Re: 9.8hp tohatsu oil/speed
Rich,
At about p59 of the owner's manual, the oil level check is in the "daily inspection" table. Once you have been running the motor a while and know its oil consumption characteristics, you can probably check it weekly.
Somewhere around p65 of your owner's manual, the "periodic inspection" table shows that it is recommended to change oil at the first 20 hours, and then every 50 hours (or semi-annually) thereafter. I like to see the LU lube and crankcase oil changed shortly after break-in (about 10-20 hours), and then every 50 hours (or at least annually). The initial change will take out any factory machining debris. After that, it's just a matter of getting rid of the old, dirty oil.
One thing that can limit top speed is too much crankcase oil. If you are over full, even a drop, you will have issues, because of crankcase pressurization, (or if severely over full, liquid lock). On new motors, I fill the crankcase to 1/2 on the dipstick. After a solid break-in with lots of full throttle operation in warm weather, I typically fill to about 3/4 on the stick. Resist the temptation to dump in a whole quart bottle of oil, as you will be way over full. It only needs about 3/4 of a quart from empty -- but you must VERIFY the level on the dipstick. Also, on the MFS8/9.8, because the valve cover and cylinder head comprise a "shelf" at the back of the motor (especially if the motor is tilted way down), you may want to tilt the motor up for a minute or two after filling oil (and then return to vertical), so the oil gets into the sump, in order to get an accurate dipstick reading. Be sure that the dipstick is fully seated in the bore, because if it isn't, the stick will be too high, and you may get fooled into adding too much oil.
Keep in mind that all 4-stroke outboards of all brands will "make" some oil. (The level will rise with use). This is due to fuel residue/byproducts that made it past the rings and valve seats mixing with the oil. Because the oil sump runs very cool on outboards (being splashed with water frequently), the oil never gets hot enough to boil these contaminants out of the oil. The result is "making oil".
Outboards will "make" more oil:
1- If they are run slowly or idled a lot;
2- If they are new, and the rings have not fully seated;
3- If synthetic oil is used;
4- If the oil is too heavy.
The best oil for your MFS9.8A3 is non-synthetic, FC-W rated, SAE 10w-30, 4-stroke outboard oil.
