Best Oil For Old OMC

[Gary H NC]

I was wondering what oil the other members are running.
I have an 87 4.3 OMC and the book calls for SAE 30.
A marine mechanic i know said to use 25w 50...
The engine has a good bit of hours on it but runs smooth and doesn't use oil.
The last time i changed the oil was the first time i done it myself.
I noticed my oil pressure is less now with the straight 30,
I'm thinking the shop must have had the thicker oil in it before.

 

[Chris1956]

Re: Best Oil For Old OMC

Gary, I have a Mercruiser 4.3LX Alpha and use my boat in the winter, until the fish leave in Late Nov or Dec. I therefore use the Mercruiser multi-weight oil (25W-40), since I feel it is a bit thinner in the cold months, for starting. I would recommend the same, if you boat in cold weather. If not, you could use SAE 40 oil, for extra protection, above the SAE 30.

PS - the automotive multi-vis oil is a different formulation than the Mercruiser multi-vis. I know it is not recommended by Mercury.

 

[Gary H NC]

Re: Best Oil For Old OMC

Thanks Chris, I think the 25w-40 must have been what was in there before.
That would still be thicker than the 30W.?
I only use the boat in warm weather so i think i will switch to the 25W-40 and give it a try..

 

[Chris1956]

Re: Best Oil For Old OMC

Gary, if the temp is warm, the 25W-40 will be thicker than the SAE 30 oil. When the weather is cold, the 25W-40 oil will be thinner than the SAE 30 Oil. The big "W" stands for "winter" in a multi-viscosity oil. The "w" in the straight weight oil stands for "weight", not winter, as a straight weight oil will thicken as the temperature decreases. The multi-viscosity oil actually thins as the temp drops.