Oil for rebuilt Mercruiser 228

[Durango318]

We just became the owners of a 1979 43' Delta Clipper. She has twin rebuilt Mercruiser 228's tied to Velvet drives.
The engines have about 300 hours since the rebuild. They are raw water cooled and run about 140 degrees and oil pressure's at 40 psi at 2000 rpm with 5W-30 Valvoline. I wanted to use a more traditional marine Merc oil like 25W-40 but I have no idea what oil pump or bearing clearances were used in the rebuild and don't want something to pop with the thicker oil.
I asked the former owner why the 5-30 and he said he wanted the get the oil throughout the engine quickly when started and he didn't want the oil pressure too high. The boat is in the California delta and the engine compartment will likely never see less than 40 degrees. My son suggested Valvoline 15W-40 Diesel engine oil.

Any Ideas ?

 

[agallant80]

Re: Oil for rebuilt Mercruiser 228

Iuse mobile 1 15-40. I think according to merc as long as its 40 weight you are good. They have changed the specs several times over the years.

 

[alldodge]

Re: Oil for rebuilt Mercruiser 228

Many here use the 15-40 diesel oil because of the added zinc or other reasons. As agallant mentioned so long as it is 40W you should be good. Merc indicates so long as you stay above 50 degrees you can use straight 40. I put the boat up if I have to wear a jacket so straight 40 is the way I go.

 

[Volphin]

Re: Oil for rebuilt Mercruiser 228

The Merc 25/40 won't hurt a thing. If you want to keep using the V, that's cool too. But I'd use the full synthetic Valvoline 5/30.

 

[OldNBold51]

Re: Oil for rebuilt Mercruiser 228

diesel oil is cheap, easy to find and has a great additive package that works well in boating applications. It's one of the top 5 choices.

Valvoline VR1 is a racing oil and has the additive package that works well with flat tappet engines.

Oil has been discussed 1000's of times. Most will agree that as long as you have oil in the engine and don't run WFO all the time, whatever you have in the engine should be OK. Most also will agree that it's not what oil you have in the engine, it's how clean and fresh the oil is that counts.