I have a 502 mpi mag. It seems like it doesnt matter if i drive it hard or not it uses oil BUT i notice it more when the water is really rough vs smooth water. Its not uncommon for me to go through a qt to qt and a half in a weekend. I do boat alot but is this normal? Thanks for all your help guys!

It is not uncommon for a 502MPI to use a qt every 10hrs or so. I switched to Mobil 1 15-50 and it reduced my oil consumption by about 50%.

my 502's dont eat any oil but i have friends that use a qt during a hard poker run. i run valvoline vr1 20-50 racing oil and it seems to be pretty good with low oil temps and good oil pressures. it stays very consistant. the down side its like 8 bucks a qt.

Yep,
502 MPIs are known to use oil, not burn , just use it.
Dean

it is a function of the ultra light ring tensions they used to make power. if it annoys you you can replace them with the set that total seal makes specifically for that motor that fixes the problem completely.

When i bought the boat in March the guy had been using Castrol 20-50 so i continued using the same oil. This past weekend i put 7 hrs on it and it used a quart and a half?????

What oil filters are you running??? Do they have anti-drainback valves???

I would switch to better oil also.

Im running Mercruiser Oil Filters and i have plans on switching the oil over after i figure out what im going to do with the motor this winter. Whats the best oil?

Mobile 1 15w-50 pretty much solved my 502 oil consumption problems. I still keep a couple extra qts in the boat but hardly ever have to top off between oil changes any more.

I use either Mobile 1 or K&N oil filters (large ones)

Your 502 mpi oil consumption sounds about on par with mine. After a couple good weekends of boating Im about 1qt low.