Trojan Boat Forum

I have a raw water cooled Chrysler LM318. When I bought the boat, the temperature gauge/sender was not working. I replaced both the gauge and the sender and the temperature reading I get is 100 degrees. I know the thermostat is supposed to be 140 degrees and I'm wondering why my engine is running at a cooler temperature.

The temperature sender that was in the boat when I bought it is located near the thermostat housing and only has 1/8 of an inch from the tip of the sender to the threads. I could not find a replacement sender this short, so I had to install the new sender in the hose from the engine to the thermostat.



Could the sender being located in the hose be giving me a lower temperature reading? The hose tends to be cooler to the touch than the thermostat housing. Thanks for any thoughts.

Sender should be in the intake manifold or thermostat housing . Where its at now it would read too cool .

There was an option for a temp alarm. Those switches are typically smaller. Are you sure it's not a switch rather than a sender? Did you have a close look to see if there is another sender close by? Or is the wire that was going to the small sender now hooked up to your new one and it's actually operating the temp gage?

Did you confirm with an IR temp gun that the gage actually reflects the temp at the engine?

Big D wrote:There was an option for a temp alarm. Those switches are typically smaller. Are you sure it's not a switch rather than a sender? Did you have a close look to see if there is another sender close by? Or is the wire that was going to the small sender now hooked up to your new one and it's actually operating the temp gage?

Did you confirm with an IR temp gun that the gage actually reflects the temp at the engine?

You can see the original sender in the picture below the new sender. The wire that was connected to the original sender is now connected to the new sender. When I ground the wire to the engine block the temperature gauge reads full scale so I know it's the correct wire. It's possible that the original sender is really a temperature alarm, but it was hooked to the temperature gauge when I bought the boat. I didn't see any other senders near by.

I don't have an IR temp gun. When I feel the exhaust manifolds when the engine is running, they are warm but not hot. I'm not too worried about the gauge reading 100 degrees. I'm just trying to figure out why.

You are raw water cooled, your sensor is away from the center of circulation, and its early in the season, so the water temps in your home area are proobably a bit cooler now as compared to July or August. All of these things are probably combining on you to give that low reading.

FWIW, I am RWC as well, and I wil run a bit colder in the spring until the lake begins to warm up. When the water was 38 degrees this April when I launched it took a bit longer than normal to get to operating temp.