temp on a 74 evinrude 115

[kevinr]

I'm adding a 120-240 deg temp gauge to my dash to monitor a 115493b (1974 115hp evinrude).

Couple of related questions:  (1) did that motor come with a sensor/sending unit on on the motor? (2) can I add a universal screw in to a blind threaded hole (i know i'll have to match the scale of the gauge)?

Last question - it has a warning buzzer in the throttle control on center console (aquasport 19-6). looking at a diagram of the wiring harness from the motor, it *appears* that is wired into the tach, though most of the warning buzzers i've seen are either temp or oil pressure related. What does this do?

Thanks all.

[Capt. Bob]

I'm guessing it is indeed an overheat buzzer. Can you see what color wires are connected to it? Purple and brown/tan?

It probably came with a temp sensor from the factory. Might have went the way of the Dodo after all these years.

[kevinr]

purple brown red black best I can tell. purple and red to 12v pos. black to 12v ground. brown to sensor. if its just a buzzer, i doubt its sensor gives off a range of readings - just on when it hits a certain temp. if thats the case, i can ditch the old stuff and use its wiring for the new one.

[Capt. Bob]

if its just a buzzer, i doubt its sensor gives off a range of readings - just on when it hits a certain temp.

You are correct in that it completes the ground when it hits a certain temp range and sounds the buzzer. If you have a gauge attached, then the reduced resistance caused by the heat causes the gauge to move and you then get a reading. Some sensors are placed in the water jacket, often on the top of the block. Others are just mounted against the outside of the block. Both types work on the same principle. On newer motors you get the benefit of not only the sound but often a reduction in motor rpm. Many times, the damage is done before you notice the overheating on just a gauge, unless you have a designated "gauge watcher".

Good luck.