Oil Question

[zad0030]

In our 350 Mag mpi we have been running 25w-40 becuase thats what our dealer has been giving us. Its the Mercruiser brand and I havnt noticed any problems with it.

Can someone with a similiar engine tell me what oil they are running.

[Jason B]

that's exaclty whaa my dealer gave me and what the merc site recommends

[chpthril]

Zad, I know this doesn't answer your ??? because I have the MP not Merc. Just wanted to share my thoughts on the whole oil debate

What are you looking for exactly? Since these engines are all marinized GM blocks, I'll bet that they all have about the same tolerances as far as oil pressure specs, bearing clearance, etc. The main thing, IMO, is to use a quality marine grade (*) oil in the proper weight for the temp range that the engine will be used in. Straight 40 seems to be an almost universal weight for marine engines, so you cant go wrong with that. If you are going to be using the boat from early spring on into fall, like us, a multi weight, like you have been using, gives you a lighter viscosity for better pump-ability when the engine temp is cold.

* Automotive grade oil is fine to use. The main diff between the 2 is the amount of moisture and rust inhibitors in the marine oil will better suspend (not allow to mix) water/condensation commonly found in the marine environment. Auto engines run much hotter then boats, so they have the ability to boil off condensation better then boat engines. If you are going to use an automotive oil, I'd recommend changing the oil more often.

[zad0030]

Thanks guys!

[R&T Babich]

Automotive grade oil is fine to use. The main diff between the 2 is the amount of moisture and rust inhibitors in the marine oil will better suspend (not allow to mix) water/condensation commonly found in the marine environment. Auto engines run much hotter then boats, so they have the ability to boil off condensation better then boat engines. If you are going to use an automotive oil, I'd recommend changing the oil more often.

chpthril - I agree with everything. Another thing to consider is how long the boat is in the marine environment. Our boat (350 Mag MPI) is on the water 50-60 hrs a year. Other boats are on the water all year (lucky ones). An auto in Seattle probably sees 100 times more marine environment than our boat. I change the oil every 6 months figuring that's long enough for it to be open to the atmosphere.