "Nah, drive it in - no problem". That is the same place that changed the filter, charged my about $100 and told me to "run it hard".
With only 750 miles on it the Allison might still be learning. Once you start towing it probably won't seem like its hanging in the lower gears quite as much.
Ah, I think you are correct. I noticed that on my previous DMax, but had forgotten.
Hamops wrote: ..I like the Allison's Grade Braking feature for short hills but for long grades, I just don't get warm and fuzzy feelings about the Dmax doing 4000+ rpm...
I don't either. I saw 3500 rpm or so on my last trip in TH mode. I didn't like that.
So in manual you just shift into, say (Manual) 4th going down a long grade and keep the speed under control with the occasional brake application? In Manual the trans will not down shift going down the grade, right? I know it will up shift only to the manual gear you have selected.
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