Mercon V vs. Dexron III?

[bfg9k]

My 98 Subaru Legacy recently had a complete overhaul on its auto transmission. According to the shop, the previous owner had treated it with a conditioner that caused the seals to swell (to prevent slip) and eventually turn brittle and crack.

The rebuilt tranny is running great, but one oddity: the shop uses Mercon V fluid, but the manual calls for Dexron III. Since this shop is an indy recommended by my very good mechanic, and has been in business for 50 years, I assume he knows what he's doing

I'll be adding a transmission cooler this spring for added insurance. After the one year warranty is up I plan on filling with Amsoil synthetic ATF, but in the mean time are the Mercon V/Dexron III fluids mutually exclusive in their application??

 

[medic]

What brand of Mercon V did they use? Some Mercon V fluids are also spec'd for Dexron.

For example, AAMCO Mercon V is spec'd for Ford Mercon V & Mercon along with GM Dexron III, Dexron IIE, & Dexron II.

Castrol Mercon V is only Mercon V and Mercon.

I would bet that most tranny shops only keep 2 or 3 bulk fluids in stock that meet multiple specs. This prevents them from having to keep multiple fluids on hand and probably cuts the bottom line just a bit, allowing them to make more $$$ or pass additional saving onto the customer.

 

[RF Overlord]

bfg9k, I'd be careful about using Mercon V in an application that it's not spec'd for...I'm not a transmission engineer, but a fellow named Jerry Wroblewski IS...he helped design the Ford 4R70W and HIS advice is that Mercon V can be safely used in all years of that transmission (and the AODE), even if plain Mercon was originally spec'd, but NOT to use it in other transmissions that don't specifically call for it. Now, he was talking about other FORD transmissions, so I can't say if his advice is valid for your Scooby-Doo

...maybe you should try some of the Subaru boards and see what they say...

 

[Sin City]

Like medic said some fluids are rated for both Mercon V and Dexron III. Most likely the shop that performed the work on your Subaru used a fluid that is rated for both. Now that the new Dexron III "H" fluid is out it makes sense to produce a fluid that is rated for both Mercon V and Dexron III. The fluids are not all that different and it makes life easier for everyone.

 

[bfg9k]

You folks were right. I called the shop the morning and asked. They use a compatible ATF that's rated for both Mercon V & Dexron III - I guess the owner just calls it Mercon V out of habit.