# What's Up With That? ... (GM & Dexron III & Dexron VI)

**URL:** <https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185>\
**Category:** Maintenance/Repairs\
**Tags:** fluids\
**Created:** [November 17, 2008, 4:40pm UTC](https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185 "2008-11-17T16:40:48Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\
**Post date:** [November 17, 2008, 4:40pm UTC](https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185/1 "2008-11-17T16:40:48Z")

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Some GM cars call for Dexron III automatic transmission fluid. Dexron VI is now on the market, and as I understand it, is required in some six-speed automatic transmissions.  
  
  
  
 Is Dexron VI a suitable, or even desirable, substitute for Dexron III, in say, a 4-speed auto?  
  
  
  
 Where I live, Dexron III is hard to find. Is Dexron III being phased out following the introduction of Dexron VI?  
  
  
  
 Any insight would be appreciated!

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**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\
**Post date:** [November 17, 2008, 6:43pm UTC](https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185/2 "2008-11-17T18:43:59Z")

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Maybe…maybe NOT. Most of the time it’s backward compatible…but sometimes it’s not. Check with the Dealer to know if it’s compatible. DON’T go by what the manufacturer of the Dexton fluid says.

Example…Granted I’m talking about gear oil here…but same problem. My 98 Pathfinder requires SL-4 gear oil for the 5-speed manual. Sl-5 is out and according to all the documentation it’s suppose to be compatible with vehicles that require SL-4…IT’S NOT. In fact Nissan has a nice service bulletin on it…saying DO NOT USE SL-5. IT WILL DESTROY THE SYNCRO’S IN A TRANNY THAT REQUIRES SL-4.

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**Author:** ![jayhawkroy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/jayhawkroy/32/33_2.png) [@jayhawkroy](https://community.cartalk.com/u/jayhawkroy)\
**Post date:** [November 17, 2008, 7:46pm UTC](https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185/3 "2008-11-17T19:46:39Z")

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My understanding is that Dexron VI is backwards compatible 100%.  
However, my current solution is to use a universal ATF that states it is Dexron III and Mercon compatible. Have done this for 100+K miles on my wife’s Subaru with no issues. My mechanic is taking the same tack on his ATF changes, also.

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**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\
**Post date:** [November 18, 2008, 1:12am UTC](https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185/4 "2008-11-18T01:12:53Z")

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Thanks For The Responses. I Did Notice That The Dexron VI Says "Fully Synthetic."  
I think the original Dexron III, is not.

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**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\
**Post date:** [November 18, 2008, 2:49pm UTC](https://community.cartalk.com/t/whats-up-with-that-gm-dexron-iii-dexron-vi/22185/5 "2008-11-18T14:49:38Z")

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> My understanding is that Dexron VI is backwards compatible 100%.

Yup…suppose to be…SL-5 is SUPPOSE to be 100% backward compatible…IT’S NOT.