Friction modifiers and viscosity improvers are the additives found in modern "car" oil that you DONT want in a performance marine oil.

Car oils use a lightweight BASE oil (the 15 weight in a 15w40) and then put in "longchain viscosity improvers" to yield the 40 number. A marine application will "chop up" and "use up" the viscosity modifiers pretty quickly, leaving the base oil only (the 15w).

The friction improvers/modifiers are added to make up for the removal of zinc and phosphorus (both of which are counterproductive in zero-emissions goals). These also are a poor crutch vs the proven (but less green) zinc and phosphorus.

So what Merc does is to mix 25w and 40w base oils..

And outside of Merc oil, you have to understand the "secret language" of modern motor oils

All 5wXX and 0wXX oils are loaded with boat-unfriendly chemistry.

All 20wXX oils are considered NON MAINSTREAM AUTO/TRUCK products and can get away with giving more of what you want and less of what you don't need. Keep that in mind.

Any oil labeled MOTORCYCLE OIL will be free of friction modifiers because otherwise the wet clutches would slip like heck.

Any oil labeled LAWNCARE or UTILITY oil will have more zinc and phosphorus in em. Mower engines are a similar duty cycle as a marine engine. Mower engines typically run flat tappet cams, which require zinc.

Racing oils are a mixed bag. Some are labeled racing oil in order to allow them to use a formulation that is desirable for motors and undesirable for catalytic converters - while still containing decent detergent package and good corrosion control. Other racing oils are true racing oils that are low detergent and zero extended anti corrosion additives and are designed to be run hard and immediately changed - that's not what you want In a boat.

Sooooooo. There's more to it than you'd think on the surface.

20w40 motorcycle/marine/lawnmower oil is your friend.

Nothing wrong with a synthetic as long as it meets the discussion above..

Full synthetic motorcycle oil is great.
V Twin labeled Mobil 1 is fantastic stuff.

But honestly, lawnmower oil is best value.

I always use only synthetic oil in my boat, mostly Mobile 1 or Pennzoil Platinum, no problems, I see no reason not to use.

Would an oil that had both high levels of zinc and phosphorus with friction modifiers be a good thing?

if synthetic oil was so slick that lifter rollers won't spin on the cam I want that oil.
GM says synthetic oil in my ZO6 and its got roller lifters and my guess all of the GM trucks, and sport utilities that have roller lifters and last multiple hundredhundreds of thousands of miles and roller lifters and cams are not the issues.

it was something Bob Teague said many gazillion years ago so It had been hashed out back then. Look at this thread starts hundred years ago awesome.
okay, back to present day. Oil threads just won’t die. Mobil 1 15w-50 and vslvoline vr1 conv for the syn and conventional wins.

I had premature failure once,..........:D
https://cimg1.ibsrv.net/gimg/www.off...fb64ecafaa.jpg

https://drivenracingoil.com/i-304978...arine-oil.html


Loaded with ZDDP for added protection, MR50 offers an application specific product designed for this demanding performance environment. Driven's certified lubrication engineers have worked with marine engine builders to develop a first-in-class synthetic product that delivers performance and value. Excellent protection for high performance marine engines. Ideal for flat tappet cams, big blocks and blown marine engines. MR50 contains rust inhibitors for winter storage and defense against ethanol blended fuel. Viscosity typical of 15W-50.

Been using Driven oil this summer

What's your opinion on Mobil-1 15w-50 which is popular choice here. Label states it has added zinc.
https://www.mobil.com/en/lubricants/...obil-1-15w-50/

thanks

What Pismo10 said on sept 13th. Most any all will work fine.
Multi viscosity oils used to be an issue in marine engines decades ago, losing viscosity, but with standard service intervals, no longer an issue.

But they are taking more and more zinc out of most standard automotive type oils, so one with extra zinc would be good for flat tappet motors, the zinc may cause less wear on them after hundreds of hours.

Just FYI, another oil brand.

i have used this for 3 decades. Schaeffer brand. Their 15w40 diesel oil. Use in everything except new vehicles due to viscosity.

Schaeffer stated in the 1800's making grease for wagon wheels. Half the price of other high tech oils. It's a conventional oil, not synthetic. But it matches most all specs of a true synthetic so it must be pretty refined. Actually just went to the Racing oil version of the Supreme 7000. Exact same oil with more zinc since they are being forced to reduce the zinc these days in non-racing oils.

I've got a 11hp snapper mower 30 years old and the mower is falling apart but no oil usage and no smoke. Not bad.
But like Pismo10 said....