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Mercruiser Alarm

treeaxx

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"I have a 2001, 5.7L, Merc, Br

"I have a 2001, 5.7L, Merc, Bravo 3, I am getting an alarm from 2000-3000 RPM bringing the boat up to plane. I disconnected Gearlube low switch and still got the alarm, I disconnected oil pressure switch and still got alarm, I disconnected water temp. switch and alarm seems to go away. I replaced Engine temp. sender and switch and all looks good on the gauge (running around 140-160) BUT still getting the alarm between 2000-3000 RPM after hooking the engine switch back up. I borrowed a friends lazer temp reader and everything looks good, the engine, thermostat housing, exhaust manifolds and around the water temp sender and switch all read fine with the lazer temp reader....All readings anywhere from 140 to 160 degrees...After I unplugged water temp. switch and I don't get the alarm,, I ran the boat for 5-10 minutes on plane and friend took temp readings all over engine and it still looks fine (between 140-160)... Proactively I changed thermostat and took the old water temperature switch and performed boiling water test and the switch closed at 195 degrees....So at this point I am lost..Still getting alarm when I plug over temp switch in and my gauge says the engine is running fine and the switch closes electrically at 195 degrees..but still getting alarm between 2000-3000 RPMs.... Any ideas???"
 
"If you are a little low on co

"If you are a little low on cooling water flow you may be getting a short shot of hot water that trips the switch, but not enough to get high temp gun readings. If your sea water pump has not had a new impeller in a while, I would start there. You don't say where your water intake is, but if its a hull intake, might it be plugged, or is your intake strainer plugged? Kinked hose anywhere? Maybe your T'stat is getting sticky and not opening quickly enough? Cheap and easy to change.
Rod"
 
Sea Water pump is good..Water

Sea Water pump is good..Water intake comes into the thermostat housing..The problem is the gauges (including temp gauge on boat) are all reading correctly...Manifolds are also running normal...starting to wonder if there is corrosion or short in connection to water temp switch...I will update.
 
"Sounds like you're not ge

"Sounds like you're not getting enough cooling flow past the sending unit (temperature switch). I'm assuming from the description above you are raw water cooled.
A short in the temperature switch's wiring doesn't make sense, because the alarm goes away when you disconnect the wire from the switch, right?
If you tested the switch, and it closes at 195, and it reopens when it cools, you've pretty much proven that the temperature it's sensing when installed is greater than 195 after the engine warms up. There's a problem there somewhere, perhaps a blockage. I've seen one case where the tee fitting the switch threads into is so small that when the switch was threaded in, it just about completely blocked off the coolant flow."
 
UPDATE...I sodered 2 long wire

UPDATE...I sodered 2 long wires to the water overtemp switch and went for a ride. I could not get resistance measured across the switch. I then took my setup and did the boiling water test and the switch closed at 195 degrees and I measured resistance... This tells me the engine is not overheating and the problem is in the electrical system...maybe connection maybe something else.. and yes I agree if it shorts it would goto ground and the alarm should go off...So this is still a stumper...but I think I have eliminated an actual overtemp problem...
 
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