My BIL has wrenched all his life. He told me about a technique for changing the trans fluid that you people might be interested in.

He says he drops the pan, cleans, installs new filter, etc., just like the usual routine. But to empty the torque converter, he detaches one of the lines to the trans cooler and has a helper hold it in a bucket or gallon jug. He turns the engine on - for just long enough for the trans pump to fill the jug - then shuts it down. We're talking SECONDS here...there is a lot of pressure in that trans pump. And if you don't have help to hold the line, you'll be squirting fluid all over the room - there is like 100 PSI on that line.

Anyway, he pumps out a gallon in seconds, shuts down, adds a gallon, and repeats until he reaches the total capacity of the trans. He's done pretty quick without wasting ANY fluid. There is very little mixing of new and old fluid because the fluid goes from the TC to the cooler and the return line from the cooler goes back to the trans sump. You get a couple ounces of mix...but nothing like the quarts of mix you get the other way...by repeatedly dropping the pan or sucking it out the dipstick tube.

Also, he installs a "drain bolt" in the pan, too. It's a bolt with a drain bolt in the center.

This makes a lot of sense to me. Comments welcome.

 

I thought tranny psi was closer to 10, no?

 

Could be...I know nothing about automatic transmissions other than routine maintenance.