Oil weight for 3GM-30 in Baja

[Aussie_Sequoia]

Hi all,

Changing the oil in my Yanmar 3GM 30HP. I believe that there was SAE 40 in there before, but I have a spare 5 liters of SAE 50 on board.

We're cruising the Sea of Cortez... any idea if this is suitable for that engine coming up to Summer time and lots of hot days?

Cheers!

[Noname]

Yanmar recommends 30w for the 3gm30. 30w, 40w, and 50w all are very close in viscosity at operating temperature after the engine is warmed. They are not close in viscosity at cold temperatures such as 70-80F. The only problem with using the 50w oil will be not getting quite enough lubrication during the warm-up period for the engine. After warm-up, the lubrication should be OK. I assume you are talking about 50w and not 10w-50, which is quite different. Considering the price of oil versus the price of engine rebuilds, if it were my engine, I would buy some 30w and perhaps use the 50w for topping up the motor oil when needed.

[Aussie_Sequoia]

It will be over 100F during the next many months here... and I'll change the oil before it cools off anyway. Cheers for the info though

[Dockhead]

Originally Posted by Aussie_Sequoia

It will be over 100F during the next many months here... and I'll change the oil before it cools off anyway. Cheers for the info though

Yeah, but what is the water temperature? Marine diesels are typically very well cooled, and will maintain the same operating temp regardless of the ambient temperature. I would never deviate that far from the manufacturer's standard, personally, or in fact, at all. 50w (which I've never seen in my life; maybe you're talking about 20-50w?) would be practically like gear oil. I don't think it could be good.

Beware that semi-synthetic oil or oil of a higher grade than recommended can damage a marine engine. If I were you, I would stick to exactly what Yanmar recommends. Here's a good article: Oil for yacht engines

[Noname]

Hope all goes well with the sae50w. Good cruisin' to ya.