Multigrade Oil in Yanmar 1GM Engine ?

[troppo]

The Yanmar manual I checked said use monograde oil SAE 30 or 40 in 1GM engine, so did the Caltex "find oil" web page.

But one maintenance sheet I saw said multigrade 15W40 and some other references I can't find now said the same.

Is it okay to use multigrade 15W40 in the 1GM engine or best to stick with monograde?

I confess I have used multigrade oil in my 4 stroke lawn mowers for decades though the manuals say monograde, and the engines outlasted the other components. I used it as I am totally lazy and cheap and reasonable quality multigrade was easier and cheaper to buy in bulk than the hard-to-find expensive small bottles of monograde oil that were only stocked in the specialist mower shop.

[daddle]

Do what the actual manual says. The engineers thought about it. They may know something we do not.

[Chief Engineer]

Rotella 30 weight and 15-40 are the same price here.

[djmarchand]

When Yanmar wrote that manual about 30 years ago, multigrade oils were somewhat new and didn't have as much lubricity as single grade oils. That is still the case (except for synthetics) but the gap has narrowed considerably. You can use either straight 30 wt or 15-40 multigrade. Newer Yanmar engines specify either.

[Inlet Marine Services]

Yanmar sell 2 oil a 30w and a 15/40. Depending on your location in the world, if the temp is warm and stays that way use 30w. If the temp swings from cold to hot use a 15/40

[motion30]

I have a 1973 lehman 120 I was using 30w per the manual On my first ICW trip running 9-11hrs a day I used a about a quart of oil every 2-3 days After changing to 15-40 same brand oil (rotella) I used one quart every 50 hrs I am no expert but that is my experience

[Inlet Marine Services]

Lehman engine is a different story, 30w only no multi weight oil. You will have oil pressure fluctions.