2004 2500 Suburban 6.0 - Full Syn Fluids Replacement

[Heartbeat Hauler]

My wife's 04 2500 Sub is due for service. I would like to change everything over to synthetic fluids, engine, trans, frnt & rear diffs, and Xfer case. Any recommendations? It's still under warranty so it's gotta be kosher with GM.

Engine -
Trans -
Frnt & rear diffs -
Xfer case -

What say you?

JP

[DmaxMaverick]

Good idea, IMO, going to synthetic. I use and recommend Amsoil, but Mobil 1 also gets a vote of confidence. Other brands, Royal Purple, Redline, etc. also have good products, but I have not used their full line of products. You may need to use GM's transfer case fluid. Check the manual, it should be Autotrac II fluid if it has "Auto 4x4". If it has only push button 4x4 without the "Auto 4x4" button, or it's a 2wd, it will need the same fluid as the tranny, Dexron III. GM won't have anything to say about the brand of lubes you use, as long as they are of the right type/grade/weight.

My lube shopping list for the Sub would be:
Amsoil 10w-30 engine oil
Amsoil 75-90 "Severe Gear" diff lube
Amsoil Universal ATF for the tranny (and possibly the TC)
GM Autotrac II fluid for the auto transfer case

Mobil 1 also offers the same fluids, and they may be more available.

[Heartbeat Hauler]

Thanks for the info. I know the Amsoil is good stuff, but it really doesn't have the "Seal of Approval" for meeting GM specs. The sub is a 2500 4x4 and it does have the Auto 4x4 button....which means I guess it needs the Dexron III in the xfer case, or can I go to the Dexron VI in both the tranny and the xfer case?

JP

[DmaxMaverick]

Don't know what you mean by "seal of approval", it simply doesn't exist. GM can only require types, grades and minimum standards of service products. Amsoil products meet or exceed GM's requirements, within the respective types/grades. Several other major brands (like Mobil, Shell, Chevron) have products that don't carry the API seal. This doesn't mean the lubes don't meet the requirements. I'm not pitching a brand or type of oil, just clearing a misconception.

If it has the "Auto 4x4" button, it needs Autotrac II fluid. It should have the NP246 TC, which requires it. Confirm this with your manual, or the dealer.

Dexron VI should be fine for the tranny. GM states it is backward compatible with previous Dexron III equipped vehicles. Your choice.

[Heartbeat Hauler]

Cool. Is there some gain to be had by using the Dex VI in the tranny? I'm looking to try and help fuel mileage as well as durability, which is why I want to also use syn in the diffs and xfer case.

What I meant by seal of approval was that GM requires a GL-5 for gear oil and I was under the impression that AMSOIL would not pay the exorbitant price to get that test. With all the crap that is happening at GM and the rotating door used for service-writers at my dealership I would hate to loose my warranty because of some BS designation on my gear oil. I guess they wouldn't be able to tell the difference so maybe it's really not an issue.

JP

[DmaxMaverick]

GL-5 is just a minimum standard for gear lube. Amsoil Severe Gear lube is GL-5 rated. GM will have nothing to say about using it. They can't, legally. If for any reason GM denies repairing a failure, claiming the lube caused it, Amsoil will send their tech's and lawyers to have a talk with them. If it is agreed that Amsoil lube was at fault, they will make good on the repairs. That's their policy with all their products. Amsoil rates their products in accordance with the same standards, with or without an API stamp.

As far as I know, the jury is still out on the Dex-VI. If you are using full synthetic, it won't matter, in any case with either.

[Heartbeat Hauler]

Thanks man. I apprecaite the responses. There is so much info out there, not all credible. I always feel like I get the straight scoop here.

JP