I spoke with Yanmar about this issue a couple years ago. The Yanmar tech sent me a screen shot of the service manual. I can't figure out how to do a link here and can't past the screen shot, but this is the info:
Service Categories Use an engine oil the meets or exceeds the following guidelines and classifications: * API Service Categories CD, CF, CF-4, CI, and CI-4. * SAE Viscosity: 10W-30, 15W-40. Engine oil 10W-30 and 15W-40 can be used throughout the year. NOTICE * Be sure... * Change the oil... * Select the viscosity based on the ambient temperature where the engine is operated. See the SAE Service Grade Viscosity Chart (Figure 5). * Yanmar does not recommend the use of engine oil "additives". The Yanmar tech did not think there was any benefit to using synthetic oil. I use 15W-40 Rotella T4 in Michigan. Ambient temps during my May through September sailing season are 50 degrees to 80 degrees. Works fine, as far as I can tell. Jeff Laman 81 C&C34 Harmony (3GM -- 20hp) Ludington, MI ________________________________ From: dwight veinot via CnC-List <cnc-list@cnc-list.com> Sent: Monday, September 26, 2022 4:15 PM To: Stus-List <cnc-list@cnc-list.com> Cc: dwight veinot <dwight...@gmail.com> Subject: Stus-List Re: Rotella T5 - 10w30 vs 15w40? Yes Rotella is good oil. I use in 5W-40 T6 synthetic my diesel truck and it would be good for your Yanmar but it's expensive. For sailboat engines which hardly ever run in freezing temps SAE 30 would be fine. Basically all lubricating oils nowadays will do. In my Universal M4-30 I used 10w-40 or 15w-40 no special name. On Mon, Sep 26, 2022 at 5:05 PM Bill Coleman via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: My Yanmar 4JH3 calls for 15-40. I think most use this, Rotella. Bill Coleman On Mon, Sep 26, 2022 at 3:51 PM Dave S via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: Does it matter in any practical sense whether I use 10W-30, which is available, versus 15 W 40, which was available last time I bought a jug… Yanmar 2GM…. Thx. Dave. Sent from my iPhone -- Sent from Gmail Mobile
