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Mickeyfan0805's avatar
Mickeyfan0805
Explorer
Jul 22, 2013

Adding ATF when you don't know what's in there

We had our transmission fluid flushed and replaced last spring and, being the non-mechanical idiot that I am, I didn't ask for detail as to what they filled it with. Since I didn't ask for synthetic, I'm assuming it was conventional fluid, but don't know for sure. I like to carry spare fluids in the truck just in case, but I don't know what to get. Can I top-off with synthetic if it currently filled with conventional or should I just assume it's conventional and stay with it?

Also, can anyone please explain the whole merc V/Dex thing? I don't have the manual here at work and I don't understand exactly what I need (I see regular, Merc V, Dex/Merc V). I have a 2006 Suburban 2500 with an 8.1L engine.

Thanks!
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  • Perrysburg_Dodg's avatar
    Perrysburg_Dodg
    Explorer
    Jul 22, 2013
    I do believe all AT from 2001 and up is a full syn oil isn't it. All Chrysler ATF fluid is anyway, bet GM and Ford are the same.

    Don
  • jfkmk's avatar
    jfkmk
    Explorer
    Jul 22, 2013
    2006 should use Dexron VI. They are not backwards compatible, so you can't use the previous versions of Dexron. I would buy a quart of the Dexron VI as a spare.
  • Gale_Hawkins's avatar
    Gale_Hawkins
    Explorer
    Jul 22, 2013
    RCMAN46 wrote:
    Dexron VI is not backward compatible for Allison 1000 prior to 2006. Transynd is best for all of the Allison 1000 transmissions. Your best bet is go with the owners manual and hope the proper fluid was used during the transmission service.


    Good point. Dexron VI is spec for GM transmissions and not other brands. I the early years Allison used some O-rings I heard that last OK with Dexron III but not VI.
  • RCMAN46's avatar
    RCMAN46
    Explorer
    Jul 22, 2013
    Dexron VI is not backward compatible for Allison 1000 prior to 2006. Transynd is best for all of the Allison 1000 transmissions. Your best bet is go with the owners manual and hope the proper fluid was used during the transmission service.
  • Gale_Hawkins's avatar
    Gale_Hawkins
    Explorer
    Jul 22, 2013
    We carry a quart of Dexron VI from WM for any GM product we own. The MH is a 1992.
  • john_bet's avatar
    john_bet
    Explorer II
    Jul 22, 2013
    If you do not have the receipt or it not listed just call the dealer or whom ever and ask what they used.
  • BurbMan's avatar
    BurbMan
    Explorer III
    Jul 22, 2013
    Your owner's manual should specify Dexron VI for the 4L85E transmission in your truck. Dex VI is synthetic, so there is no "regular fluid". Dex/Merc is a fitzall fluid for older GM's that use Dexron III and Fords that use Mercon.

    GM went to Dexron VI in 2003-ish and Dexron III is now discontinued. Dex VI is now the only GM-approved fluid and is designed to be backwards compatible with all GM transmissions.

    I did a flush/fill with filter change early this year and just did all of this research. I used Dex VI and have had no issues.

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