I searched threads for this answer, but have to embarrass myself by asking anyway: Gen 6 502 magnum-- when changing oil I have the drain pan plug hose attached and I warm up the engine, pull the hose through the boat drain plug hole and let it drain for 24 hours-- at that time it is not draining any more. I raise the boat trailer as far as possible to drain any remaining oil-- then lower the trailer as far as possible as well. Then when refilling-- it only takes 4.5 to 5 quarts to come to the dipstick full mark. The Clymer Mercruiser manual specs 9 quart capacity for the 502 magnum. What am I doing wrong to not get out more oil? That seems a lot of oil left in there...

I have a 454 but im pretty sure they hold same amout of oil, my sucks up throught dipstick with electric drill pump, anyways you still have oil in the lines and filter so run it for 10 min and then check if it need another quart, but 5-6 it is around what mine takes, but im suckjing through dip stick so there could be a little oil below that in pan

I put a hose adaptor on the end of my whip "oil drain hose" And then used a pump to suck the oil out through the hose with fitting on the end. "not through dipstick' I think sucking out is better than letting it drain on its own. personal prefrence.

I bought a pump that is mounted on a plastic bucket, pumps out in a minute or so. I have the drain adapter hose kits also, makes it an easy and neat job.
I find the same problem when filling, they never take 8 quarts. I even start it and let it warm up, turn it off and check the levels. The same when the boat is in the water. Both are full, got me on that one too. Maybe someone else knows.
BC

When your changing the oil are you removing the old filter? the filter holds a quart by itself.

They have an 8 qt capacity with a filter change. It should take 6.5-7 quarts to hit the full mark until you fire the engine and then it will need another quart or so. You can't get every drop out, but I have the same drain hoses as you and I use 15 qts for 2 engines.

the merc spec is for an empty motor. i just had my 502's rebuilt and they took 9 qts of oil each. the 3 oil lines, oil cooler, filter, etc. hold the rest of the oil.