I read Kovalsky's article on this site with suggestions for ATF change and have a few questions for others who might be more expert than I. I obviously want this to be a preventative
maintenance rather than doing more harm than good; I'm capable as a DIYer, but by no means a pro. Cost is a big factor for me, so I'd like to do this myself.

My motorhome has sat the last 3 years. It has 130,000 miles, and this transmission seems to be extremely well-engineered including how cool it runs no matter how hot the environment. In fact, many times I have towed a boat through desert in the summer and kept tabs on how hot the trans cooler and the engine temp was.

The fluid still appears new now, although it has about 40,000 tough miles (maybe more) and perhaps 8 years on it. At the last change done at a trans shop, the pan and magnet were clean as was the filter when they pulled it. They only changed the filter and the fluid in the pan. After looking for it, I'm surprised to notice it does not have a drain plug in the transmission pan!

I'm about to put it into service to tow a trailer from Southern California to Michigan, so I want to change the fluid. I have done a similar service that Kovalsky wrote about on my 1999 RX300 (like a Camry wagon or Toyota Highlander). But it was suggested to me that I might possibly introduce air into the valve body and this might be harmful to the motorhome.

Because there are currently no leaks, the condition was good last service, and I read there is issue with the A4OD's filter fitment that a non-experienced DIY like me might have a problem with, I'm leaning towards fluid exchange via the cooler return line without dropping the pan. So here are my questions:

1. Are there reasons not to change fluid by pumping out old fluid through the cooler line? Air in valve body, etc.? Can I damage the transmission by using the transmission to pump out fluid?

2. Does anyone who has performed this method have any additional suggestions before I start?

3. Since Kovalsky mentioned it requires 5 gallons of ATF, suggestions for the most cost-effective way or source to purchase?

Any and all suggestions are appreciated. Thank you.

 

There is no way to damage the transmission IF you follow the procedure. The only risk is if you leave the engine running after the pan is empty, which is indicated by air instead of fluid coming out of the hose.

Air in the valve body is a non-issue.

There is really no reason to replace the filter every time the fluid is changed. If there is enough junk that the filter needs to be replaced the transmission is junk.

 

Thanks for all your information Mark. I had a friend help to be the starter, and all went smoothly. We exchanged one gallon at a time. As I previously reported, the fluid appeared to be in pink condition on the dipstick, but in the clear tube I could see the old fluid was darker, not burned or really dark, but not in "good" condition. I think this was a worthwhile endeavor and I thank you for your advice.
When shopping for "Mercon" fluid, I found a confusing assortment of choices. I assumed any brand/product that claimed Mercon compatibility must be compatible to be mixed with each other, since it's nearly impossible to purge the entire system anyway.
I shopped at Napa, Autozone, Pep Boys, but I ended up at Walmart while getting groceries. They had the same choices, including the Valvoline product designed for vehicles with more than 75,000 miles. I wondered if I really wanted the additives in the Valvoline high mileage product since my transmission has no problems at all, and I'd like to keep it that way (forever?). However, it appeared like a good product so I bought it, but they only had 3 gallons, and I assumed if it truly is compatible with Mercon I could mix with two gallons of cheaper generic Dex/Merc fluid. I hope I was not wrong!
After completing the service, I read the Valvoline high mileage bottle more thourghly, and saw it claims also to be compatible with Toyota T-IV, which I've always had to buy a specifically different fluid and was warned by the Lexus mechanic about fluid non-compatibility after they, at their suggestion, replaced my transmission under warrantee with an updated unit at 70,000 miles. Now I'm not so sure about how it can claim to be compatible with Mercon AND T-IV. Any ideas? Am I putting something in the Ford I will regret later? OR, is this Valvoline mixture really a superior product?

 

It will be fine.