Duramax Owners

[t1mrtork]

Gary
Do you notice the tranny tempature going up when it is in overdrive?

[Bob Pasternak]

Terry; We have, as you can see by my profile, a 3/4 ton Dodge with the Cummins in it. It was set up with the tow/camper package. The camper package is heavy duty shocks and sway bars along with oversized tranny cooler and radiator. It also has a larger battery and alternator. I added a PMT power chip, 4" exhaust and Auto Meter gauges. The last trip we took the tranny temp never went over 180 degs in August running up in the northeast. And I run it in overdrive and cruise as much as possible. Take it out of OD in towns for the engine brake. Take the cruise off if I'm approaching a hill that I think might cause it to disengage. With my foot on the throttle, I can just about feel when it is ready to shift and ease off to keep it in the torque (1500RPM) range on my engine. 1800 RPM in OD gives me a little over 65 MPH and since we seldom run interstates, that's fast enough.

[NJ Hillbilly]

Terry, when T/H is engaged not only do the shift points change but the torque converter locks up in all gears. Once the converter is locked, the trans doesn't really generate much heat. It's the unlocked converter slipping(that's what it does) that generates 90% of the heat in the trans.

My temp stays steady but when there are some shifting going on it does rise. I changed my trans pan to a deeper one that holds about an extra gallon of fluid and I switched to the Allison synthetic trans fluid. The temps aren't much lower but when they rise they cool down faster.

John

[t1mrtork]

To NJ Hillbilly,
Where did you get the trans fluid? Do you use synthetic engine oil? If you do when did you start using it. I dont want to start to early and not get the rings seated properly. I build racing engines and we use synth oil very early but the ring seat load is very differnt and if there is oil consumption it dosnt matter as the oil is changed weekly at times.
Terry

[NJ Hillbilly]

The best place to get it and any parts (spin on filters, pan, fluid) is to look for an Allison shop. If You go to their website there is a locator to find an authorized facility. Do not buy filters from the dealer. The trans filter from the dealer is about $16 it's $6 from an Allison dealer. I change mine either every oil change or every other one. Don't forget that there is a magnet on the top of the trans filter. Carefully take it off (it looks like a giant washer) clean and place on new filter. Carefully clean it because it is thin and can break. Fill the filter and install it. I add fluid at about every other filter change to compensate for lost fluid.

I do use synthetic engine oil. I switched to it after the second oil change. I changed the oil and filter at 1000 mi then again at 2500-3000. I put regular oil in in the summer months and run synthetic in the colder months. Look for an auto supply store that deals in AC Delco filters. Get them there stay away from Fram and other aftermarket filters except for Baldwin. The D-Max generates high cold oil pressures and has been known to burst cheap filters.

One other important maintenance item is the rear diff oil. If You have the G80 Eaton Limited slip axle the fluid neds to be changed after about 500 mi of towing or so. The locker uses friction pads like brake pads and during break in the oil gets trashed and dirty. You also use synthetic in the rear. Changing the oil is easy since there is a drain plug in the bottom of the housing, just use a 3/8" ratchet to remove the plug and drain it.


John

[t1mrtork]

John, are you talking about the first 500 miles on the diff? And then normal changes after that?

[NJ Hillbilly]

Wait for 500 mi to tow then tow for about 500 mi then change. To be honest, I am a little anal when it comes to break in and other fluids. I changed at 500 mi.(removed the fluid that was beaten up by the ring and pinion breaking in, there is also a lot of junk from the casting of the housing.), then towed some changed again. then after 2500 mi or so ( I easily towed 500 mi.) I changed it again. I try and do it in the Spring every year. $20 of oil is cheap insurance.

John

[t1mrtork]

Thanks John
Your right most people dont think of the cost of oil that way compared to the cost of working on any of the drivetrain parts.

[Montana_1683]

tlmrtork;

No the tranny temp guage on the dash never changes. Once again Trailer Life Magazine discussed using the overdrive. They stated it didn't hurt the allison tranny. Only suggested never using cruise control when towing, this causes the tranny to shift out of overdrive and by-pass 4th gear. They did mention that if driving very hilly areas and if the tranny begins searching, should then shift to the tow/haul mode. Never had to do this in driving through the flint hills of Kansas or the hills in the Ozarks.

Gary

[t1mrtork]

I see that some people say that they dont use the tow/haul mode very often. The allison book says that it locks up the torque converter, wouldnt that make it more fuel effeicent? Seems like people dont use the tow mode that often. Does the truck pull better when not in the tow mode?

