So I drained the ATF from my auto on Saturday. I was expecting it to just about fill my 10qt oil pan (specs say it drains about 8ish qts). The container I poured it in showed me that I only drained out about 3.5 qts. What's that about?

I am on an almost level surface. The driveway is about a 5% slope and I had the front on the uphill.

I put 3.5qt of redline back in it and the dipstick shows it's about in the right area. I didn't drop the pan and change whatever filter is in it, but that can't be too much more than one qt. tied up in the filter.

 

Anyone know what happened?

The listed capacity includes the torque converter, cooler lines, cooler, etc. You won't get it all out. The best way IMHO to flush a tranny is to disconnect the tranny cooler RETURN line at the tranny, connect a hose and put the end in a jug, then run the engine until a quart or two comes out, shut off the engine, empty the jug, replace the tranny fluid with the same amount of new that was in the jug, repeat until you have used at least the system capacity of new fluid. Not perfect but way better than just draining the pan and refilling.

That's the crazy part...

I swear the fluid book at the car parts store said it takes somewhere around 8qt on a simple "drain".... maybe that was a full R&R takes 8qt.... oh well.