Re: 1990 115 Mariner alarm?
You have a low oil alarm and over temp. On some engines the low oil is intermitent. The OT is a solid note. On that engine the pee is plumbed off the exhaust manifold cover and really has nothing to do with the thermostat operating. All it does is to tell you that the water pump is pumping water to the powerhead. Same thing on my 3 cyl version of the engine....have the manual on both in front of me.
The engine has two temperature control mechanisms. 1st is the stat that starts to open at 143F or whatever is stamped on the bottom of the pellet that forms part of the stat. Full open will be 10-15F more.
Over 2500 rpm there is a flow bypass with a pressure resisting spring that opens and significantly increases the volume of water through the engine at the higher speeds, referred to as a popoff valve which is what it is. It swamps out the stat and basically renders it useless and it will be if the water temp is below the stat opening temp which would normally be the case.....boating in 143F water isn't for me.
I have had a frozen closed stat with a solid alarm sounding and would get up on plane and the alarm would squelch. As soon as I slowed back down, whenever that was, the alarm would sound again as the stat was in charge of engine temp and being stuck closed the internal water temp of the block exceeded the 195F closing temp of the OT sensor . That was my first outing with a newly purchased used boat.
After I got home I bought a new stat and that was the end of that.
HTH,
Mark
