mine says it in the smaller engine manual that came with the boat. In the fluid specifications section. Is specifically says "Crankcase Oil (With Filter)"

year and boat might help get your some info.

 

Buy a gallon container and an extra quart. You may not need that extra quart, but you can keep it on board. I *think* you'll use right around 4 quarts.

 

Mine are 1996 4.3 LX's and use 5 quarts - that puts the level just a hair under the full mark. I have the remote oil filters so that may change my capacity some.

 

I have a 2001 4.3 it takes 5 Quarts.

 

I took the liberty of looking at some of your other post to see your have a 1991 220 DA - your welcome!

Link to mercruiser V6 1983-93 - note this is a huge file

According to the manual above on page 1B-4 you motor takes 4.5 quarts with filter.