It's always best to check the manual. If you don't have one, any Yanmar dealer can tell you what to use. Some engines use the same oil in the engine and in the gearbox. Some use motor oil in the engine and transmission fluid in the gearbox. My 3GMf (20hp) uses 15-40 in the engine and in the gearbox.
Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR On Wed, Oct 22, 2025 at 5:52 PM James Hesketh via CnC-List < [email protected]> wrote: > Josh, > > Thank you for this comprehensive answer -- very helpful. > > I guess the containers I had on board were mislabeled as far as the oil > weight. W 20 would have been way too thin and I know that's not what was in > them (original labels missing, these were hand written with magic marker). > Glad I asked before searching and buying the same. And from now on I will > consult the manual before assuming something as important as lubrication > specs. :-) > > I'm on the right path. Appreciate your input. > > Jim > > Josh wrote: > >> Have you checked the owners manual? An internet search produced these >> links to a manual. >> >> https://www.manualslib.com/manual/927945/Yanmar-Ysb8.html >> <https://urldefense.com/v3/__https://www.manualslib.com/manual/927945/Yanmar-Ysb8.html__;!!LIr3w8kk_Xxm!t4RdicK7pF1TWIMi9l-x7a0Si6EmLtn0CUhItPT2HpQEOXMQxJFgcSr8NdTVTPIVg59IRmHE6aXW8isltSYXGmg$> >> >> >> https://forums.sailboatowners.com/attachments/yanmar_sb8_manual-pdf.216306/ >> <https://urldefense.com/v3/__https://forums.sailboatowners.com/attachments/yanmar_sb8_manual-pdf.216306/__;!!LIr3w8kk_Xxm!t4RdicK7pF1TWIMi9l-x7a0Si6EmLtn0CUhItPT2HpQEOXMQxJFgcSr8NdTVTPIVg59IRmHE6aXW8isl7mN62zo$> >> >> The chart will help you select the best oil. >> >> You should chose the oil based on the highest air temp which you expect >> to operate in since you're unlikely to change the oil as the seasons >> change. I expect that for most US that would be 20-35°C(68-95°F) - Unless >> you are very far north and never expect to operate on a 68°F day that puts >> you using SAE 30. This is great news since as you've already found SAE 20 >> is difficult to find. >> >> Shell Rotella T1 is a highly respected oil and readily available. Based >> on the information in the manual the engine and gearbox take the same oil >> which is also nice since you won't have to keep multiple different products. >> >> I'm a fan of Amsoil products. Their tech support is phenomenal. I've >> had great success calling them for product recommendations when nothing >> else seems to fit the bill. >> >> A quick refresher in oil tech: 5w-30 = 5 winter weight and 30 straight >> weight. 5 means that the oil moves like an SAE 5 at winter temps. Once >> the oil is up to temp the oil moves like an SAE 30. They do this for quick >> lubrication on startup. It is done be incorporating polymers that "coil >> up" in cold temps and uncoil/get stringy at hot temps. But what it also >> means is that the oil is built from a lower viscosity (near SAE 5) then add >> the polymers. And the first thing to break down and burn up is the >> additives so the oil will slowly move from SAE 30 at operating temp to SAE >> 5 at operating temp as the oil gets old. >> >> This is both a reason for and against using multi-grade oils in various >> applications. >> >> >> All the best, >> >> Josh Muckley >> S/V Sea Hawk >> 1989 C&C 37+ >> Solomons, MD >> >> Oct 20, 2025 14:16:53 James Hesketh via CnC-List <[email protected]>: >> >> When I got my boat with a Yanmar SB8 there were a couple quarts of 20w >> oil for the gearbox onboard, which I've used. >> >> Now I'm looking to purchase more and the only straight 20W I find (on >> Amazon) is a "Bearing Assembly Oil." >> >> Is that what I need, or what do people recommend for these old >> gearboxes? >> >> TIA >> Jim Hesketh >> "Whisper" C&C 26 >> >> Your contributions help pay the fees associated with this list and help >> to keep it active. Please help by making a small contribution using PayPal >> at: https://www.paypal.com/paypalme/stumurray >> <https://urldefense.com/v3/__https://www.paypal.com/paypalme/stumurray__;!!LIr3w8kk_Xxm!t4RdicK7pF1TWIMi9l-x7a0Si6EmLtn0CUhItPT2HpQEOXMQxJFgcSr8NdTVTPIVg59IRmHE6aXW8islwKWy5iw$> >> All contributions are greatly appreciated. > > Your contributions help pay the fees associated with this list and help to > keep it active. Please help by making a small contribution using PayPal > at: > https://urldefense.com/v3/__https://www.paypal.com/paypalme/stumurray__;!!LIr3w8kk_Xxm!t4RdicK7pF1TWIMi9l-x7a0Si6EmLtn0CUhItPT2HpQEOXMQxJFgcSr8NdTVTPIVg59IRmHE6aXW8islwKWy5iw$ > All contributions are greatly appreciated.
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