Oil light warning on 9.8 motors

[BobGlover]

I’ve got several Tohatsu/Nissan 9.8 4 stroke motors. If I’m going full throttle, sometimes the motor will miss and the low oil light comes on. If I back off to idle, the oil light goes off & everything returns to normal. This occurs on my motors and a friends 9.8 Mercury (manufactured by Tohatsu). What causes this?

 

[pvanv]

If you over rev, the ESG will engage, and that will trigger the LED, as well as stagger the ignition to prevent you from exceeding 6250 RPM. (The max WOT RPM is supposed to be 6000 RPM). Also, if the oil is over full, running at high speeds can cause oil aeration, which can cause low oil pressure. You can test by installing a tachometer.

 

[pvanv]

Lokk on page 32 of your owners manual (depending on your specific model. That is for the MFS9.8A3. http://tohatsu.com/tech_info/own_man_pdfs/Toh_MFS8A3_98A3_003-11082-9.pdf

 

[BobGlover]

Thanks for the info. It may be oil overfilled, but probably the over rev limiter. I’ll check the oil levels just to be sure.

 

[ahicks]

Re: rev limiter thought, possibly too small a prop?

 

[Sea Rider]

Tohatsu portable outboards comes factory delivered with medium pitch props so near impossible for them to over rev not even powering light applications such as inflatable boats.

The 3 engines I currently run were found to be over propped when water tested on flat water cond, had to go per 1-2 less pitch props from factory delivered ones to rev close to max wot rpm range.

So, if still with factory delivered props it's surely something else aside from over revving...

Happy Boating

 

[BobGlover]

These motors aren’t run for hours at a time, so it’s possible they ‘make oil’. How long should they be run at one time to eliminate this?

 

[pvanv]

These motors aren’t run for hours at a time, so it’s possible they ‘make oil’. How long should they be run at one time to eliminate this?

It's not how long, it's HOW.
Hot and hard is what you want.
Cool waters, idling, synthetic oils, all contribute to making oil.

 

[ahicks]

Maybe a change to the maintenance schedule, to include more frequent oil changes, is warranted?

For the purposes of this discussion, changing the oil and filling to the proper oil level, then going for a test ride to check the results seems like a worthwhile step towards a solution here. To my way of thinking anyway.

 

[pvanv]

Maybe a change to the maintenance schedule, to include more frequent oil changes, is warranted?

For the purposes of this discussion, changing the oil and filling to the proper oil level, then going for a test ride to check the results seems like a worthwhile step towards a solution here. To my way of thinking anyway.

Wouldn't hurt. When new, I deliver these with the oil showing half way on the dipstick. After 10 or 20 hours (including some hard running), I change the oil and LU lube, and fill to 3/4 on the stick. BUT, since this only happens at high speed, it certainly seems like the issue is over-revving and triggering the ESG at 6250 RPMs. A tach would tell much.

 

[Sea Rider]

OP needs to check if engine has made more oil of its own from the previous oil quantity it was running before to start with..

Happy Boating

 

[BobGlover]

Thanks guys! I checked the oil level in one motor and it was a little over full; looks like it made some oil. I’ll change the oil, be sure to only put about 3/4 full, and keep the throttle down just a bit.

 

[pvanv]

Put a tachometer on it too. anything over 6000 is a problem. If running too fast, go with a prop with more pitch.