I recently purchased a 2001 Excursion with a V-10. It has about 148,000 miles on it. I have searched nad read as much as I can on this and I am still . My owners manual specificily says:

MERCON and MERCON V type fluids are not interchangeable.
DO NOT mix MERCON and MERCON V. Use of a transmission
fluid that indicates dual usage (MERCON and MERCON V) in
an automatic transmission application requiring MERCON may
cause transmission damage. Use of any fluid other than the
recommended fluid may cause transmission damage.
I have put hundreds of thousands of miles on my vehicals following the owners manual direction. Yet I see people saying to ignore the manual and use Mercon V, and that the Mercon/Dexron III will damage my transmission. I am about to do a full fluid exchange and filter replacement (DIY found on FTE) Did the Mercon fluid all of a sudden go bad? The Mercon V become derated? I am quite confused.

I liken it to being told "dont drink drano" your entire life then one day "Drink drano and all your worries will go away!"

Will the Mercon/Dexron III actually damage my transmisson? Of is the Mercon V, just better?
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my 04 reads the same thing, but apparently ford did away with regular mercon and now they say that mercon V is approved to use in older trucks. ive been changing my tranny fluid once a year since i bought it new with mercon V and 80k later im still good. i think i read a service bullinton somewhere on it also

 

o and never use mercon/dexron mix EVER that will deffiently give you problems

 

So much misinformation out there...

When your truck was built MERCON was the recommended fluid. That's what the transmission was built with at the factory. MERCON and DEXRON III are so similar that just about any fluid that meets one of the specs also meets the other. So any fluid that is MERCON/DEXRON III will work just fine.

In 2006(?) Ford eliminated MERCON and GM eliminated DEXRON III. Ford respec'd MERCON V so that it is compatible with older transmissions that were designed for MERCON. So now MERCON V is the recommended fluid for your transmission.

In reality and fluid that is MERCON, MERCON/DEXRON III, or MERCON V will work fine. My first choice would be MERCON V because it is a better fluid.

 

WOuld it cause an issue if I topped it off (it was a quart low) with Mercon/Dexron III? I have no idea what fluid was in it.

 

No, that would not cause a problem.

 

Hey Mark,

While we're talking about it, what is your preferred brand of Mercon V in the 4R100? Any real advantages in your opinion of one fluid over the other?

Very Respectfully,
Mike

 

Mark,
Do you know if they changed the formula of the fluid when they respec'd it? The reason I ask is that I have some Mercon V that I bought several years ago and I wondered about compatability with the newer Mercon V. Is there a spec number for the old and the new that I could compare for compatability?
Thanks.

 

great post EMC. just went through this myself........and I discovered just what Mark and the others are saying. Thanks much fellas for the help!

 

I like Mobil 1 Synthetic ATF.

Yes, the formula was changed. Older MERCON V is different and is not compatible with a 4R100.

 

That's what I suspected. Thanks for the confirmation.

 

Reps for Mark