The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.
Since this topic drifted off to oil changes, I would like to hear thoughts on frequency ... have a 2015 Suzuki 9.9 (long shaft I *think*) and AFAIK only been in fresh H2O, interesting to hear about the custom flush fitting though. Super quiet mill, sometimes I forget it is running when using the tiller extension and sitting forward.
I have no records of oil changes, so don't know if synthetic has ever been used. I assume I could switch at next oil change though; don't know when last change was but I burned < 1 tank of fuel all season 2018, so wondering if oil change recommendation is based on # of revs, appearance of the oil, every season, etc. I know, I could always read the fine manual, but this group has more seagoing and lake-going experience and is tons more fun
I believe the general instructions for replacing oil is every 25 hrs of operation or annually....but I could be wrong regarding the hours. In any case, I perform oil changes annually....and sometimes I have procrastinated and let it go a bit beyond that to say 1 1 /2 years or so. I have a Honda 9.9 2006 and I never had ill effects from using the regular oil recommended which is not synthetic. No noticeable oil loss except the one time that I forgot to reinstall the dip stick and that was a bit of a mess but even then, when I installed the dipstick after returning to my marina from having the boat out for a week for re-applying anti-fouling paint at a marina across the river, the dip stick reading indicated about half way up the safe range and so I never added oil the whole season and the dipstick reading never changed.
I sail between 40-60 times a year and these are almost always day sailing with most use of the outboard for getting into and out of the marina 10 minutes or so going out and 10 minutes coming back in and then sometimes for 1/2-1 hour if the wind dies, etc. So, I estimate approximately 16-17 hrs of in and out of the marina and perhaps another 6-8 hours for when I have used the outboard longer on a sailing day.....this then being no more than 25-30 hrs tops annually. This is in river water and I do use the boat all year round, just much less during winter months. (I was out sailing about a week or so ago.)
My thought is that these outboards are much more forgiving regarding oil management compared to gas fuel. Almost all issues are regarding moisture in gas or how long the gas has been sitting around or in the fuel lines and carburetor of the outboard. Using Stabil or Startron helps mitigate issues with moisture in the gas tanks and draining or running out the fuel lines and carburetor of the outboard is also a good idea if not using the outboard for prolonged periods or infrequently such as for 3 weeks or more at a time. During winter months, I run the gas out of my outboard if I figure I may not be back on the boat for more than 2 weeks. Usually, I will be down at the marina every 2 weeks or more often to either sail or at least to start up the engine for 5-10 minutes to ensure no deposits dry up inside the fuel lines/internals of the outboard. During the Spring/Summer/Fall, I am usually on the boat or sailing frequently and so I then do not run the gas out of the outboard - Then I figure it is best to keep the outboard fuel lines and carburetor full of gas t minimize condensation/water forming inside and since outboard used frequently, no deposits with form on the internals.
The above approach has worked fine for me since 2006 but this past year, the outboard now 12-13 years old, it started t act up and cleaning out the internals did not work. But after the carburetor was replaced, the outboard is back to same as new again.
So....being concerned about your oil management is important but it is the gas management that so much more important. My opinion !
My new Tohatsu manual says to change the oil every 100 hours or 6 months. I doubt I come close to 100 hrs in my 6 month season. I change the oil using synthetic at the end of my 6 month season so as not to leave dirty contaminated oil in the engine over the winter that can attack metal.
Scott-"IMPULSE"87'C25/SR/WK/Din.#5688 Sailing out of Glen Cove,L.I Sound
Now that I think of it some more, reading your post, it is probably 100 hrs or annual for Hondas as well. I believe the first year it was 25 hrs. In either case for sailboats, generally we do not put that many hours on annually and so the annual requirement becomes the default and for many that means that after their sailing season which oftentimes is not a year-round, they change their oil at the end of the sailing season for the reason(s) Scott stated.
Notice: The advice given on this site is based upon individual or quoted experience, yours may differ. The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.