Temp guage not resonding

[70mustang]

Greetings fellow boaters,<br />My temperature gauge seemes to be not responding as in the past. It used to range from 100 to 175 degrees. Now it's barely goes past 100. I have a 3.0 Merc I/O built 1999. I took out the temp sensor in the block just below the t-stat and it looks clean. Water came out and the engine does not get hot so I know my water is circulating. My question is how can I either test the guage or test the temperature sensor in the block before I go and replace either one? Can I short out the guage to test it? Can I somehow test the sensor?<br />Thanks in advance for some advice.<br />Marty

 

[Don S]

Re: Temp guage not resonding

Put your hand on the thermostat housing, if it feels barely warm, then the sender is ok. If it's fairly hot, then the sender is bad.<br />If you have a raw water cooled engine, the stat may be sticking open (common) and causing the low reading. But a stuck open thermostat is also allowing hot spots in other parts of the engine.

 

[70mustang]

Re: Temp guage not resonding

Thanks Don,<br />I felt the engine and it seemed warm to the touch not very hot and not a temperature difference from the past. So, that means the sensor is responding and you suggest the t-stat stuck open which will allow the raw water volume cooling the engine too much. I never thought about the t-stat, sounds like a good place to start.<br />Thanks again Don,<br />Marty

 

[Rhadley]

Re: Temp guage not resonding

I'm surprised you get a reading as low as 100 even if it is stuck! Are you on a lake with cold water? Around here, water is 89 degrees right now.

 

[rbezdon]

Re: Temp guage not resonding

Also, check the wiring to the sender. The reading you get if the wire is open some where is low temp. It could be as simple as the connection of the wire to the sender is oxidized a bit. Clen and check the connections. One way to test is ground the wire connected to the sensor (the nut on the top center of the sensor. If the connections are good all the way back to the guage the guage should go to "fll hot" while the wire is grounded. Remove the ground and everthing is back to normal. If this works chances are the sender is bad. I saw a posting here yesterday with a link to trouble shooting this system, gorgot who posted it though. A search may turn it up.