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Overheating sensor

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Danny94

New member
The overheating alarm keeps going off on my 1997 Yamaha 70HP 2 stroke. As a last resort I am replacing the head gaskets after cleaning out corrosion. I’m just wondering if I can test the sensor while I have it apart. Is it something as simple as putting it in or against a cup of boiling water and seeing if it goes off? Is so, at what temp should it go off at? I'll probably replace it anyway but am curious to know it it does work ok. Also, when I put it back in the hole before putting the head cover on, do I just put it in the hole dry or should there be some conductive material between the sensor end and the metal of the head?
 
I am not familiare with your particulare motor but as to alarm sender there usualy just on or off, like the old idiot light for oil and temp on cars. Befor you go for the head gaskets. With the motor cold pull the wire off the sender and meter the sender to ground. If it is shorted to ground replace it. Sometimes both the temp and oil alarm are tied together so you may want to check that one also.

By the way when the alarm goes of is right after you start or after running for a time?
 
Thanks Nixes. The alarm used to go off when I got into high revs (over 4000), now it goes off after a few minutes at low revs. It never goes off at idle with the muffs on. I started with the water pump then replaced the thermostat and cleaned out the corrosion around the exhaust side of the head. It worked well for a few trips and I thought it was ok, but then it started going off straight away. I've taken the head off and it was badly corroded. I'm going to put a new head and head cover on it to minimize the risk of pinholes, and thought I might as well make sure the sensor is ok while I'm at it. I'm still a little way off that though as I have a couple of broken head bolts to deal with first :( Cheers
 
Danny

Sounds like you are well past checking the senders. If there is that much crud in there then your right you have to give it a good clean out and go from there. Sounds like you have a lot of hours and probably keep it in the water.

good luck

Nixes mate
 
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