1993 Evinrude 70 hp overheat alarm

[StevetheSkate]

Strange one this, a couple of weeks ago I was going out for a few hours fishing, started up as per normal, engine sounded fine, after about 5 minutes all instruments were on and we were all good to go.
Eased forward on the throttle only to be welcomed by the sound of the overheat alarm, plenty of water pumping, turned her off, left a wee while, started her up again, same again, alarm straight away, even just on the key, one turn to the right, without starting her up, I decided that was that, and cancelled the day, got a pull back in, loaded her back on the trailer and run her up to the menders, as the engine was just a few hours short of its 100 hr service I decided to have it all done at the same time and save another trip up there.
Following day I get a call to say that the alarm was a faulty sensor and it would take a few days as they come from Belgium, ok I'll wait . Get the boat back after 4 days , new service and sensor, great, back out to sea started her up, all appeared fine, moving around for 20 minutes or more at 2000 / 2500 revs, all working fine , pushed up on to the plane and at 4000 revs off goes the alarm again, plenty of water pumping and not a lot of heat from the engine.
Back up the menders, we took her out for seatrials and same again at 3000/4000 revs off goes the alarm, the technician takes the engine temp, no problem, loads of water pumping, no earth faults, must be a dodgy sensor, left the boat with them as they ordered another sensor from Belgium, they fitted the new one and took it out on sea trials again, same thing happened, they decided it must be a fault between the sensor and the alarm horn in the remote, so they run a separate alarm cabling from the new sensor to the new alarm which was located in the cabin.
Took her out yesterday, as soon as it got up to 4000 revs off goes the alarm again, any ideas anyone out there.

 

[boobie]

Re: 1993 Evinrude 70 hp overheat alarm

Just a thought. You may have some high voltage in your battery charging system or a bad horn.

 

[durban]

Re: 1993 Evinrude 70 hp overheat alarm

i stripped this one to find out wot it looks like inside i get very nosy & want to know as my brain was ticking over , because when, i put the meter on it , it showed that the circuit was closed , meaning the motor is overheating , but it was on my work bench . inside it there is a bi metal little disc that convects in to a dome , this dome moves in & out with changes in heat , so when the motor gets hot the dome pushes a little pin ,this pin then pushes on to one of the contacts like the points of a car then then it closes the circuit , when it gets cold the dome moves back & opens the circuit . mine was cooked the dome was not pushing in & out i think the very thin little disc dome plate was exposed to too much heat as it was the sensor down by the exhaust outlet , my advice is change yours helluva job to open them up : from right to left in photo : LITTLE DISC WITH DOME, CERAMIC DISC WITH PIN IN CENTER , METAL SENSOR COVER cheers

 

[Faztbullet]

Re: 1993 Evinrude 70 hp overheat alarm

when, i put the meter on it , it showed that the circuit was closed

It will be on that sensor as its the thermoswitch for the choke.(purple wires)This switch supplies voltage to the choke solenoid which holds the choke shutters in a "warm up" position. This is why the choke has 2 leads and jumps when you turn key on. When engine reaches temp the switch opens to release choke from warm up. The overheat switch has one wire and is open till it gets hot then closes completing ground to horn.
Steven if all your getting is a alarm and no shut down on engine look for a wiring problem(pinch or rub thru) as yours should have the pack that reduces rpm if alarm is triggered, also check to see if t-stat is stuck open....

 

[seahorse5]

Re: 1993 Evinrude 70 hp overheat alarm

Steve,

Yours does not have a choke sensor temp switch.

I could not see from your pictures but does the new temp switch have a tan wire with a blue stripe on it, or is the wire all tan colored?

IF the motor is run in saltwater, deposits build up in the cylinderhead and can cause hot-spots such as near the temp switch location which will cause it to activate even though the engine is not overheating.

Is the motor slowing down to 2500 rpm in its SAFE mode when the horn goes off? Has the thermostat been checked and does the pressure relief valve move off its seat OK when the water pressure increases? Often salt buildup under the valve grommet cause it to stick in the closed position giving a high speed overheat condition.

 

[bob johnson]

Re: 1993 Evinrude 70 hp overheat alarm

It will be on that sensor as its the thermoswitch for the choke.(purple wires)This switch supplies voltage to the choke solenoid which holds the choke shutters in a "warm up" position. This is why the choke has 2 leads and jumps when you turn key on. When engine reaches temp the switch opens to release choke from warm up. The overheat switch has one wire and is open till it gets hot then closes completing ground to horn.
Steven if all your getting is a alarm and no shut down on engine look for a wiring problem(pinch or rub thru) as yours should have the pack that reduces rpm if alarm is triggered, also check to see if t-stat is stuck open....

you have enlightened me!!

I have alarm issues, and I finally got tired of listening to that go off every so often, that i unplugged BOTH sensors... well it didnt work and the dang thing still goes off...but...i left them off.(unplugged)

sure enough it seemed my motor wasnt starting as good...it took a long time to fire over many cold mornings this past month... i finally pulled the primer solenoid and installed another...same issue... so i have been turning the red lever up to start the motor in the morning for the first time...


now i am thinking it might be because my 2 wire sensor is disconnected!!!

luckily I have a 70 hp eveinrude, which is why i read this thread..... I generally just read threads on stuff i have..

now i might still cut that dammm horn out...... it used to do it exactly 2 minutes after i start the motor and it blares for 10 seconds and shuts off..

lately it has been coming on while running and blareing for 10 seconds...but the temps are good 140- 170


bob