My Truck takes mercon V.. I bought 12 qts of Castrol Transmax/Dex/Merc from Walmart about $45 for the lot.. I removed rusted cooler lines from the truck and now I want to purge the rest of the fluid with out wasting the motocraft mercon V that I already have... My goal is to run the castrol/merc completely through and out the system while I have the cooler lines open. This would be a partial drain of some of the old fluid hoping to get some of it out of the touque converter... I would end up refiling the tranny with Mercon V.. shoud I do this or not??

 

How old is the fluid that is in the transmission? (miles) Why a partial flush? If your in for 12 qts how much more for a full flush?

 

No you should not since it's listed as being compatible with Mercon, but not Mercon V. I know it's tempting to save a few bucks but if you think tranny fluid is expensive, try paying for a rebuild.

 

Ok, my 03 expedition currently has a transmission issue...one of the cooler lines rusted and broke ..The truck lost a lot of fluid and would not move into drive or reverse this all happened in my driveway..The cooler line from the radiator to the
cooler broke..the other two lines going to the transmission are deeply rusted..so I bought new lines.. and plan to replace.. but first I wanted to replace the lost fluid with the castrol Trasnmax/dex/merc just as a purging..I didn't plan on leaving the castrol in the tranny.. I have 14qts of Mercon V.. that I a prepared to use.....should I go forward with this idea?

 

If you're confident you can get virtually all of the Transmax out then go for it. My only concern would be if the two fluids can be mixed should any of the Transmax remain.

 

Thanks for the response... my concern too was the blend of the two different fluids...I was thinking to use two bottles of the Transmax and three of Mercon V..run this oil through and then close up the lines..drop the pan change filter
close up everything and then put only the Mercon V.. I was prepared to get a rebuild so this would be my last attempt to restore the tranny. How much damage could be done to the transmission that is not performing. Im in NY temperature here is 97 degrees..I break a sweat just thinking about crawling under my truck

 

The fluid in the transmission I never changed it during the 13 years that I've own the truck.. I will drop the pan and see if it's ever been serviced

 

Just wanted to add that @Mark Kovalsky has said in the past that a flush will remove virtually all of the existing fluid in a transmission. Here's a link to the procedure he wrote for us 15 years ago, and I'm tagging him to see if he has any thoughts on mixing Dex/Merc with Mercon V

https://www.ford-trucks.com/articles...-transmission/

 

They mix just fine, but if you use the procedure you'll get about 95% new fluid in the trans when you're done.

Running Dex/Merc in this transmission (it's a 4R70W) is inviting torque converter shudder into your torque converter. I would not use any Dex/Merc in a 4R70W.

 

Thanks, The Dex/Mercon will not stay in the truck longer than just running it through the lines to help push out the old fluid... maybe this is not the best idea but I figured what do I have to loose when the transmission had recently failed..because of very low fluid... So my next step is to replace to lines that run from the transmission to the radiator and the cooler, drop the pan replace filter..then refill with only!! Mercon V.. I'm hoping and having a good feeling the transmission will be restored... I guess I will get a good indication of how bad thing are once I look on the inside of the pan.. hopfully not chunks of metal

 

My Agenda for tomorrow is to replace the two lines on the transmission side .. at this point the vehcle is sitting on jacks in my driveway .. I just replaced a line from radiator to cooler.. look good no leakes… The vehicle is filled with dex/merc.. I let it idle with that fluid in it..When I remove the transmission lines should I be prepared for a huge amount of fluid coming out?

 

Hmm, I wonder if compressed air can be used to push out the fluid or if that could harm the pump or other systems? If it works it would remove virtually all fluid before installing the new Mercon V.

 

You'll never get compressed air into all the places in the transmission where ATF hides. In my not so objective opinion the flush procedure (Flush) will get more out.

 

Oh yes I agree the flush should be done. I was inquiring about using the compressed air only after the flush was done, just to get most of the fluid used to do the flushing out of there.

 

I don't think it will help, but I also don't think it will hurt.