2003 Mercury 115 2 Stroke Warning Alarm

[SteveDee2]

Hey Guys,
Hopefully someone can point in the right direction. I have a low hour 2003 115hp, today on the water at about 4000 RPM the warming alarm started sounding and stayed on. I brought it down to neutral and it went away. Same thing happened a few times anytime I got it up to speed.

Motor didn't appear to be running hot, I removed the cover and the head felt hot but not overheated, the water stream spraying out was constant and warm to the touch, not super hot.

Motor appeared to be running fine, no strange sounds or anything.

Any ideas of what to check next?

 

[Texasmark]

Cooling has 2 circuits:

1. Thermostat controlled, 143F opening temp, good to 2500 rpm (maint. manual rpm number). Under the same cover, on the top left rear of the engine block is the poppet valve that opens on water pressure which occurs at around 2500 rpm bypassing the smaller opening thermostat and allowing a higher volume of non temp controlled water to flow. The OT sensor, tan or tan with lt. blue stripe single wire connected to it, also mounted on the rear of the engine block shorts out to ground, battery negative, at 195F. If you have a US domestic hot water heater in your home and have the temp set to Normal, the average value of the heat of that water is 140F for a number as to what normal feels like on the engine.

Your water pump is a centrifugal design and the vanes (look like the spokes of a wagon wheel, made of flexible rubber) bend back at high rpms depending mainly on ram water input from the row of holes on the sides of the LU just ahead of the prop. Personally I look for water pump problems at lower speeds where there is no ram water to speak of and the impeller vanes aren't straight any longer but bent back and can't seal to the walls of the water pump and pull in adequate water.

So if you are having as you say, problems at higher speeds, you could still have a bad impeller in your water pump blocking flow, but you could also have corrosion in the engine's water jacket, an impeller blade broken off and blocking off flow, or engine mounted too high, too high of a trim angle, pinched wires in your OT sense wiring, or a bad OT module. If you have the module OT is a solid short and low oil is a 101010101. If you don't have the module, there is nothing to modulate the oil fault and they both will be solid alarms.