Just bought a 2005, 2500HD, Diesel, 4x4, crewcab, shortbed, 3.73 with the Allison automatic. My experience with diesels is NONEXISTENT, having always used gasoline vehicles... So, I've got some naive new user questions:


With a gas truck, at about 1000 miles I'd change the oil to get rid of the filings and crap from the machining. Do I do the same thing with a diesel?


We'll be towing a small 5th wheel - about 6500 lbs, and the normal amount of additional junk in the backseat and truck bed. With my previous truck this was considered "severe" duty and I changed the oil every 3000 miles, had the transmission serviced every 12,000 miles, and had the differential fluid changed every 12,000. For the diesel do I go by the oil life indicator? Even with the towing? Or is there a different interval at which the oil should be changed? Transmission serviced? Differentials? I'm always leery of what the manuals show as service intervals, so I'm wondering if they're too optimistic...


Synthetic lubricants - Are there significant benefits on this truck to using synthetics in the Allison and/or the differentials? Does a synthetic oil even exist for the Duramax? If so, is there any benefit to using it? Are there warranty concerns? If synthetics are recommended, are there any particular brands that are best?


Gauges - Since we tow, and frequently tow thru the Rocky Mtns and into the Canadian Rockies is there benefit to adding an exhaust temperature gauge and/or a turbo boost gauge? If so, is there a particular brand/set that is recommended?


Tire Pressure - the door says the pressure should be 55 lbs on the front and 85 on the rear. I presume the 85 is for a full load in the bed. What should I be running when the truck is empty - 50 in the rear? 55, same as the front? Since our trailer is only around 950 lbs on the kingpin, same question. When we've got the trailer on what should I be running in the rear?

Frequent oil changes are certainly advised in the diesel. Synthetics are beneficial.Follow your same procedures, except you may want to try an earlier diff fluid change.


The tire pressure lables are more for legality. I run 45 in the front and 55 in the back with a slightly less towing weight.





Have fun; you will love the truck.

The tire pressure question is interesting. I also have a 2005 2500HD. While thumbing through the owners manual if cam a cross a couple pages that looked a little thicker than normal. I looked them and noticed that they had a sticker stuck over them.


I think the sticker over the page has inflation instructions that just mirrors what is on the door label which is like 55 front and 80 back.


I slowly pulled the sticker off without ripping the page beneath and from what I recall, the original page talks about different inflation based on load. Guess the lawyers didn't get to read the manual until after it was printed.


By the way, mine came with 60 front and back. Aired the back up to 80 and went for a ride to see how it would ride. Quite bouncy!

I had 60 front and 80 back on my stock 245 tires...Steeltex from Firestone. WOW, what a crappy ride over train tracks and rough streets. I don't tow anything crazy, so I got some Dunlop Radial Rovers/Load range D. Some have said they have tread squirm with Dunlops from the weight of the truck, but I have had good luck with these.

Yes, change oil early and change diff early, but top it off NOW. The diffs are always low off the lot, so fill them both. Use the search feature and read, read, read. Another guy asked some of the same questions not long ago http://dieselplace.com/forum/forum_posts.asp?TID=15165. I run 55 all the way around when not loaded. You can probably stay there or go up to 60-70 on the rears when towing. Adjust based on tire contact and ride. You don't need to be beat to death or wear out the center of the tire in a week. Edited by: chuntag95

Thanks for the pointer. I found and read the info...


The truck came with 45 in the front, and 70 in the rear. Just for fun I pushed it to 80 the other day and went for a drive... Then came back and dropped it to 55 and went off to see if my kidneys still worked! I raised the front to 55 as recommended by the factory and put 70 in the back when we put the trailer on and that worked really nice.


If I'm reading things right, changing oil at 1500-2000 initially is a good idea. And at 5K or 10K going to synthetic oil is good. Recommendations for brand/weight? I presume I can't use the Mobil1 I was using in the Dodge in the diesel?


I'll check both differentials in the morning. And top up if needed. And I'll change both at 1500-2000 and go to synthetic... In this case it appears that I CAN use the Mobil 1 synthetic gear lube? And since this is a locker I presume I don't need the limited slip snot anymore?


I didn't see anything specific about gauges... Worthwhile adding the EGT and boost or not?


One NEW question... Lights. When I hit the brights, the regular headlights go off. And when I hit the brights the fog lights ALSO go off. On the Dodge there was a relay to jump to keep the regular headlights on WITH the brights. And the fog lights. I'd like to do this. Can somebody who knows the setup or these tell me what has to be done so turning on the brights doesn't shut everything else off?

You can use Mobil, but NOT Mobil 1. Mobil Truck&SUV in 5W-40 is supposedly the same as Mobil Delvac 1 which IS for our trucks (in case you can't find the Delvac 1 locally).

Re: The lights. Yes you can have the low and high beams on at the same time. Do a search; there are several threads on it. Edited by: Kartattack

Engine oil questions ---- read http://www.blackstone-labs.com/ (http://www.blackstone-labs.com/)


Transmission questions----- http://www.allisontransmission.com/service/faq/index.jsp?Cat (http://www.allisontransmission.com/service/faq/index.jsp?CategoryID=11) egoryID=11


Transmission fluid (Ask for the Allison document titled " Time In A Bottle"....!!!!!! It says it all... http://www.allisontransmission.com/service/autoapp172/index (http://www.allisontransmission.com/service/autoapp172/index.jsp). jsp


These sites are the best resources I could find after extensive research.


enjoy....


Harold