Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

I had a bit of trouble when I tried to flush the engine after three hours of boating today. I didn't see any water coming out of the hot water holes of the engine but I thought this was just because the thermostat wasn't open. The overheat horn sounded after about a minute and I shut it down. It's odd that I was able to run the engine for three hours without trouble. When I tried pressing the engine flusher tighter onto the engine I heard a little water movement in the low end and finally noticed some warm water coming out of the hot water holes, but not like it usually does.

Could the thermostat have gone bad?
Could the impeller have broken?
Could I have something blocking the coolant passages?
Because the overheat horn sounded could I have damaged the engine by running it hot?

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

99% impeller. you can check your compression, to see if the head gasket blew. impellers are like that. they can just quit. becareful with the shift wires when dropping the lower, tie a string to them so you can fish them back up.

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

sounds just like mine. impeller. easiest thing to change. have you changed it before? My overheat alarm started to go on intermittently. I also still had water coming out the exhaust relief holes. looking at my impeller its a wonder that water could have still been circulating. If you shut your engine down right away your engine should be ok.

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

Thanks, I'm pulling the low end apart right now.

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

The impeller was okay. I ran the engine after reassembling it and had the same problem. I put it into forward gear still nothing. I then gave the engine a little burst of throttle and it started working. Where is the thermostat in this engine? Does it even have one?

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

i believe your thermostat is below your pulse pack. I haven't had to mess with mine, so i'm going to leave that info for someone else. When you say your impeller was fine, was there any cracks? did you take the impeller out?

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

When I said the impeller was fine, I meant that it was in one piece. It has cracks and needs to be replaced. I put it back in to use because I have a $25 one on order as opposed to getting a $50 local one.

How long have you had your motor for?

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

Although this might not be the case with your problem, be aware of the fact that the hot horn works when the circuit in completed to a ground. When the motor gets hot, the sensor closes the circuit and the horn sounds.

Because the horn works this way, if there is a frayed bit of wire anywhere in the circuit, and that allows it to ground, your horn will sound. You might want to carefully check to make sure the motor is really getting hot. In doing so, however, I would watch the water flow very carefully, and make sure that the thermostat is opening. If there are any signs of the motor overheating, shut it down asap.

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

The engine did definitely get hot. It seems to me like the thermostat is a bit sticky. I have not been able to find what thermostat this engine uses. Any idea where I can find one?

Re: Overheat horn sounded while flushing the motor - 1972 100HP Evinrude 100293

Your engine uses a vernatherm (thermostat) PN 384719.

Follow the large hoses from the bottoms of the cylinder heads to the thermostat cover.

Parts are available through any local BRP dealer:

http://dealerlocator.evinrude.com/EN/?Rnd=1172157085156

or: http://shop.evinrude.com/