Overheat alarm

[Crater]

I have a '94' mercury sportjet 90 in a 18' BassTracker aluminum boat. My question is: Is there a way to test the oveheat & low oil alarms? I ran some sand up into it last week and overheated the engine but no alarm sounded. I don't know how hot is was but there was smoke coming off of the exhaust(paint burning off)

 

[Silvertip]

Re: Overheat alarm

you ran it hot and very likely damaged the water pump. Disconnect the tan wire that goes to the temp sender on the engine. Ground that wire (the end you disconnected, not the one from the sender). With the key on and the wire grounded the horn should sound.

 

[Crater]

Re: Overheat alarm

No Water pump to damage It's a jet drive. I'll test it when I get home tonight. Is there a way to test the sending unit also? I read about removing it and with a ohm meter testing it in a pan with cooking oil heated up, when the oil gets hot enough (what temp should it sound at) the sending unit closes its circuit giving you a 0 reading. Any idea if this will work or is there a easier way?
Bty I have the Clymer repair manual for it but it has nothing about the alarms other than some of the causes of overheating. Some stuff is good but not all I really expected to get.

 

[Silvertip]

Re: Overheat alarm

There are two parts to the system. The horn module itself and the sensors to activate. You need to verify that the horn module is ok. I told you how to do that. The temp sender is a snap switch, meaning it snaps closed, grounds the tan wire to activate the alarm during an overheat. Do the simple stuff first. Test the module. Then use an ohm meter or test light. Tan wire from the sensor to the probe, connect the test light to ground. If the light lights, the snap switch is closed when it shouldn't be. If the test light doesn't light, the switch is open as it should be on a cold engine.

 

[Crater]

Re: Overheat alarm

Excelent help!!!!! I tested both both are working as they should. Horn works when grounded and sensor is open (no light) when grounded.
PEACE OF MIND that everything is working. Thank You for the help. After $40 bucks on the manual didn't prove any good at least someone here had the knowledge to help. Keep up the good work here, I'll probally be back

 

[Silvertip]

Re: Overheat alarm

On some motors the horn sounds briefly when the key is turned on. Don't know whether that's the case with yours or not. What you didn't test is whether the temp sensor works when hot. That requires removing it and testing it in a pan of water (suspended in the water - do not let it touch the bottom of the pan).