Merc 115 overheating

[octaneforce]

My friend's 2003 2 stroke mercury 115 is overheating. After a minute or so of being on plane, the buzzer sounds and the water coming from the motor is very very hot. It will idle no problem and the exit water is cool, but under load it gets hot quick. Im not sure where to start. The water stream from the motor looks to be pissing strong. Does this thing have a thermostat?

 

[Schtoopid]

I don't have a shop manual, but I believe it has a thermostat.

 

[Texasmark]

Not the stat. That engine has a stat for speeds up to 2500 rpm. If your alarm goes off under that speed suspect it. Over that rpm (operator manual number) water pressure unseats a popoff valve that bypasses the stat and allows more free flowing water through the powerhead due to added heat due to higher rpms. Both are under a common cover on the rear of the engine block water jacket; probably upper left corner viewed from the rear of the engine.....that's where my 90 hp 3 cyl was located. Change both and while you are at it what's the condition of your impeller and have you ingested weeds lately? Do you operate in salt water?

 

[octaneforce]

Not the stat. That engine has a stat for speeds up to 2500 rpm. If your alarm goes off under that speed suspect it. Over that rpm (operator manual number) water pressure unseats a popoff valve that bypasses the stat and allows more free flowing water through the powerhead due to added heat due to higher rpms. Both are under a common cover on the rear of the engine block water jacket; probably upper left corner viewed from the rear of the engine.....that's where my 90 hp 3 cyl was located. Change both and while you are at it what's the condition of your impeller and have you ingested weeds lately? Do you operate in salt water?

Yes it operates in salt water and yes theres some weeds in the canal where the boat is kept. So yes i think the impeller should be done as well as the 2 parts you mentioned. However like i said the water pushes a nice stream from the outlet on the motor. Its a 4 cylinder also

 

[Texasmark]

The tell tale comes off the exhaust water jacket on the big plate on the port (left) side of the engine looking forward. That circuit is independent of the block water system due to the fact that exhaust has to be cooled as long as the engine is running. This may help in pointing to the pop off rather than clogging being the smoking gun. So, looking from here fix/look at the three things mentioned and you ought to be good to go. If the impeller is good as is, it will look like wagon wheel spokes and the tips won't be worn off, with no cracks anywhere. Fail any of the 3 items listed and you at least need a new impeller. If big enough groves to hook your finger nail in on the covers, you need a complete new pump assy. Iboats probably has your parts.