9.9 Tohatsu warning light problem

[BobGlover]

I’ve got two Tohatsu 9.9 outboards. Both are great motors, but when I’m running full throttle, occasionally I’ll feel a miss in the motor, look back, and the red oil pressure light is on; the motor stills run fine. I then back off the throttle to ‘idle’ and the light goes out. I’ll go back to ordinary running and everything’s fine. What causes this to happen? Will this harm the motor?

 

[pvanv]

We need your exact model... But, it sounds like you are over-revving and hitting the rev limiter. That could be caused by a bad prop, wrong pitch, or motor jack height too high.

 

[BobGlover]

Thanks Paul; this is kinda what I was thinking. The props both came with the motors, are in good shape and the boats are 15’ transom (short shaft motors). Will hitting the rev limiter hurt the motors, if you back off the throttle. Also, a friend’s 9.9 Mercury does the same thing. Since it’s made by Tohatsu, I guess it’s the same situation?

 

[Sea Rider]

Will need to install a good quality induction tach to check if the motor is over revving badly way over the max wot rpm factory stated range to rule out if the rev limiter is indeed kicking in. Could the oil pressure switch be bad on all 3 mentioned motors ?

Happy Boating

 

[km1125]

Can these motors foam the oil like the smaller motors? Could that be causing a momentary drop in oil pressure?

 

[pvanv]

Yes, if over full.

 

[MattFL]

Pick up an hour meter with tach on Amazon, you can probably find one for $20. In addition to making it super easy to schedule your maintenance, if you get the right one it will remember max RPM. This is the one I have on my motor. Now when this happens you can stop and check the stored max RPM and compare it to the max RPM specified in the owners manual. Generally speaking, bumping the rev limiter on occasion won't kill the motor, but running it right up next to the rev limiter for extended periods will definitely shorten the service life. If your oil pressure really is getting low, then that will kill the motor very quickly so you want to figure that out, or at least figure out how to prevent the oil pressure from dropping.