Strange overheating alarm on 2008 Honda 135

Ferg

If I suddenly take the RPMs down from cruising speed (4400rpm for me) to idle speed, I get an immediate overheat alarm. I shut down and restart, and go on my merry way. It's happened twice now.

Engine has been flushed with Salt-Terminator after each use, new thermostats, newish impeller, good flow from the pee.

I'm guessing it's the sensor switch gone bad.

Thoughts?

thataway · Posted: Sat Sep 23, 2017 6:27 pm Post subject:

I saw the same thing on a 150 which I had been running fairly hard, and brought down to idle. The flow seemed to be fine--I suspect that there was some localized overheating--and in the case I had, I brought the engine back up to a fast idle.

I always back down, and make sure that I have not caught a piece of kelp or plastic over the intakes when I get an overheat, I had one time at Powell, that there was so much fine debris in the water, (up San Juan arm), that I had an overheat alarm. I stopped, backed down, and then shut down, and cleaned off the intake--resolved the issue--and I turned around and didn't go further into the debris field.

BrentB · Posted: Sat Sep 23, 2017 6:31 pm Post subject:

Could be sensor(s) or a failing thermostat?

How old are the thermostats?

Ferg · Posted: Sat Sep 23, 2017 8:58 pm Post subject:

Dr. Bob, there was no debris and the intake was clear, that's why I'm thinking it's a questionable sensor.

Brent, the stats have less than 20 hours on them, and I think that if they would have failed, it would be at high RPM

BrentB · Posted: Sat Sep 23, 2017 9:31 pm Post subject:

Thanks

Can the OB be connected to computer diagnostic software?

Yamaha has one called YDS

Ferg · Posted: Sun Sep 24, 2017 6:28 am Post subject:

It does have a diagnostic port. That's my next step, but I don't know if the history will show these two events. We'll see

South of Heaven · Posted: Sun Sep 24, 2017 7:47 am Post subject:

Are you sure its an overheat warning? My old Suzuki once had an alarm go off and I couldn't figure it out. Then i came to find out it was a reminder for the oil change. The previous owner must have set it to go off at a certain time interval.

Do you have a battery operated temp gun? If you're absolutely sure it's an overheat alarm then I would take off the cowling immediately after it happens again and get different readings from different parts of the block (assuming theres no plastic there). Those guns are very accurate. I bought one and use it on my volvo engine in my new boat.

Ferg · Posted: Sun Sep 24, 2017 8:26 am Post subject:

It's defiantly an overheating alarm, but as I mentioned in my initial post, it only happens when I suddenly reduce the RPMs. I shut down the engine and immediately restart with no problem and no alarm. If was truly overheating, it would go back into alarm I think

Jack in Alaska · Posted: Mon Sep 25, 2017 12:58 am Post subject: over heating???

My 2003 200 hp Honda did the same thing 3 yrs ago. After much typing and a-s scratching it turned out to be the thermostats.
Has not done it for 3 yrs now.