The Boating Forum - Mercury Outboard Temperature Sensor

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Pat Lange
07-14-2006, 01:46 PM
I have a 1993 Mercury outboard, 3 cylinder, 90 HP. It has a temperature sensor that is supposedly conected to a temperture gage. The gage has never moved so I figured the gage was bad. I installed a new gage but it too did not register anything.

I heated up the sensor outside of the motor and got the alarm on the motor to sound so I believe the sensor works. The sensor looks like a bronze probe with a single wire connected to it.

Question: does this type of sensor provide a signal that can be registered on the gage or does this sesnor only sound an alarm if the engine gets too hot, thereby making the temp gage nothing more than a decoration on the dash board? ;? ;?

07-14-2006, 03:40 PM
I don't think that one sender can be used to supply a signal to two instruments.

What color wire is connected to the S terminal on the instrument and what color wire is connected to the sender? If they are different colors, can you try and find where the wire that goes to the S terminal of the gauge is located at the engine? Just follow it from the gauge to wherever it goes. Not easy but it has to be done.

07-14-2006, 09:54 PM
The sensor you are describing is for the alarm only. The one with the phillps screws holding it. You cannot use it for anything else. The Tan/blue wire. The temp gauge is nothing more than a decoration on this engine no matter what you do to it. It will not work correctly the way the cooling system is designed. This engine just dosen't get hot enough meaning hold the heat. None of the In-Line Mercs did. The gauge will barely register if antyhing at all. The thermostat is only set to 120 degrees. And even if it did you would still have to have water in the block to heat the sensor the screws into the pipe plug. I.E. pump failure. Typical Force O/B senario years ago. The gauge worked because of the 143 degree thermostat but again ONLY if there was any water in the block.

The alarm sensor is always a dry heat type for metal contact. The aluminium is gaurrateed get hot no matter what. The V-6 temp gauge was designed this way thats why it worked correctly. There is no such provision for that that style sensor on your motor.

The voice of an experienced Merc tech will tell you don't bother. Replace it with a water pressure gauge. 0-15PSI and leave the O.E alarm alone. It works just fine. The alarm is set to 195 degrees. That is very low for an O/B. These don't like to get hot.

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