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://forums.sailboatowners.com/attachments/yanmar_sb8_manual-pdf.216306/ > > 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 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://www.paypal.com/paypalme/stumurray All contributions are greatly appreciated.
