I work at a farm equipment dealership and we sell an automatic transmission oil that on the back it says Allison C4 approved. I know a couple guys that are running this fluid in their duramax allison. Was wondering if this sounds like an ok idea to you guys. Thanks in advance.

Call Allison and ask them.

http://www.allisontransmission.com/service/autoapp/172/

A good bit of reading. Too much to copy and paste.

In a nutshell...C4 is an outdated standard. That does not mean that it is not good fluid. The C4 approved list was essentially replaced by Schedule One TES-389 approved list, and then there is the cream of the crop, TES-295 approved list.

The ATF fluid options: detailed information (http://www.dieselplace.com/forum/showthread.php?t=302701) sticky has a lot of good info also.

Here are the TES 295 fluids. Except for Mobil Delvac, all of them are actually Transynd under a different brand name. If it is really Allison approved, it will have the Allison logo on it.

TranSynd
Autran Syn 295
Emgard 2805
Fleetrite Synthetic ATF
Mobil Delvac Synthetic ATF
HD SynTran

This is mainly for future searchers:

I did a little more research on "Allison C4 Approved." Most of the Dexron III fluids that are available at local auto stores are C4 approved. There are hundreds of products that are "C4 Approved". But, most of them aren't even ATF. The C4 approval is used for ATF, Engine Oil, and Hydraulic Oils. I went to the local NAPA, and looked at the 5gal buckets that they had stacked up by the reset of the oil. They were all kinda mixed together. Valvoline Dex/Merc, No Name 10w-30 Engine oil, and a NAPA Brand Hydraulic Oil (10w-20). All stating Allison C4 Approved. The Hydraulic Oil, in the description, states: "For use in transmissions, gearboxes,.....". Just because it says "Allison Approved" and "For use in transmissions" doesn't mean that it is for use in your Allison 1000. There are a lot of Allison transmissions that dont even use ATF. The M1 Abrams Tank has an automatic Allison Trans, and we use 15w-40 or 30wt. Go figure.

Here are the TES 295 fluids. Except for Mobil Delvac, all of them are actually Transynd under a different brand name. If it is really Allison approved, it will have the Allison logo on it.

TranSynd
Autran Syn 295
Emgard 2805
Fleetrite Synthetic ATF
Mobil Delvac Synthetic ATF
HD SynTran

BTW, The HD SynTran is a John Deere product.

Dont want to steal your thread but what if you just want to top off your tranny after a spin filter change, mine is a 2010, what do i use?:confused:

Factory fill is Dexron VI. Fluid loss on a filter change is ~1/2 quart.

The Allison C4 fluid rating is worthless as its outdated and way too broad. Fluids meeting these specs can be basically anything from ATF to hydraulic fluid to engine oil. C4 (only) rated fluids are no longer approved for use in Allison Commercial On-Highway products and C4 fluids were never approved for use in the 1000/2000 Series transmission. Note that some good fluids MAY have the C4 rating, as the C4 rating is broad it does not make a fluid good or bad, the rating is obsolete, so just ignore it.