Honda BF90 overheating rev limiter?

C

croakz

New member
Hi all,

My 2000 Honda BF90 sounded the overheating alarm yesterday (Only our 4 time out with it). Stopped the boat, alarm turns off, overheating light is on, water is coming out of the tell tale. Started moving again and the alarm goes off at 1500 RPM. Below it, seems to run fine. Limped back to the marina and docked in neutral I can use the choke \ fast idle lever to get the alarm to sound at 1500 RPM. I can't find any documentation on the rev limited, is this a known threshold?

I have new thermostats and SaltAway coming, but the very specific rev limit makes me wonder if it's a sensor?

Thanks for any help.

- tom
 
I would be looking at the water passages in the motor. Honda's do have a reputation of a little more corrosion than some other brands. Salt away is something to use every time. It may take stronger acid if there is really a problem with the passages. The tell tale basically tells you if the water pump is working...but not about corrosion or narrowing of passages. If the engine went into limp home mode, then I would be concerned. Yes it could be a sensor, but just or more likely there is some issue.

I had a new to me boat with the same issues. It was the passages and we did have to clean them. Put in a new thermostat while we were at it, and also re-did the impeller.

Page 90 of your manual:
Engine Oil Pressure and Overheat Warning System
If the engine oil pressuredrops and/or the engine overheats, either or both warning systemscould beactivated. When activated, the engine speedwill decrease gradually, the green oil pressure indicator light will turn OFF, and the red overheat indicator light
will turn ON. A continuous buzzer
will sound on the remote control type.
The engine speed can not be increased with a larger throttle opening until the Mal function is corrected"
Click to expand...

The rev limiter generally kicks in at 6,000 RPM or slightly more. This prevents excessive engine speed if the boat is under propped.
(or hub/prop dammage)
 
It could be a sensor. However, since it goes off kind of leads me to thinking it really is an overheating condition. It's getting just enough cooling to be happy at idle, but you when give it the coals and it starts making heat, it can't keep up. You could very well have a partially stuck thermostat or things could be plugged like Bob notes. I do know that one can put your hand on the valve cover of a properly running honda outboard and hold it there for just about ever. One that is overheating you will find yourself taking it off rather quickly. It's not a perfect diagnosis, but it will give you an indicator or what is going on. If you have an infrared thermometer like I do, the head is around 150 degrees or so at idle and actually gets cooler with rpms. Well....at least the ones I have do.
 
The 1500 RPM limit is throwing me, we went from Vashon back to Des Moines for about an hour at just under 1500, and if the needle went above, alarm. Just seemed very specific. I do have an IR thermometer, 'll check the temps when I replace the thermostat.
 
My 2004 Honda had a sensor issue in the fall. It was easy to test, if I started the motor cold the alarm was going off and light on. Shut the motor off and unplug the sensor and start motor and alarm and light went off. I wish I figured this out on the water instead of the driveway. We thought we had a serious issue and had long slow ride back to the launch last fall in limp mode.
 
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