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Changing Fluids in my GMC Sierra 2500 HD Duramax 4x4?

Truck Trend
Posts: 4666
Joined: 02/07
Posted: 01/07/09 02:22 PM

Changing Fluids in my Truck

Question: I have a GMC Sierra 2500 HD Duramax 4x4 with a 6-speed standard gearbox.  I bought it new in 2001 and now have 98 000 miles on it.  Over the years I always made sure that the maintenance was done as per the owner manual but something bugs me.  Nowhere in the schedule maintenance does it talk about gearbox oil change.  They cover the engine oil, the engine coolant system and all kinds of minor items but they never talk about the standard transmission, the transfer case, the rear and front differentials, and what about the power steering and the hydraulic clutch?  How many years can we go without replacing the oil in all these components?  I understand that they use synthetic oil these days but are these synthetic oils good for the life of the truck?

Answer: I scanned through several related model year GMC pickup service schedules, specifically the Duramax Diesel owner's manual supplements, and I see where you're coming from. According to General Motors there's no need to change the 6-speed manual transmission fluid or the transfer case fluid (unless you have an automatic), and you should periodically check, top-off, but never replace the front or rear axle fluids. Engineers believe that under “normal operation” the synthetic lubricants will hold up indefinitely, or at least as long as the predicted lifespan of the truck. The advanced lubricity and thermal resistance of synthetics outweigh that of petroleum based products, and the manual transmission, transfer case and axles are sealed (or nearly sealed) components which limit or eliminate incoming contaminates?such as normal blow-by gasses into engine oil. Drivetrain technology has also lightened the load on lubricants by lessening internal friction. As far as brake fluid, clutch fluid or power steering fluid replacement, nowadays they're not typically part of a manufacturer's maintenance schedule. With all that said, if it's my truck and I want to keep it for a long time, I would try not to let any drivetrain fluid go far beyond the 100,000 mile mark. Of course, this is just an opinion. If you agree, go to GMC service and be sure to use the correct replacement fluids. There may be updates since your owner's manual went to print. Dealership service department's maintenance schedules also often disagree with that of the manufacturer.


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Posts: 599
Joined: 07/08
Posted: 01/07/09 06:59 PM

Interesting stuff. I figured when they started sealing grease systems and extending drain intervals, stuff like this was bound to happen, and would start to include any fluid. Now when manufacturers start to say you don't have to change ATF or engine oil anymore, then I'll start paying attention.  

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New User
Posts: 1
Joined: 01/09
Posted: 01/12/09 10:09 PM

There's much more to this subject than meets the eye.  I stumbled across this question today while doing a search, and thought I could help clarify.  I'm a Mechanical Engineer with an '02 2500HD Duramax, and have spent the last decade in the automotive industry supplying to most of the OEM assembly plants.  I speak fairly regularly with an OEM GM engineer, who also has a Duramax, and we worked together in his shop installing remote bypass filter kits on our Duramax 6.6 engines.

For maximum vehicle life, OEM powertrain engineers (in general vehicle terms, rather than in Owner’s Manuals or Service Manuals) recommend changing ALL lubrication fluids in the first 2,000 to 4,000 miles of service.  This is generally because of the high operating temperatures and high wear-particle content generated during the break-in period, which break down and contaminate the lubricants.  Changing the fluid during this time, instead of at the factory-recommended intervals, can double to quadruple system life. Going to a high quality synthetic will at least double it again (NOT all of them are "factory fill" synthetics, as is often rumored).  For example, the front diff fill cap on 2500HD 4x4's through some 2004 models are not designed to have long-term compatibility with synthetics, which should tell you something about the factory fluid.  I forget which is which, but one is white, the other black.  You'll need to order the correct one to go synthetic up front.  

It goes back to "planned obsolescence". Current material finish and surface technologies allow slower wear, so that non-commercial users will make it past warranty with the factory drivetrain fluids, and commercial users will pay for diff and tranny failures that aren't covered under warranty for commercial use.
You can download a very interesting Research White Paper here on Gear Lubes - as far as I'm aware, the most authoritative testing ever published:  Gear Lube White Paper

If you note the background info in the first section you'll start to get a good idea of reality on differential failures, which also translates to tranny and transfer case failures: most of them fail, in truth, because their lubricants failed long ago. As as you'll see in the test data comparing those 14 gear lubes, just because it's "synthetic" doesn't mean it's high performance.

My Duramax purchase was a pivotal event for me because it sparked my shocked research to discover how easy it is to run 500k-1M miles as a 5th wheel tow vehicle... without drivetrain failures (I'm not going to vouch for injectors and fuel pumps, nor for offroading, etc.)  Many truck owners, like myself, plan to keep it for a very long time. If you're in that group, I recommend that you change everything to true synthetics, and don't use dealer fluids. Contrary to so many online forum postings around the web, the use of a dramatically superior synthetic lubricant is a dramatically superior choice that does NOT cause failures nor cause the OEM to deny warranty coverage, and Dealer service managers who claim otherwise are simply wrong.

And beware having a GM dealer change your transmission fluid: very few even carry a fluid that meets the Allison TES-295 spec.  I negotiated the fluid-exchange fee for bringing my own fluid to the Dealer.  Less than a mile from each other, my GM dealer didn't recommend using a synthetic in the Allison, while the commercial fleet center knew that Allison's extended commercial warranty required a high-performance synthetic - but still didn't carry it or use it.  It's eye-opening for a fleet to learn that Allison’s expensive extended warranty requires the expensive synthetic fluid, but that the fluid itself reduces tranny failures by way over 90%.  Hint - there are only two fluids that meet TES-295, and Allison lists only the one they’re partners with.

(Yeh, unfortunately very few people know this stuff… outside of lubrication, drivetrain, or reliability/maintenance engineers. Any vehicle can be a 500k+ mile vehicle, but it’s just not in the OEM’s or oil-drilling companies' best financial interests to explain how.  Hope this is helpful.  I can't guarantee how often I'll check the forum, but you can reach me at BrianDMT@bwwonline-dot-com)  
Sierra 2500HD D/A
Diesel Turbo Life Saver
Amsoil Nanofiber Remote Bypass Filtration and over 60k miles since last oil change

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