Overheat alarm on Pa-in-law’s Evinrude?

[mr-asa]

He’s got a (I think) mid 80s Evinrude 60 HP. Recently he has noticed that when he starts it the overheat alarm starts yelling within 5-10 minutes of idling. If he shuts it off and waits for it to cool, then starts it again there are no issues.
It pumps a good strong stream, no stumbling or weirdness I noticed.
100% fresh water, off of the St John’s River system, middle of the state.

It gets stored on the boat, on a hoist out of the water every single time he is done with it.

Anyone have ideas of what to check?

[fleetwin]

Well, those things are designed to run fairly warm/hot at idle…Have you checked engine temp while it is idling with the alarm on?
That engine does not have any of the fancy alarm signals, or fancy self test horn (unless someone has replaced the horn), so it seems doubtful that it is a false warning signal. Probably time for a new impeller and thermostat change.

[mr-asa]

If it were those, I’d expect it to start alarming later on while running, though. Yeah?

Is it possible it being out of the water allows it to drain, and the thermostat creates a vapor lock or something that prevents water from getting to the powerhead until it gets hot enough for the t-stat to open?

[fleetwin]

Don’t think so, the thermostat has a vent hole, and the block is vented through the overboard indicator hose. 5-10 minutes is plenty of time for that engine to heat up enough to sound the alarm. Keep in mind the hot weather we have been having doesn’t help, like I say, those engines run pretty hot at idle to begin with.
Try revving the engine in neutral (no more than 3000RPM) while the overheat alarm is sounding. Increasing RPM like this pushes the cooling relief valve off its seat allowing more water to bypass the thermostat. If the alarm shuts off while the engine is revving in neutral, then most likely the alarm is telling the truth. It should only take about a minute or so for the engine to cool down some (enough to kill the horn) while revving with the relief valve popped off its seat.
But again, the hot temps down there might just be to blame. You mentioned that this problem only occurs once, then it is fine for the rest of the day.

[jeff-register]

I believe Don has it right. My 1978 85hp acted the same until it recieved a new T-stat & impeller made the difference with mine. I NEVER rev it up any more than 3k too. Even that high is questionable I feel. Running that high without a load is just waiting for a runaway .I’m very careful with that much hp.

[fleetwin]

Jeff, you are right, my advice was questionable concerning revving that engine up in neutral, it will run away on you….
I will amend my advice to saying get the boat in the water idling in gear until the horn comes on, then give it the gas for a minute or so to see if the horn shuts up.

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