Temperature Gauge Stuck

[ceeg52]

Boat: 2004 22' Sundeck:

Was on the boat yesterday and noticed that the temperature gauge was reading 170 degrees. Since I had been in a no wake zone for 15 minutes I knew the temp was too hot. I checked the temperature on my Smartcraft readout and it read 152 degrees. When i got back to the dock and let the engine cool down i confirmed that the gauge needle was actually stuck at 170 degrees. Before I change the gauge is there anything thing else I should look at that would cause the gauge to stick at 170?

 

[Boater420]

I was told if the needle on any gauge doesn't reset to 0 when the key is turned on there is a problem with the gauge itself. The needle is supposed to be able to swing from min to max on the dial without issue.

Since it's a temp gauge, after the engine cools off the needle should return to 0 when the engine is cool. If the engine was running and the temp gauge was at 170, maybe a stuck thermostat, but since it's cool I'd say gauge for sure.

 

[BillK2632]

Here is a simple process to test out the guage and sender:

Water Temperature System (Inboards & Stern Drives)

1. To test gauge, voltage from "I" to "G" terminals must be 10-16 VDC. No wire on "S" terminal. Gauge pointer should rest below 120. Next, connect the "S" terminal to the "G" terminal (leave "I" and "G" terminals connected). The gauge pointer should rest above 240.
2. The resistance of the sender can be measured to determine the sender's correct operation. Remove wire to gauge. Connect an ohmmeter to terminal of sender and to engine block. Approximate values are: 75 (room temperature) = 600 to 800 ohms; 212 degrees = 55 ohms. (These are single station values- twin station values would be 1/2 these numbers).
3. If sender is shorted (0 ohms) gauge will read above 240F.
4. If sender has infinite resistance (Open) gauge will read below 120F.
5. If the gauge reads lower than expected, was sealer used on the sender threads? (See illustration.)
6. The accuracy of the system (gauge, sender, voltage range) can vary as much as 16 degrees at 180F.
7. Use of pipe extenders to plumb both a sender and temperature switch (for horn or warning light) from one port is not recommended. The amount of weight extended on the fitting of a vibrating engine could cause fatigue-related breakage. Also, the sender is removed from water flow inside the engine and will probably read cooler.
8. Teleflex does not offer senders for metric threaded ports.
9. Dual Station installations:
   • When replacing one gauge in a two station installation, the second gauge may need to be replaced as well.
   • Mixing two gauges from different manufacturers to one sender may cause an error in both gauges.
   • If one gauge fails the second gauge will read much higher than expected.
   • If sender fails "open", both gauges will read below 120F.
   • If sender fails "short", both gauges will read above 240 degrees.
10. Twin engines: It may be helpful in troubleshooting to switch either the senders or the gauges from engine to engine.