E28+ cooling question

[Alsail]

Hi everyone; E28+ (first season that I have the boat) here with the 5411 direct raw water cooled. Engine runs fine, but cold; turns out that the previous owner had completely closed (shut off valve) the return and so the thermostat was never recirculating to get the temp up. Engine temps were around 100F (but again, running smoothly, no issues). When I opened the return and replaced the thermostat (also has new raw water pump) the engine comes up nicely to 140-150F and stays there, so all good. Just that it seems that even at full speed there is significant recirculation needed to keep the engine temp up, which in turn reduces the water flow into the exhaust, with the result that quite a bit of steam is generated out the exhaust (and the exhaust water is on the warmer side). Anybody have any idea what is going on? - if I restrict the return I get the exhaust to stop steaming, but then the engine temp drops. If I run the engine temps at the correct temp I get steam. Almost looks to me like the cooling system is overdimensioned for the engine?
Thanks for any advice ...
Best
Alex
E28+, Maine.

 

[Kenneth K]

The Universal manual says 135-155F is the correct temp for the M-15/5411 so it sounds like you are right in there.

If all the water is recirculated (thermostat closed) to keep the engine at that temp, then it seems the steaming would eventually stop when all the existing water and vapor in the exhaust has dried up. At this point you would have a "dry" exhaust system which would be expected to result in hotter hoses than a "wet" system. No danger to the engine (which should be kept at 135-155F, and not 100F), but may be harmful to the muffler and exhaust hoses.

In a fresh-water cooled system (like the M-25) a raw-water pump is always pumping raw water through the heat exchanger and exhaust system whether the thermostat is opened or closed. Don't know if you RWC engine is designed the same way.