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boatdoc55

Advanced Contributor
"Hi Guys, Sterndrive mechanic

"Hi Guys, Sterndrive mechanic here and have a friends Mariner 50hp 4cycle at the shop. Dang buzzer is driving us nuts. constant scream so I know it's the heat side but this thing will run all day long at speed and down just off idle but when he goes to idle or trolling speed, 3 to 5 minutes later, SCREAM. It pisses like a race horse and has plenty of oil presure, checked with mechanical gauge. It will run on the hose all day. New impeller and T-stat. What gives???? Thanks"
 
"Could be a bad sensor itself

"Could be a bad sensor itself (or starting to go). These are just resistance driven - no resistance = horn. A cheap part (about 20 bucks) to replace.

Try just pulling the wires to it, if the buzzer stops you got the problem, otherwise maybe a bad buzzer (but check the oil sensor if equipped - they go with regularity as well)..."
 
"Doc, I did have a good look t

"Doc, I did have a good look through the service manual for this motor - must say that the information on the 4 strokes "lacks" quite a bit.

There is only a single paragraph even noting that there is an oil pressure sensor, and nothing to indicate the temp sensor.

It does however, show up on the wiring diagram but can only narrow it down to one of two things:
either a block tempurature switch (seems to be pretty much the same as a temp sensor in automotive applications that screws into the block) or a "thermo switch" (separate sensor).

Neither one is referenced or explained further in the manual (not that I can find).."
 
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