Is this overheat buzzer behavior normal?

​So I have a 1986 Yamaha 40 with a fresh powerhead. Only a couple of hours on it. Starts and runs like a champ. Idles nice, accelerates under load without any hesitation, etc...

Had it out two days, one hour running each day and the went like this both days:

Started like a champ
Idled out through the no-wake zone (ok, well bumped it up to 1000 rpm just to get out there faster), about five minutes
Drive around at 3000 rpm
Drive around at 4000 rpm
Find a place to beach and swim and eat lunch for an hour or two
Fire back up and motor around between 3000 rpm and 4000 rpm
all perfectly normal operations
Idle back through the no-wake zone to Drop wife off at the dock to go get the trailer (well trained wife)
back away from the dock and find a shady place to shut down while I wait for her (Mojave Desert Lake Mead 100^F outside)

Wife shows up with the trailer, fire it back up after sitting 20 minutes shut down and... overheat horn starts up at idle. Since I am in the marina, I cannot bust up onto plane to see if it goes away. Horn keeps going as I idle back onto the trailer. Embarrassed.

This same chain of events happened pretty much as describe, two days in a row.

Outside air temperature low 100's, water temperature low 80's, telltale stream looks healthy at idle and under way. My 2.0l 150 and 2000 Mercaha 90 FourStroke handle these conditions just fine. Never an issue.

Any ideas?

-Peter

previous saltwater use?impeller good,no obstructions?thermostats and popoff 100%?might be time to do descale/flush with harsh chemicles in tub of solution like muratic acid/rydlime..search you tube

Would those be reasons it would overheat at idle? And only at idle after it's been running then sitting? It doesn't seem to overheat at idle when you first fire it up and then drive it out through the no wake zone. Nor does it overheat when planing 3000-4000 rpm. Just after sitting then idling. So far.

Well damn. It was used in salt water in the past... a little. Probably 25 hours. No more than 50. But the rebuilder (very well known and respected around here), did a super neat job. On the outside there's not a spec of grease and it it appears repainted in factory color paint, carbs clean, new (looking) overheat sensor. Seems like his did his best to take my used powerhead with a scored piston, and send back something as close to a factory new powerhead as possible. It also fired right up like it had been running the whole time. I'm assuming by the state of cleanliness of it, that any corrosion issues in the powerhead were cleaned or replaced. This rebuilder is in a salt water area, so he should be no stranger to it. I sent only the powerhead to him.

The mid has no evidence of salt whatsoever of any kind.

Nor does lower. The lower was re sealed with a new impeller back in 2018 and not used until a couple of weeks ago. Maybe the impeller aged as it say unused? That's certainly the easiest thing to check, so I will.

Thanks a bunch for getting back to me.

-Peter

Overheat alarm and low oil alarm are the same on mine. If you still have oil tank could be that sensor. If you change water pump, get the whole kit from Yamaha it has the metal housing in it. If you have a infrared heat gun, check the block temp.

Quote:

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Originally Posted by CRH1

Overheat alarm and low oil alarm are the same on mine. If you still have oil tank could be that sensor. If you change water pump, get the whole kit from Yamaha it has the metal housing in it. If you have a infrared heat gun, check the block temp.

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Great points!

I am running pre mix now. And out of ignorance, I have “disabled” the oil sensor in a very shade tree way… I put the oil tank sensor inside the cowl, upside down so it the float is always on “top”. I’d like to just remove it but I haven’t put in the time to figure out which way to jumper the wires on the switch box/power pack, so it doesn’t go into limp mode. Sounds like you know this motor pretty well. Any tips?

Also, with the rig job like I have it now, I get the “green” light on the three light indicator, which makes me think my rig is working at least as far as tricking the oil level sensing safety. Still I’d like to be without it.

I do have an IR temp gun. What temps should I b looking for?

-Peter

I don't have any lights for alarms, just a horn. So with your lights, you know it's temp not oil, that's good. The high temp switch switches around 180 deg F. I have never checked my temp with gun. I think 150 degf would be fairly normal temp. Have you changed comlete water pump kit? Is thermostat clean?

Still happening. Only at idle and only after having been shut down and heat soaked.

-Tested the thermostat. It opens nicely.

-Water pump looked Ok. (gear case has a leak around the bearing carrier which I will fix but that shouldn't have anything to do with it)

-With the lower off and the thermostat out, I blew air up the water pickup tube without the thermostat. Air comes out the telltale, just as water comes out when under way.

-does this motor even have a poppet? It doesn't show anywhere in the powerhead section of the factory service manual

So no full blockage, but does that mean we are down to the possibility that there is a partial blockage? Or maybe some diverter plug that goes in the coolant passages of the head, (it's a three cylinder 40hp). But the factory manual does not show anything about it if there is one.


And how is it that this only happens at idle/low power? Could it be that at higher power/rpm, there is enough flow whereas at idle there isn't? I do get a nice slow idle out of it. Maybe I need to bump it up a bit?

-Peter

No poppet on this motor. Partial obstruction is a possibility, but I would think the rebuilder checked/cleaned water passages. Did you check block temp with IR gun? You can also remove the high temp switch and check it like you did thermostat. It should switch around 180, if it switches at 150 or so, that's too early. Could also be low water flow/pressure, a complete water pump kit would eliminate that.

Ok thanks for that.

I don’t know how slow the overheat sensor works, but with the button in a pan of boiling water and… nothing. Even after several minutes of exposure. I tested my continuity buzzer repeatedly by touching the test leads to each other, to the pan etc…. So this adds suspicion to the sensor…

… except …

I hit the head with my IR gun while idling with the buzzer going and I got 190+. Of course this was in the Mojave Desert sun and 100+ degF. Still with the cowl off and the engine off while the wife went to go get the trailer, it cooled down to 120-130 on the IR gun, and the buzzer stopped.

So… the sensor might be suspicious in the pan of boiling water, but the buzzer behavior was in line with the IR gun and the buzzer.

I will dig into the water pump situation and pursue that first. The lower is at my friend’s shop getting re sealed and pressure tested. So I’ll get after the pump then.

Thanks for everything so far.

-Peter

That's good data. The IR gun info tells me it is overheating. That means low water press/volume or restrictions. I assume no water pressure gauge? I would change water pump assembly first, look for anything wrong. A pinched tube, pinhole in tube etc. If that don't fix it, Remove the cylinder head.

​So… Solved.

It turned out to be yet another of those damning confounding things you see in boating from time to time.

After not using this boat for a month or so, I got back to it today. On the muffs I idled it with the IR gun. After about ten minutes, it went over 180 and started buzzing. Let it cool, pulled the old thermostat and fired it back up. Telltale steam never got more than lukewarm, and was stronger than with the thermostat. So on a hunch, I put in a brand new thermostat from ProMarine, which is where I usually get gaskets and carb kits and impellers and such. Worked like a champ. Got up to maybe 130 tops. And telltale flow was much better too. Success.

So here’s the maddening thing… new thermostat solved the problem but… I had tested the old thermostat in a pan of boiling water and seemed to test out OK. Started opening and was fully open way before boiling. So I had ruled it out as a cause. Yet. Somehow. A new one fixes it. :shrugs:

-Peter