1984 Mercury 200 Alarm at 5000 RPM

[JimSA]

I bought this '05 Pathfinder with very clean 200 Merc. The only problem is the over heat alarm (solid sound, no beeps) if I take it over 5000 (or 4900) for over a few seconds. When I come back to idle for a few seconds, the alarm goes away for good. It runs like a top at 4500, but there are times when I need the WOT. The water stream is steady and hot as soon as I start it. I apologize if this is a duplicate post, but I'm looking for a list of things that I should check out on my own before taking to a mechanic. Any feedback is greaty appreciated.

 

[JimSA]

Re: 1984 Mercury 200 Alarm at 5000 RPM

forgot to mention the compression checked out good on all cylinders (117-123) and I'm running a 4 blade trophy plus prop with 21 pitch.

 

[JimSA]

Re: 1984 Mercury 200 Alarm at 5000 RPM

from what I have read on this site, I should check the water pump, thermostats, poppet valve, and the alarm sensor. Any other ideas?

 

[JimSA]

Re: 1984 Mercury 200 Alarm at 5000 RPM

I just noticed that the spedometer guage hose was unplugged. I wonder if that is setting off a maximum speed sensor?

 

[j_martin]

Re: 1984 Mercury 200 Alarm at 5000 RPM

I just noticed that the spedometer guage hose was unplugged. I wonder if that is setting off a maximum speed sensor?

No, you don't have any fancy electronics on that engine. If WOT is only 5000 rpm, though, you might be overloading the engine and that alone would make it overheat.

 

[JimSA]

Re: 1984 Mercury 200 Alarm at 5000 RPM

No, you don't have any fancy electronics on that engine. If WOT is only 5000 rpm, though, you might be overloading the engine and that alone would make it overheat.

WOT is about 5600. Any other thoughts?

 

[JimSA]

Re: 1984 Mercury 200 Alarm at 5000 RPM

I also noticed some white foamy looking liquid around the thermostat on the starboard side. It looked like cloudy water but it was like a gel. Any idea what this is?