Well, here is the difference, the trans picks up its fluid out of the pan and pumps it throughout the transmission, to the cooler and back into the pan for pick up. When you pump a gallon out of the fitting at the radiator and pour a gallon in at the dipstick tube what happens is you are continuously pouring in brand new fluid for it to suck up and all the while you are not letting the old nasty stuff to return to the pan. Now granted when you pour fresh type red fluid into the pan it mixes with the existing type brown fluid but after that first gallon or so the pan is pretty much evacuated of old nasty brown fluid and is now sucking up nothing but clean red fluid.

In your set up you would drain the old nasty out, pour in fresh red stuff, run it and mix everything up to an even mixture of mosty old nasty with a little new stuff and then drain it out and do it again. When you drain the AW3040 pain and refill it, it takes about 2.5 quarts (not that much). I'm saying it would take forever to get the fluid nice and red if you kept mixing the new with the old instead of chasing the old out with the new. AW5042 (850 trans) transmissions seem to be harder on fluid than any other trans that Volvo has put out and it routinely takes me about 4 gallons to get one to where it is pumping out fluid that looks just like what I am pouring in. The AW3040 on the other hand has been the best on fluid in my experience. I just finally did my own personal car awhile back because I felt bad! The 960's are a pain in the but though because they have a different size fitting and the clear vinyl hose that I use for everything else does not want to fit right so I had to make an adapter for it.


I know it was a bit long but I hope it answers your question and helps you out.

Mark