I need to change out ATF fluid in both our 240 and 740 Volvos. The Bentley manuals says to disconnect the rear most Union ATF return line and then you do the rest of the procedure - you guys know that part. Bentley has the draining of the pan as a separate task. But the Haynes manual says to first drain the pan; then put the plug back in (both our cars have drain plugs); then remove the union and then do the rest of the procedure.

So, why does Bentley avoid draining, via, the plug first? Or why does Haynes include it as all part of the same procedure. Is there a safety to leaving the fluid in the pan and going directly to the union return line for draining?

Thanks -- diyer