Mariner 60hp thermostat

The high heat alarm has started going off at high revs on my 1995 Mariner 60hp 2 stroke. The impeller is only a year old and there is a very strong tell tale. I'm thinking the thermostat might be sticking. According to the parts diagrams, there are two types of thermostat - 120deg and 143 deg. Anyone know which one is used on which model? My serial# is OG196273.

I find that the smaller engines run the lower stat and the higher hp the higher. My son's 150 ran 143s as did my 2002 90 but my used, new to me a couple of years ago, 2002 115 had a 120.....somebody installed it. Beats me. All the engines ran fine at those temps and the stat is only used at speeds below 2500 RPMs when the poppet opens on larger engines. In colder climates and winter boating I would opt for the 143.

You didn't say under what conditions the alarm goes off. Also does your 60 have a poppet valve for higher RPM operation? Makes a difference. If poppet equipped, it opens at around 2500 RPMs. OT below would be stat related and above poppet related.

Yes it's a 60 with a poppet valve. Wasn't quite sure how that thing worked so that's great info, thanks. Alarm goes off after 10 mins at 4000. I can chug around all day with no problem at 2000. I've ordered a tstat kit which includes a new poppet so hopefully that will resolve the situation.