Re: Changing the Oil Pan 5.7 Mercruiser
What's the year of the engine? Do you have a Mercruiser serial number for it (would be on a black tag above the starter on the block).
Depending on the year, the rear main seal may be a 2 piece job ('85 and older) that you replace by removing the rear main bearing cap (pan needs to be off). An '86 and newer engine has a 1 piece rear main seal that can be replaced without removing the pan. The front crank seal can be replaced on all years with out removing the oil pan.
If you have the engine out of the boat, there's no reason not to replace these seals since you would have easy access to them, and they're dirt cheap.
Using an auto oil pan depends on what's installed on the engine now. If your oil pan has the dipstick tube as part of it, you are not going to find an automotive equivalent. If the stick is separate (goes into a boss on the block), you may be able to use an automotive pan as long as you get the right year pan. Engines up to 1980 had the dipstick on the right side of the engine (while facing the engine). Then after that, engines had the dipstick on the left side of the engine. In '86 they started using the 1 piece rear main seal which requires a different pan.
There's no such thing as a marine oil pump. A standard small block Chevy pump will work fine. Make sure you get a new pick-up tube for the pump, and it's not a bad idea to have it tack welded to the side of the pump body (after setting the pickup tube to the proper height in the pan) so it doesn't drop off from vibration.
