Old Question

[new_to_me]

I don’t mean to stir up and old question but it is kind of confusing with all the recommendations on oil from the different boat manufactures. I will always refer to my service manual for advice before moving forward with service. This year I sold my boat with a Merc 350 and bought one with a Volvo 350 catalyst. It is a 2011 5.7 300-P, DPS-A. I had the other boat for 3 years and used straight quicksilver 25w 40. I know that the oil for this new boat engine has some specific requirements because of the catalyst. The marina that has serviced this boat says they have always run the Merc 25w40 in it.
The confusion is my owner’s manual says to use Volvo oil first or a API SM and/or ILSAC GF-4 spec oil 5W30, 10W30, 10W40, 15W50 or straight 30W. It states NOT to use diesel oil or oil additives because of the catalyst. The work shop manual from Volvo states to NOT use multi viscosity oils, but approves the straight 30. Now the date code on the work shop manual is 2004 and makes no reference to the catalyst.
I have owned GM products most of my life and my o8 ¾ ton Chevy work van has the small 4.8 V-8 and gets run hard all day, I also have a 88 Chevy 4WD short box p/u that has a 350 in it with over 560,000 miles on the original engine. Both these engines are small block GM and have had nothing but multi viscosity oils using Castrol and Lucas products in them with no issues yet. My 05 Durmax has 220,000 with nothing but Amsoil 15w 40. I know these engines are not subject to high rpms as the boat will be. I am just looking to find out the difference between the two manuals and get the right oil wiyh out breaking the bank. Just shelled out a pretty penny for their drive oil. I know Volvo gets its oil from their oil plant next to their spark plug plant next to their grease plant and so on. Any help

 

[rideahorse]

I guess on a boat I wouldn't worry about the w rating. It looks like they want at least a 30w oil in it for warm weather. I have used diesel oil in all my new cars and have never had a problem with them. And I run everything to the grave and then resurrect them and run them to the grave again.

 

[fdcg27]

So just use an API SM or SN HD30.
You could certainly use a mutigrade of sufficient thickness, but as rideahorse noted, cold weather starts shouldn't be any concern with a boat.
You might also contact Volvo and ask them whether an API SN 10W-40 or 15W-50 would be okay to use. The cat shouldn't be any more prone to failure using these oils than the ones in your road vehicles and the engine doesn't know that it's installed in a boat.

 

[new_to_me]

Thanks for the help