Adding temperature sender to '97 Merc 40

[KThomson]

Hello,

I have a '97 Mercury 40hp (s/n 0D128799) and the warning module has decided to act up. I'd like to switch to pre-mix (another topic) and add a temperature sender/gauge. There is a brass plug on the head where I can add the sender but am wondering about the wiring. The remote wiring harness end on the engine side has two wires that are connected together (brown-white + tan). At the throttle side, I have a loose tan wire. When testing continuity, it seems the tan wire from motor end is the same one that is on the throttle end.

• Does anyone know if this is the wire to use for the temperature sender (the jet version of this engine has one)
• What is the purpose of the brown-white wire on the motor end and why was it connected to tan?

Motor end (I have disconnected the two wires to test continuity)


Throttle end (loose wire)


Thanks,
Kevin

 

[Faztbullet]

That control box is common to all engines using the 8 pin connector. Smaller engines will not use all the wires in harness. It is better to add a water 15psi pressure gauge as readings are instantaneous

 

[dwco5051]

I would use the tan wire to install a warning buzzer and add a water pressure gauge. Both have their good points. The pressure gauge will let you know the general condition of the cooling system. If you notice the gauge is consistently reading lower than when the impeller was new you will know it is time to service the pump. The temperature activated buzzer will warn of a condition that may be catastrophic and requires immediate attention and doesn't require constant scanning of the instrument panel.

 

[KThomson]

I would use the tan wire to install a warning buzzer and add a water pressure gauge. Both have their good points. The pressure gauge will let you know the general condition of the cooling system. If you notice the gauge is consistently reading lower than when the impeller was new you will know it is time to service the pump. The temperature activated buzzer will warn of a condition that may be catastrophic and requires immediate attention and doesn't require constant scanning of the instrument panel.

I like the idea of a buzzer. I had been looking for a pressure gauge with a configurable alarm setpoint but did not find anything at a reasonable price. Is there a particular sensor/buzzer combo you can recommend or suggest?

 

[airshot]

Why not just keep up with the impellor maintenence? Need replaced every three years with normal use, every year with extreme service. Not that hard to do.

 

[KThomson]

Why not just keep up with the impellor maintenence? Need replaced every three years with normal use, every year with extreme service. Not that hard to do.

I agree, there is no substitute for good maintenance however, I'd like to have some warning of impending doom if something does go wrong (clogged intake, impeller failure, etc.). If I can't get the original overheat warning working, a pressure gauge seems like a good option, as long as I keep an eye on it.