Temp Gauge Acting Strange

Boater420

Well-Known Member
Mar 11, 2015
1,259
Clearwater, FL
Boat Info
'97 330 Sundancer
V-Drives
Westerbeke 4.5BCG
Engines
Twin Merc 454's
I was out on the water last weekend and noticed my port temp gauge acting weird.

Started out fine, warmed up to 170 degrees, idled around for a while and all was good. Then rather abruptly, the gauge went to all the way to cold...slowly climbed back to 170 and repeated the process over and over.

It never climbed past 170, the raw water was warm coming out the exhaust, there was no signs of overheating. Everything was fine except the way the gauge was operating.

New bravo pump housing and impeller, circulating pump, thermostat and risers & manifolds last year. It's been acting fine otherwise.

Any ideas? Temp sending units? Gauge?
 
Sounds like a connection issue either at the sensor or the gauge... corroded or loose ground maybe.
 
Switch the wires on your gauges stbd for port and see if the problem follows the wires (or switch the gauges as that might be easier). Since the needle moved "abruptly" it sounds more like an electrical issue than a real issue.

Also check for dirty/loose connectors at the engine and gauge side.

Since it kept repeating itself, though, I'd lean towards a failing temp sender.
 
Switch the wires on your gauges stbd for port and see if the problem follows the wires (or switch the gauges as that might be easier). Since the needle moved "abruptly" it sounds more like an electrical issue than a real issue.

Also check for dirty/loose connectors at the engine and gauge side.

Since it kept repeating itself, though, I'd lean towards a failing temp sender.

I see two wires at the thermostat housing which look like sender wires. Are these both for the sender or is one for the system monitor?
 
one wire should be for the temp gauge and the other supplies the coolant temp to the engine ECM......

cliff
 
one wire should be for the temp gauge and the other supplies the coolant temp to the engine ECM......

cliff
Are the senders for each the same? Is there a way to tell which one is the temp gauge?
 
Are the senders for each the same? Is there a way to tell which one is the temp gauge?

For a 1 wire sensor:
Unplug one with the engine running. The temp gauge should go to cold. Ground that same wire and the temp gauge should go to hot.

For a 2 wire connector, temporarily shorting the 2 wires together should send the gauge to Hot.
 
Thank you guys, I'll be testing this weekend and post what happened.
 
"Typically"... the ALL tan wire will feed your gauge. The Tan w/Blue wire will be the overtemp alarm.
 
Oh, you can also switch the senders and see if the issue swaps to the other gauge.
 

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