How does thermostat work on 1991 Mercury 115 2+2 ?

[justchecking]

I ran it on the lake yesterday for the first time after the rebuild. I noticed that at idle the temp climbs to about 140F (I have a 143F thermostat and the water temp was about 55F).

At higher throttle (greater than about 1800 RPM) the temp drops down to 100F.

Is the poppit valve opening or something? How is it designed to work?

All the parts are new and the poppit spring has the same force as the original.

 

[oldman570]

Re: How does thermostat work on 1991 Mercury 115 2+2 ?

It sounds as like the thermostat is working as it should. The poppet valve is opening and is allowing more water flow at higher RPM's as it should. The poppet valve opens because of the water pressure and not so much as the water temp of the motor. Sounds like everything is operating as it should. JMO
Oldman570

 

[Texasmark]

Re: How does thermostat work on 1991 Mercury 115 2+2 ?

The pellet on the stat is stamped 143F with a tolerance of about 5F both ways. It controls the cooling up to around 2500 rpm. At that point water pressure is sufficient to unseat a much larger valve (poppet) allowing for unobstructed flow at a much larger volume. With the water at 55F the stat probably will not get hot enough to open so all the flow is through the poppet. At the higher rpms, the cooling requirement is obviously larger and at higher rpms you don't need a stat.

HTH,
Mark

 

[CharlieB]

Re: How does thermostat work on 1991 Mercury 115 2+2 ?

System working perfectly.

 

[justchecking]

Re: How does thermostat work on 1991 Mercury 115 2+2 ?

Great! Happy to hear it's working normally. My other motor is a 1984 115 6 cyl without a thermostat, so didn't know how they work in an outboard.
Thanks for the replies....