Traditionally Volvo has recommeded auto trans oil change every 20,000 miles. I know on the newer cars {850/70} there is no recommendation. But my experience {22 years exclusively Volvo} has proven the 20,000 miles to be a good interval.

Draining and refilling doesn't get the job done. A "flush" is required and it is relatively easy.

#1: Drain all oil from drain plug.

#2: Remove upper cooler line at radiator

#3: Attach appropriate size hose to end of line

#4: Run loose end of hose into clear jug or drain pan

#5: Add 4 qts. trans oil

#6: Start engine and add 3-4 qts. trans oil

as old trans oil drains into jug

#7: Shut off engine when 4 qts. has been flushed into jug

#8: Remove hose and reattach cooler line to radiator

#9: Top off trans oil level to full COLD mark