How to Add a Water Temp Gauge to a Yanmar Diesel

How to Add a Water Temp Gauge to a Yanmar Diesel

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When you wish to add a temperature gauge to your Yanmar diesel engine, you can use the thermistor already in place in the engine. In gasoline marine engines, the thermistors that show the engine's temperature are placed in each cylinder. In the Yanmar diesel, the thermistor that triggers the warning light -- the Yanmar uses a warning light, rather than a gauge -- is placed in the coolant line. This thermistor tracks the motor's temperature and triggers the warning light at 195 degrees Fahrenheit.

Items you will need

  • Hole saw

  • Drill

  • Screwdriver

  • Wire crimper

Preparing the Dashboard

Step 1

Trace the outline of the gauge template, provided with the gauge, onto the dash. Note the size of the gauge specified on the template. Select a hole saw of that size and install the hole saw in a drill.

Step 2

Inspect the under-dash area to ensure that the location you chose for the temperature gauge is adequate. Re-route or reposition any wiring or hoses in the area so that, as you drill the hole for the gauge, you don't cut through essential wiring or hoses.

Step 3

Center the hole saw in the tracing from the gauge template. Cut the hole in the dash.

Wiring the Gauge

Step 1

Remove the screw from the power terminal of a gauge adjacent to the temperature gauge's position, using a screwdriver. Insert the screw through the ring terminal on the red wire of the temperature gauge. Thread the screw back into the the power terminal of the adjacent gauge and tighten the screw securely.

Step 2

Remove a screw from the common ground under the dash. Insert the screw through the ring terminal on the temperature gauge's black ground wire. Return the screw -- along with the attached ground wire -- to the common ground.

Step 3

Disconnect the blue-and-white thermistor wire from the engine temperature warning light. Pull the wire up through the hole prepared for the temperature gauge. Crimp a ring terminal onto the blue-and-white wire, using a wire crimper.

Step 4

Remove the screw from the "S" terminal of the temperature gauge. Insert the screw through the blue-and-white wire's ring terminal and reinstall the screw in the gauge's "S" terminal.

Step 5

Lower the temperature gauge into the hole prepared for it. Use the screws provided with the gauge to secure it to the dashboard. Press the trim ring into place around the face of the gauge.


  • Disconnect the negative cable of the battery before performing any maintenance work on the marine engine to prevent electrical shock or accidental starting. Remove the nut from the negative post, using a 5/16-inch box-end wrench. Lift the cable from the battery, move it outside of the battery box and close the lid of the battery box. After the work is complete, reconnect the negative battery cable.


  • The normal operating temperature of a Yanmar diesel should range between 150 and 180 degrees Fahrenheit.
  • If you leave the other wires in place on the engine temperature warning light, the warning light will warn you of high or low oil pressure.
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