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Okay, here's the puzzler in as short a story as I can put it.
Bought a 1985 Montauk w/ a 1985 90HP 2 Stroke Yamaha (3 Cyl.). Before I bought it the owner had the engine overhauled and they installed a new thermostat to fix an overheat alarm problem.
The first day I ran it the overheat horn would go off at any RPM over about 3200.
We deduced it may need a water pump as the tattle tale was fairly week. We installed a new water pump kit (minus new upper and lower housings). We also installed a new thermostatic switch.
I ran the boat this weekend and noticed the tattle tale was much stronger and I was able to run the boat up to 4000 RPM with no alarm and it seemed definately better. At 4200 or so the alarm went off again.
While running the motor the tattle tale stream was barely luke warm to the touch but AFTER the motor was off and water was still drizzling out it felt very hot. (Note: No steam was observed coming off the motor)
Do I have a salted motor and will running it continually in fresh water eventually clean it out? Do I need to take the head apart and inspect the passage ways? Any ideas where I should go from here?
I believe that motor should cruise nicely at around 4500 RPM but maybe thats just too hard to run the old dog.
When changing out a water pump, it is very important to change the housing and plates on the pump as well (don't just change the impeller). The reason for this is that the plates wear down between where the impeller spins, and the metal plate touches. This may not look like much to the eye but, if you add up the wear on both plates (upper and lower) the gap is pretty big (enough to lose a considerable amt of water pressure). Hope this helps, take it from a salty "Long Island" kid, thats changed out lots of water pumps.
Roger that! We did change out the plates, seals, impeller and gaskets just not the actual lower oil housing and upper plastic water pump housing. Thinking of trying the Salt Away product and just running it in fresh water for now. Thanks!
Just to wrap up this thread... The engine is now cruising along at 4000 RPM and an indicated speed of about 30 - 33 MPH, i'm still yearning to push it up to 4500 but am not taking any chances of blowing it up. It seems like the continued running in fresh water is helping as I have not had any more overheat alarm (Knock on teak!).