[t1mrtork]

Gimmy2001
Do you find that it pulls better when not in tow mode? Sounds like you dont use it to pull with if you dont have to.

[Montana Sky]

I use the tow mode when in the mountains or town driving. Out on the open road I turn it off to allow the tranny to shift into 5th gear sooner. If the tranny starts "hunting" for gears I turn it back on and let the computer and engine take over. I have found on the open road having the truck in 5th gear sooner I tend to get a little better mileage. And I do mean a "little" better mileage. The tranny will shift into overdrive while the tow mode is on, but for me I found it does not hit 5th until 65-67mph. Tends to run the RPM's closer to 3,000 than I like.

[Montana_1683]

TLMRTORK,
When I am towing in overdrive I don't notice any difference than when I used the Tow/haul mode on a trip to South Dakota. Of course at that time I only had a Prowler TT and used cruise control. Since reading the Article in Trailer Life, should have been April - June 2004. Just prior to getting the Montana. Even in overdrive, when slowing down, the duramax & allison act together like some people describe using an after market exhaust brake. As stated before I wouldn't reccommend using cruise control when towing, as mentioned in the T L article. This causes, in my opinion too much of a downshift and reduces fuel mileage. Wow have I noticed a change in cost to fill up lately. Cost over $56 yesterday, of course this will last 3/4 weeks. Not pulling now since Monty is put away for winter. Last time a fill-up was $43. Can't understand why diesel is so much more than gasoline. It costs less to refine than unleaded.

Gary

[Montana_1683]

tlmrtork,

Forgot to mention that when pulling in overdrive at 65-70 mph the tach runs just above 2000 rpm. Usually gets 12-14 towing, and 18-20 solo. Of course much of the driving around home is rather flat. Do go to Belle Vista, Ark frequently since being a property owner. It is still pretty flat until getting to Joplin, Mo.

[Bear Hunter]

We have an 02 3500 extended cab dually D/A combo pulling a 3255RL. This is our 4th diesel and by far the best. I did call GM about the tendency for the trans to search when under about 65 mph while in tow/haul and was told it would be best to take it out if I would be driving for a prolong time at speeds causeing the trans to search due to it being programed to shift between 62-65 in tow/haul. We use all AmsOil Products in our trucks past and present. Good Luck and Semper Fi
Roger and Lola Cohoe

[t1mrtork]

Thanks for all the advice. I cant wait for spring to arrive to test out the new truck. Sadly the 5er is winterized now. But next fall we hope to be able to try out the trans as we think we would like to go to colorado. Thanks again, Terry

[OntMont]

quote:Originally posted by Bear Hunter

We have an 02 3500 extended cab dually D/A combo pulling a 3255RL. This is our 4th diesel and by far the best. I did call GM about the tendency for the trans to search when under about 65 mph while in tow/haul and was told it would be best to take it out if I would be driving for a prolong time at speeds causeing the trans to search due to it being programed to shift between 62-65 in tow/haul. We use all AmsOil Products in our trucks past and present. Good Luck and Semper Fi
Roger and Lola Cohoe

Our 01 used to do that, but the dealer reprogrammed the computer with an updated version that seems to have eliminated the problem. I'm not sure when GM made the switch, but ours is a late 01, so perhaps the same would apply to your 02. Ask your dealer to check, or just reprogram it to the latest version.

[Bill and Ann]

I had a problem with our truck on the way to Texas this year. The truck wouldn't go over 48 mph. The dealer down here put the gizzmo on the computer and told me all injectors had to be changed. Apparently this is a problem with the Duramax. Thankfully it is going to be a warranty item. There is a 200,000 mile warranty on the injectors. The injectors are a backorder item so I am waiting to get the work done.

[t1mrtork]

Sorry to here about your troubles Bill. I hope the 05 injectors have been made better. Good luck on your fix. If the injectors are backordered this must be the Dmax's weak point. At least the injectors seem to be about the only real problem I have heard about.

[Montana Sky]

Bill,
I had a friend who ran into the same problem as you, they had replaced the injectors with the GM injectors and not even 3,000 miles later he had to have them replace again. This time he got Chevy to use the injectors made by Isuzu for the Duramax, and he claims the motor has never run so strong. I would check into the options offered by General Motors on the injector problem. I just had the high pressure fuel pump replaced on mine as it was leaking into the engine valley. Turned out to be SOP high pressure pump. Was pretty suprised at this happening with only 17,500 miles on the truck and it is not even a year old yet. Good luck on the repair and let us know how it goes.