At what temp should an overheat alarm sound?

[Aviator04]

I was running my 90 2stroke today at cruise speeds and the alarm went off. My temp gauge was showing around 135 degrees. Tell tale stream was relatively cool to the touch. Cylinder head was pretty warm but I don’t think I’d call it hot. I don’t think I was over heating, but I do believe the thermostats in these 3 cyl motors is 120 degrees, so maybe it was running slightly warm? I’m thinking I may have a bad temp alarm sensor. Does anyone know for sure what temp the alarm is supposed to go off at? I actually called mercury themselves and amazingly the guy I spoke to didn’t have an answer. I just want to determine if It was actually running too hot or not. Thanks!!

 

[Texasmark]

190F give or take a few percent tolerance for alarm to sound, 170F to cease. Tstat opening temp in my 2002 3 cyl 90 was 143F.

I have since bought a 115 4 cyl of that series and it came with a 100F stat. Looking up in the parts list I got a 125F as I wanted it to run a little hotter, but this is a 2+2 engine and has an RPM limiter at 5250....a different design even though it's a 4 cyl version of the 90 triple.

I have installed a cylinder thermometer, dash readout and with a stat running below about 2500 rpms the stat holds the temp really well at the opening temp. Once you accelerate above that RPM, water pressure unseats the poppet valve (both engines have one) which has a much larger volume capacity and bypasses the tstat. My 115, when cruising with the poppet open runs about 50F above ambient water...as detected by the thermometer on my depth finder. I would assume the 90 would run around that temp also above 2500 rpms..

 

[GA_Boater]

Since you don't say what motor other than "90 2stroke", could the alarm be for something other than an overheat?

 

[QBhoy]

Real good chance your alarm is for low oil injection level ? Amongst a few other things ?

 

[Aviator04]

Since you don't say what motor other than "90 2stroke", could the alarm be for something other than an overheat?

It’s a 2006 90 elpto carb’d. Solid continuous alarm on these is overheat. The Other alarm is for low oil but Is short individual beeps

 

[Aviator04]

190F give or take a few percent tolerance for alarm to sound, 170F to cease. Tstat opening temp in my 2002 3 cyl 90 was 143F.

I have since bought a 115 4 cyl of that series and it came with a 100F stat. Looking up in the parts list I got a 125F as I wanted it to run a little hotter, but this is a 2+2 engine and has an RPM limiter at 5250....a different design even though it's a 4 cyl version of the 90 triple.

I have installed a cylinder thermometer, dash readout and with a stat running below about 2500 rpms the stat holds the temp really well at the opening temp. Once you accelerate above that RPM, water pressure unseats the poppet valve (both engines have one) which has a much larger volume capacity and bypasses the tstat. My 115, when cruising with the poppet open runs about 50F above ambient water...as detected by the thermometer on my depth finder. I would assume the 90 would run around that temp also above 2500 rpms..

I wonder why they used different temp thermostats in different years. My 90 and your old 90 are only 4 years apart and the same exact engine. Mercury told me today 120 degrees is the correct one for my engine.. but there’s def no way this motor got up to 190.. I’m going to replace the alarm sensor, it had to bad. Out of curiosity, do you ever hear of poppet valves going bad? Put in a new spare t-stat i had today but didn’t even think to check the poppet..

 

[Texasmark]

Since you don't say what motor other than "90 2stroke", could the alarm be for something other than an overheat?

Low oil level in the tank will beep also but they are distinguished by solid vs pulsating. The oil is a warning so it pulsates when the engine mounted tank gets down to about a quart. The OT is solid and tells you time to take action.....NOW!

Edit: Oops, just saw that Aviator had already answered this.