2014 Mercruiser 4.3 TKS - intermittent false overheat alarm

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BC boater

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Hello all, This is my first post to the forum, I'll try to be as thorough as possible. First, the info:
2014 Larson LX195S - first owner
4.3 TKS (190)
Alpha 1
High Five 19P
75 hours
Used freshwater only - premium (94 octane) fuel
Problem: intermittent sounding of overheat alarm
Diagnosis progress so far:

Thanks to all the info elsewhere on this forum, I've learned a lot about this issue.
The alarm sounds intermittently when engine is at operating temp, and is a somewhat random pattern of beeps from the alarm - sometimes short blast, or series of varying duration beeps, sometimes longer steady... Occurs in calm or rough waters, when towing or cruising. Never at idle or slow speeds.
Disconnecting the sensor connector with the yellow and black wires at the base of the thermostat stops the alarm. Tried new sensor same problem. Gauge reads normal - never goes over 170, usually runs 160- 165. Verified temps with infrared thermometer, took readings several locations around thermostat (while duplicating operating conditions that would trigger the alarm) all normal, corresponds to gauge.
When alarm sounds, there is no drop in performance, engine always runs great, starts easily warm or cold, good power, smooth idle etc.
the boat is under warranty, but I'm reluctant to take it in - intermittent problem that will only occur under load at higher RPM 4000 to 4500. So, it will be hard to diagnose for the dealer. Besides, I don't mind spending a few bucks and fixing it myself, I prefer working on my own toys.

So, a couple of questions if I may: what else is on that sensor circuit? The wiring diagrams I have been able to find are pretty vague and appear to have some errors (ie incorrect sensor names, etc) is there anything else that is seeing the signal from the sensor enroute to the alarm that I should check? Are the latest manuals from Mercruiser better / more accurate than what's available for download online?
I should note TKS works normally with sensor disconnected. You can hear the sound of the air bypass when cold, quiets down as engine warms up. Idle speeds normal.
FYI I'm an old GM dealer tech, worked on these engines for years in light trucks and have been around cars and boats all my life. This engine is not overheating.
Any tips on testing these temp sensors in hot water? I tested the two I have (original and new one I bought) and both seem open until water is around 195. What ohm scale should I use for this test? Should they be open right up until they reach closing temp, then close, or do they show some gradual decreasing of resistance as they warm to the point there is enough current flow to set the alarm?

Any help would be appreciated, including suggestions for things I may have overlooked or different tests etc. I hate running around with that sensor disconnected - it's there for a reason.

Thanks all
 
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Fun Times

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What else is on that sensor circuit?
Hi there, Lately iboats forums has been getting similar type questions about the Carbureted engines sounding the warning horn for no apparent reason to the temperature circuit.

Thus far the unofficial fix has seemed to of been inspecting, disconnecting, cleaning, gently wiggling/pushing in the wire pins at the ICM connectors to ensure the associated wires/connectors are seated/making proper contact to the ICM. The yellow wire from the sensor mounted on the T/housing runs to the Ignition Control Module mounted on the port exhaust manifold riser. It's possible doing the above work may stop the horn.

Some past info regarding the horn and steps taken that seemed to help,
http://forums.iboats.com/forum/engi...944078-2004-mercruiser-4-3-intermittent-alarm
http://forums.iboats.com/forum/engi...rd-engines-outdrives/9934655-mercruiser-alarm

The wiring diagrams I have been able to find are pretty vague and appear to have some errors (ie incorrect sensor names, etc.) Are the latest manuals from Mercruiser better / more accurate than what's available for download online?
When it comes to the latest engine model wiring, Mercruiser decided to start using a Colored Wiring Diagram Binder for all their engines and when they did, they sent out a copy to all their dealers in turn eliminating the detailed engine wiring harness info inside the service manuals.

Let us know if this works for you as well...Good luck.
 

BC boater

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Wow. Fast reply - thanks Fun Times and the OPs who wrote about this. (Feeling dumb I couldn't find these posts on my own - have to work on my search skills...)
I'm going to plug in the sensor and run the boat to verify the intermittent alarm is still present, then disconnect, inspect and reinstall the wire connection at the ignition control module. Then retry to see if alarm stops sounding. I'll report back with the results. Tragically, I will have to wait until the weekend to get up to the lake to try this...
Thanks again guys.
 

BC boater

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Well,
Problem solved! Today, ran initially with sensor unplugged, no alarms of course. Stopped, re connected temp sensor, alarms started sounding within 5 minutes. Stopped, disconnected both connectors at the module, looked them over, saw nothing out of the ordinary, plugged them back in again and presto, no more alarms. Ran all day without a peep out of the alarm. Awesome. Thank you very much for this info.
Now, of course my inquiring mind wants to know how that alarm gets triggered thru that module, etc.
But for now, I'm just happy it's fixed. Iboats rules - thanks guys.
 

Fun Times

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Today, ran initially with sensor unplugged, no alarms of course. Stopped, re connected temp sensor, alarms started sounding within 5 minutes. Stopped, disconnected both connectors at the module, looked them over, saw nothing out of the ordinary, plugged them back in again and presto, no more alarms. Ran all day without a peep out of the alarm. Awesome. Thank you very much for this info.
Now, of course my inquiring mind wants to know how that alarm gets triggered thru that module, etc.
But for now, I'm just happy it's fixed. Iboats rules - thanks guys.
Too cool!!! & thanks for doing a full on water test of this theory that I came up with only by reading/trying to help many members with the same symptoms. I wish I could tell you exactly why this works but it was only a hunch of thinking what else could it be sounding the horn for no apparent reason with all other leads exhausted. Good job.:thumb:
 

ralphy670

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This was exactly my problem as well. It happened again this year and unplugging the connection at the module fixed it again. I wonder why this circuit runs through the module and what could be causing the issue.
 

nickmo

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Same here. I had an intermittent alarm for 2 years, saw the posts, unplugged the wire, re attached it and no more alarms. Thanks guys.
 

Kentucky32

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False alarm was driving me crazy as well. Changed manifolds and risers, thermostat, impeller along with sensors in thermostat housing, but still got false alarm. I disconnected wires on ECM and reconnected. Took on WOT ride and no alarm. It worked!!!
 
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