Recently my engine
has started to run hot when under load (temp creeping over 190 to 200). If I throttle back to less than 1100 RPM's the temp comes down to around 160-180. Even running in gear
at the dock
at 1400 RPM
(which gets me about 7 knots of speed on my 42' steel
sloop) and the temp does not climb about 160 or so. The bottom and prop are clean and nothing has been changed.
I changed the raw water
impeller (the old one was worn but had all the blades), and have gone through the raw water
system checking for flow and blockages. It appears fine all the way through to where it exits the boat, and water
flow out the back seems good. However, I am told the riser should be cool to the touch if raw water
flow is adequate - mine is quiet warm but I can keep my hand on it easily.
Wondering if it could be the closed system? Do these water pumps fail? What about the thermostat maybe only opening partially? I am not losing cooling
fluid, though I find it strange that I can open the filler cap without any pressure build up even when the engine
is up to temperature.
Thanks in advance for you advice and help!