Marine oil VS Standard Synthetics

[cjarrett]

I have been looking for some boating forums with a good number of members to help me learn more about what oil I should be using in my engines. I can't seem to find any definitive answers to what additives are used in marine oils that make them a better choice.

I have twin 2008 VP 4.3 OSI-JF engines. Have been using Sierra synthetic blend 25w-40 for the last year. We bought the boat in 2020 with around 1,000hrs on it.

Id rather use a full synthetic but can't find a marine grade oil in the weights that Volvo now recommends. They used to recommend 30W full synthetic but now recommend a 10W-40 synthetic.

Any suggestions or information you can help with? I'd love to learn more. I've also searched and nothing came up here in the first 4 pages of results.
Thanks!

 

[dingbat]

What type of oil and lube to use

I don't think you can go wrong using either Rotella or Delo in the 15/40 viscosity range.

forums.iboats.com

 

[QBhoy]

You could use the quicksilver synthetic blend 25w40 that mercruiser use in the identical in every way, engine. The 4.3 mpi gm.
Not sure where you are in the world, but here in the U.K…there isn’t (in my opinion) a better marine oil than the rock oil stuff. That’s either 10w40 or 15w40 spec for this engine of yours.
I use rock oil in my 2016 merc outboard. Always used the quicksilver synthetic blend in my mercruiser v8 mpi (same as the VP gxi and osi), but going to switch to rock oil I think. Only stayed quicksilver to keep the service file OEM. But it’s nowhere near as good an oil as the former

 

[paulswagelock]

There will be no advantage to a full synthetic for your application. More important is the correct viscosity and an applicable additive pack. Stop overthinking this. Keep using what you were, it is fine, or switch to a quality 15w40 diesel rated oil, not an API rated one.

 

[QBhoy]

There will be no advantage to a full synthetic for your application. More important is the correct viscosity and an applicable additive pack. Stop overthinking this. Keep using what you were, it is fine, or switch to a quality 15w40 diesel rated oil, not an API rated one.

Tend to agree partly with this. I don’t think I’d go fully synthetic on an engine that’s essentially been around for decades and decades…doing just fine on mineral or semi all the while. These aren’t high tolerance state of the art and finely built things. Amazing as they are..solid as they are…they are crudely built old school things. The reality is that any old oil will likely not harm these things. Can’t think of there ever being an occasion when an engine like this was ever damaged with the wrong type of oil in it. Not that I recommend such a thing. But just to make a point. 25w40, 10w40 or 15w40 would be just spot on, for most circumstances. Good to use a marine oil, I personally think, though.

 

[Lou C]

The actual advantages with a full syn would be in temperature extremes of cold and heat, most likely the cold is not a factor in marine use, however, heat can be, as far as oil temp. However, if you look at what Merc recommends the most they will recommend is their Syn Blend 25/40 which is the same as what you are already using. So unless you have high oil temp readings I think what you are using is fine.
In the past I have seen Amsoil marketing a straight 30 and 10w/40 syn (maybe they make it for Volvo?) but if you got 1000 hrs of good use on what was used I'd keep using that.

 

[tpenfield]

I'm not much of an oil connoisseur, I just go with the recommended weight in any brand. Most oils meet the relevant spec's, unless you really dig deep into the bargain aisle.

 

[Scott06]

Agree don‘t over think it. i dont think in that application (stock 4.3) you really take advantage of synthetics. Any of the mercury 25-50 or 25-50 marine oils are fine, 15-40 rotella works great. Also have used mobil one 15-40 and 15-50. you’re only putting what 75 hrs a year on it ? any decent quality 40 weight or so will be just fine.

 

[Scott Danforth]

oooh......another oil thread.

 

[racerone]

Fact-----A spinning shaft wants to stay where it is.------So in a boat in rough seas the crankshaft and flywheel want to stay put.-----But boat with engine attached want the crankshaft to move with it.------Make sure you use the correct oil.

 

[cjarrett]

Appreciate all the info. I had been searching for 'marine oil' related searches to understand the additives or differences in marine oil but have found it hard to get good info.

This is all helpful though. Likely will stick with either a blended or full synth 15w-40. I don't mind paying a little extra for oil once a year, boats aren't cheap so a little added protection is good peace of mind. I boated in both 0deg C and 45deg C weather this year in Vancouver, so the boat sees a pretty good range.
Taken yesterday when I popped down to check on the boat.