Engine Temp Sensor Going Off

Searayguy185

Member
Jul 17, 2017
87
Wisconsin
Boat Info
2004 Sea Ray 185 Sport 4.3 V6,

2008 Toyota Highlander Sport
Engines
Mercruiser 4.3 V6, Alpha 1 Generation 2
So i've had this problem for about a year now and it's driving me crazy. First off I have a 2004 Sea Ray 185 with the 4.3 carb engine. When I'm putting around under 3000 RPM'S everything all good. As soon as I start running hard one 3000 RPM'S It will chirp the alarm. Not a constant alarm but either one or two beeps. I disconnected the sensor harness under the thermostat to see if i could narrow the problem down. I used it for 3 months with no problems what so ever, so i knew it was coming from the temp sensor. Logically I replaced the temp sensor with a new one from amazon. Same part number as what the Mercury tech support gave me. Plugged it in and again started to beep. Engine is running a little over 170 at the hottest. I have no idea what to think at this point moving forward. Any thoughts.
 
Have you pulled the thermostat housing and checked the thermostat gasket? It has two little brass rivets in it that allow the top part of the housing to ground to the bottom part. If this connection is bad it will make the temp gauge and sensor act funny. It has nothing to do with the actual cooling, but can make the gauge ready wrong and potentially cause the sensor to read wrong also. It's worth the 10min it will take to ensure that gasket is in good shape and grounded.
 
Ditto to what Bill said. Although, I would "think" that if the brass nibs weren't making contact that it would be the same as disconnecting the sensor. I would also look for obstructions (old impeller piece?) in the thermostat housing. Look real close into all of the nooks and crannies. If there's an obstruction, that can disrupt water flow and cause an air pocket - which heats up much faster and hotter, causing the alarm. As soon as the cool water hits the sensor again, the alarm goes off.
 

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