Honestly the oil you’re using is good but if you really want to try something different in a 40 then a simple choice, no matter how boring it sounds. I know we hate boring in here.
Why not the tried, true, tested, recommended oil of all time for marine engines?
Mercury Marine Quicksilver 25w40 oil is a straight weight 40, no viscosity agent/improver to break down and contains higher levels of anti corrosion agents
You can read the actual labels on Amazons site for both 25w40 products. Conventional and semi syn
https://www.amazon.com/QuickSilver-...0147492528&psc=1#immersive-view_1725363490405
Below is Mercs site but the labels above on Amazon link is more informative
Choice of conventional or semi syn
https://www.quicksilver-products.com/en/marine/marine-engine-oil/marine-engine-oil-4-stroke
My family and friends have been boating for decades, all types and sizes.
I’ll never forget the time many years ago for the first time ever my brother decided not to use Quicksilver 25/40 oil, he figured Castrol 20/50 should work just as good as even if it shears there is a safety being it’s 20/50 vs 25/40
The boat was a 28 SeaRay Sundance with twin v-6s was out in the ocean fishing then came back home through Jones Inlet to his waterfront home in Massapequa
He couldn’t believe it, back down to idle both engines were clattering like a piano keyboard without strings.
He dumped that oil and back to Quicksilver
I’m not a conformist but it’s a marine oil made for high stress applications, a boat has no wheels like a car does. The engines are literally pushing a log through water, the Merc oil won’t thin out and in a salt environment has the proper additives to prevent internal rust and corrosion. Think piston walls when boat isn’t in use.
I know many balk at the price but I look at it as a speciality oil, it’s to me not that badly priced
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