2000 Mercury 175 EFI False overheat horn

[mpsergeantmajor]

I've been chasing this overheat horn thing since May. So far I've spent about $800 bucks and two different factory trained guys, only to be told that there's nothing that can be done because motors are leaned these days to cut down on emissions (2000 motor) so it's gonna happen from time to time...that's unacceptable to me. Will typically do it once a day; I shut it down and it starts right back up (no horn) and runs fine. All the sensors check out good, new impeller (w/p strong), and everything is oiling correctly. Temperature at idle is 185/190. I'm pissed!
Has anyone else had this problem and solved it?

 

[gss036]

Re: 2000 Mercury 175 EFI False overheat horn

The thermostats should be 143 degrees. If you are getting good circulation and the poppet valve is closed as it should be at idle, then the temp should be somewhere in the 143-160 degree range.
My next question is, are you using the motor for trolling at slow speeds for long periods of time?

 

[JUSTINTIME]

Re: 2000 Mercury 175 EFI False overheat horn

sounds like poppet or t-stats are even clogged passage ways
find a new shop

 

[mpsergeantmajor]

Re: 2000 Mercury 175 EFI False overheat horn

Thanks, I am changing Mechanics. Running when the horn sounds. Idles rough right now. Hopefully the new mechanic here in the Atlanta area can run it down.

 

[Texasmark]

Re: 2000 Mercury 175 EFI False overheat horn

195F should be the setting for your alarm sensor....give or take a few degrees for component tolerances. Like gss said, 143F on the stat so temp should be there or surely not more than 10 degrees higher. Sounds like your protection circuit is doing it's job.

So, sounds to me like you have internal circulation problems which don't allow your engine coolant to circulate properly.

Mark