My Haynes repair manual describes changing the transmission fluid and filter by dropping the transmission pan. It then says to re-install the pan and fill with 4 quarts of transmission fluid, start the engine and move through all gear ranges and back to park. It says to check the fluid level and add more if needed. I figure I might only need 4-5 quarts of new fluid even though the 4R70W transmission specs 13.9 quarts.

I assume Ford filled the transmission with Motorcraft Mercon V fluid at the factory (or whatever brand the factory uses).

Is it ok for me to mix 4 or 5 quarts of Amsoil or Castrol Mercon V transmission fluid with the 9 or 10 quarts of factory installed transmission fluid?

 

Hello temp1,

If you are just dropping the pan and changing the filter you are not draining all the transmission fluid. You don't have to drain all the fluid that's why your Haynes manual says "fill with 4 quarts", draining all the fluid is called a transmission flush. The torque converter holds most of the fluid and it also must be drained to do a whole flush. As far as fluid type look on the dip stick it will tell you what type of fluid your transmission has, if it says "Mercon V", it is synthetic, if it just says "Mercon" it is non-synthetic. I would not mix fluid types.

 

Thanks RK.

The dipstick does say Mercon V. I plan on putting in AMSOIL ATF fluid and I think I was told that it would be ok to mix it with other BRANDS of Mercon V transmission fluid.