system monitor/water temp fault

[carolinacoast]

We just moved the boat about 400+ miles and had the heat exchanger rebuilt on the port engine prior to departure. 200 miles or so into the trip, the water temp sensor on that engine went off, even though the engine was happy in the 160' range. the dumb question for you experts is: how to I determine whether the sensor is bad or there is a fault somewhere in the actual monitor system box? Thank in advance.

[GJH]

Take a little jumper wire and put it across the terminals on the sensor. If that stops the alarm, then it is the sensor. If not, give Roger Wetherington a call. His number is on here, or you can call Sam's and they'll get you in touch. They will also sell you a new sensor (and tell you where to find it on the engine).

A jumper wire or two, say 16Ga, with alligator clips on each end comes in really handy on a boat.

[SKYCHENEY]

The fault can be in one of three places: The sensor can be bad, you could have a bad wire, or you could have a bad board.

Do as George describes to check the sensor. The same procedure can be done at the terminals on the board to check for a bad wire. If neither of the first two test solves the issue, then it is in the board itself.

[rwetherington]

If George comes to one more of my classes he will be able to teach the course. He is right on how to check the alarm

[rmatt]

If you had the cooling system apart, you could have a bubble of air where the sender is located and causing the sender to activate. Ask me how I know.

[carolinacoast]

Thanks to all for the tips. It turns out that after following your advice without success that the culprit was a W171 dip 14 magnecraft circuit on the board of the monitor that decided to retire. After eliminating the other suggested culprits I swapped another circuit on the board and the problem disappeared. For $7 per circuit, I decided to buy 2 and just tape a 2nd on the board in case another fails. It still is not wired correctly since the silence button never works on either the lower or upper helm. I just need to take a picture and ask the guru Roger for guidance. Merry Christmas and thanks to the forum for another problem solved.

[JLR]

Great result. I am having the same issue. Roger is helping me out , as well. Can anyone tell me whether the sender depicted here is the only sender that feeds water temp information to the monitor on that engine? My 56 had the sender much closer to the thermostat housing. Thanks for the help.

[JLR]

The fault can be in one of three places: The sensor can be bad, you could have a bad wire, or you could have a bad board.

Do as George describes to check the sensor. The same procedure can be done at the terminals on the board to check for a bad wire. If neither of the first two test solves the issue, then it is in the board itself.

Sky - I want to make sure I understand this. Just recently on my 74, I ran into a false water temp alarm. I pulled the two wires from the sender and jumped those and the alarm still sounded. Then I jumped the two wires on the board itself and the alarm was silenced. I thought that meant I had a bad board but I am pleased to read your analysis that jumping the board which stops the alarm means I have a bad wire, unless I read your post wrong.

[Canuck Dennis]

On my 6 71's the sender has only one terminal, odd that others have 2 ?. or, are there two senders, one alarm one temp reading ?

[SKYCHENEY]

Sky - I want to make sure I understand this. Just recently on my 74, I ran into a false water temp alarm. I pulled the two wires from the sender and jumped those and the alarm still sounded. Then I jumped the two wires on the board itself and the alarm was silenced. I thought that meant I had a bad board but I am pleased to read your analysis that jumping the board which stops the alarm means I have a bad wire, unless I read your post wrong.

Correct. Now try running a new wire from the board to the sensor. Don't bother tying it all up, just run it down the corridor temporarily to confirm that is your issue.