Reasons not to use Mercon V vs Dex/Mercon III ?

[hominid7]

Sometime in the near future i will be attempting my first DIY auto tranny flush via the bucket method.

My 2001 car came with Dexron/Mercon III from the factory. Any reason i should not 'upgrade' to Mercon V?

Also, regardless of going with DexIII vs Mercon V is there a brand or brands that stand out above the rest as far as quality goes or is Walmart supertech ATF as good as any other?

In my area the following are readily available:

Pennzoil Dex/Mer III
Pennzoil Mercon V (multi vehicle synth blend)
Castrol Dex/Mer III
Castrol Mercon V
Coastal Dex/Mer III
Coastal Multi-Vehicle Mercon V synth blend
Walmart Supertech Dex/Mer III
Walmart Supertech Merc V Multi Vehicle Synth blend
Valvoline Dex/Merc III high mileage
Walmart Supertech Dex/Merc III high mileage

Suggestions?

Thanks!

 

[unDummy]

You'd benefit for the synth blend.

I see it like this: why even bother with DexIII/Mercon when superior MerconV has been out for a decade already!

 

[bdai]

Switching to Mercon V caused problems with some (but not all) CD4E transmissions used in the Ford Escape. Ford back-spec'd Mercon V for that transmission regardless, probably because they had no other fluid to pick.

You might want to check a Mazda 626 forum to see if there are any issues. I took the (arguably) safer route and switched to Dexron VI instead.

 

[hominid7]

Thanks for the recommendations. If i take my car to the mazda dealer they will use Mercon V as the replacement for Dexron/Mercon III. My 626 is the V6, so i have the "Mazda" tranny not the ford (thankfully).

I'd save a few bucks by going with Dex III vs Mercon V. If all goes well with the flush i plan to do it myself every 1 to 2 years, so my thinking was that the extra expense of Mercon V may not be worth it if doing flushes more often. I have confidence in the Castrol Dexron/Mercon III, but if spending an extra 20 bucks a year gives me a LOT more protection on my tranny it may be worth it.

 

[The Critic]

Many Mercon-V fluids are also dual-certified for Mercon as well.

 

[ewetho]

Ford now just uses the new

Mercon
Mercon V/DexronIII H Spec oil.

Use it in everything from Power Steering to Manual Transmissions and Automatic Transmissions.

Use it and forget about it. Want a full synthetic try Amsoil or Redline.