[grommett]

Can car engine oil be used in a Magnum 350? I just need a small top-up and I bet car oil is cheaper than boat oil!

[WetWilly]

Answer - yes, and keep the rest of the bottle for future top-ups.

This is what Mercruiser has to say :

To help obtain optimum engine performance and to provide
maximum protection, we strongly recommend the use of Quicksilver
4-Cycle 25W-40 Marine Engine Oil. This oil is a special blend of
25-weight and 40-weight oils for marine engines. If not available, a
good grade, straight weight, detergent automotive oil of correct
viscosity, with an API classification of SH, CF/CF-2, may be used.
In those areas where Quicksilver 4-Cycle 25W-40 Marine Engine Oil
or a recommended straight weight oil are not available, a
multi-viscosity 20W-40 or, as a second but less preferable choice,
20W-50, with API service ratings of SH, CF/CF-2 may be used.
.and keep the rest of the bottle for future top-ups.

[ShabahZ280]

Use Marine Oil, and use Don't chance it. The engine is the most expensive and most crucial part of your boat. The price difference between marine oil and automotive oil will be worth it if you don't use the right stuff and end up ruining your engine. Price an engine recently?


This is from the Mercruiser Website.
MerCruiser Frequently Asked Questions:

What type of engine oil should I use? Can I use synthetic oil?

To help obtain optimum engine performance and to provide maximum protection, we strongly recommend the use of the following oils listed in the order of recommendation:

MerCruiser / Quicksilver Synthetic Blend, NMMA FC-W rated, 4 cycle oil.
MerCruiser / Quicksilver 25W40 NMMA FC-W rated oil.
A NMMA FC-W rated oil.
MerCruiser / Quicksilver 4-cycle 25W40, non FC-W rated oil.
A good grade straight weight detergent automotive oil per the operating chart below.

NOTE: The use of non-detergent oils, multi-viscosity oils (other than as specified), non-FC-W rated synthetic oils, low quality oils or oils that contain solid additives are specifically not recommended.

[WetWilly]

Sorry guys, I should have clarified my post to say that this was only a temporary measure to bring the oil level back up.

For the oil you run in your Mercruiser motor and for when you do your oil changes, I agree 100 percent with ShabahZ250! Use the recommended oil, anything else could have serious consequences down the road and unless you're need to run at WOT all the time or you have a highly modified motor, the OEM recommended oil is just fine.

But in the event the existing oil level in your motor is a "TAD" low (lets say just below the line on the dip stick), and the proper oil isn't available, alternative oils can be used, as stated in the Mercruiser manual.

Now if you find yourself "topping-up" a lot, time to see a mechanic cause you're probably burning oil and polluting the water...

Like they say; "Pay now or Pay later"!

WetWilly