Mercon V vs Dex III Mercon

[hominid7]

I recently had my transmission fluid flushed. While my owners manual calls for DexIIIMercon, as we all know, it has since been replaced by Mercon V. I had my transmission fluid flushed at a local shop however and went with the same old Formula Shell Dex III Mercon + Lubegard Red that i've been using with success for the last 2 transmission flushes. The car now has 85,000 miles on it and i've been keeping it flushed at around 25-30K mile intervals.

Prior to making this decision i did some reading on the various fluids and was wondering why, since Mercon V is newer and part-synthetic, it is also higher viscosity (thicker) at operating temperature, has a lower flash point and almost the same pour point as the old DexIIIMercon? I'm not seeing the benefits for upgrading to the new Mercon V.

Am i missing something?

FWIW, my old fluid, with 30,000 miles on it, was still bright red, didn't smell burnt, and in doing the blotter test, looked fine. The car sees a lot of short trips mixed with long stretches of highway use. It runs around 3000 RPM at 72 mph.

 

[Ben99GT]

Depends on which Mercon V you're talking about, the Mercon V spec was primarily an improvement in shear stability.

Look at the specs on Redline's Mercon V fluid (D4)

7.5 cSt @ 100 deg (C)
437 deg (F) flash point
-76 deg (F) pour point

 

[bluestream]

As said above, Mercon V will last longer between changes as it has a better base stock. Also, take the fluid you drain out and put it in a clear jug. You will see particulates settle out to the bottom after sitting a while.

 

[hominid7]

Wow...Redline's Mercon V is indeed impressive!

I was looking at Shell's Mercon V vs Dexron/Mercon

MercV - DexIII/Mercon

8.4 vs 7.2 100*C

(-42*C) vs (-45*C) Pour Point

190*C vs 220*C Flash Point

I guess not all Mercon V's are created equally

Data source:

http://www-static.shell.com/static/can-en/downloads/shell_for_businesses/oils_lubricants/1-33.pdf

 

[hominid7]

Originally Posted By: Bluestream
As said above, Mercon V will last longer between changes as it has a better base stock. Also, take the fluid you drain out and put it in a clear jug. You will see particulates settle out to the bottom after sitting a while.


I'm sure you're right, i was just impressed that with 30,000 miles the old DexIII/Mercon still looked to be in good shape. The technition actually told me if it was his car he would not change it. However Mazda has a not so great rep with the transmission in my car, so i've been keeping it changed regularly.

Having said that, perhaps the addition of Lubegard Red turned my old Dex/merc into something more along the lines of a Mercon V ?

Transmission is still very smooth, quiet, and has not given me any trouble, and i hope it stays that way for some time to come.

I have been using Pennzoil Multi-Purpose ATF, which is rated Mercon V, in the power steering (it calls for ATF).

 

[bluestream]

Sounds like you are doing the right thing. Remember most people never change the AFT ever

 

[caravanmike]

Originally Posted By: hominid7

However Mazda has a not so great rep with the transmission in my car, so i've been keeping it changed regularly.





all of the cd4e problems ,from94,94,96 had been worked out by 2001. but keeping it changed regularly is recommended in any car, whether it "looks" good or not. glad you didn't listen to the tech!

 

[hominid7]

Originally Posted By: caravanmike

all of the cd4e problems ,from94,94,96 had been worked out by 2001. but keeping it changed regularly is recommended in any car, whether it "looks" good or not. glad you didn't listen to the tech!


That's good to hear. Mine is the V6 and has the GF4A-EL, however i've read that all models should be flushed regularly as they all tend to be a little harder on trans oil than others. Hopefully mine will last as long as i need it to