# Transmission fluid ATF+3 vs. Dexron III / Mercron **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 21, 2008, 9:29pm UTC](https://community.cartalk.com/t/transmission-fluid-atf-3-vs-dexron-iii-mercron/15666 "2008-06-21T21:29:44Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![jmturner](https://avatars.discourse-cdn.com/v4/letter/j/aca169/32.png) [@jmturner](https://community.cartalk.com/u/jmturner)\ **Post date:** [June 21, 2008, 9:29pm UTC](https://community.cartalk.com/t/transmission-fluid-atf-3-vs-dexron-iii-mercron/15666/1 "2008-06-21T21:29:44Z")
Are the two compatible? Whats the real difference? I recently changed my fluid on a Dodge Ram 2500 (2003)with a 48RE transmission built by Suncoast transmission. The fluid that my mechanic put in it was ATF +3 when it was installed. I called Suncoast and they recommended using Dexron III/Mercron. I did not flush the system as I should have and believe that there were several quarts of the old fluid left in system. Is this going to be a problem? It shifts ok and there are no signs of any problems. This is a very expensive tranny and I need to be sure. ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [June 22, 2008, 1:59am UTC](https://community.cartalk.com/t/transmission-fluid-atf-3-vs-dexron-iii-mercron/15666/2 "2008-06-22T01:59:41Z")
No, these are NOT the same, and your transmission requires Chrysler-specified fluid. ATF+3 is no longer being made, and has been superseded by ATF+4 in all applications. It is synthetic-based, and has more resistance to heat and breakdown than ATF+3. ---
**Author:** ![MG-McAnick](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mg-mcanick/32/188_2.png) [@MG-McAnick](https://community.cartalk.com/u/MG-McAnick)\ **Post date:** [June 22, 2008, 2:34am UTC](https://community.cartalk.com/t/transmission-fluid-atf-3-vs-dexron-iii-mercron/15666/3 "2008-06-22T02:34:53Z")
You must have talked to a general flunky at Suncoast transmissions. Anyone who knows anything about fairly late Chryco trannys knows that they require ATF +3 which has now been superceded by ATF +4. If indeed THEY told you to use D/M, then they owe you a complete flush and fill. Do it ASAP.