[JimsCAL]

Yes, you want the recirculation water to bypass the heat exchanger. I wish the 5411 on my previous boat had the fresh water cooling. The raw water cooling was a pain for many years and eventually killed the engine.

I would consider going with a higher temperature thermostat. I find it hard to believe that an additional 20 degrees of water temperature would have any significant impact on the impeller life. The improvement in the operating conditions of the engine would seem to worth it. Impellers should be changed every year anyway.

 

[JimsCAL]

Yes, check for air in the system. Also double check that the hoses out of the thermostat housing are not swapped. That would cause the water to bypass the HX when the thermostat opens rather than sending it into the HX.

 

[JimsCAL]

It's acting as if the path from the t-stat housing to the HX is blocked, but I'm pretty sure it isn't.

Note that the thermostat would do this if the hoses were connected backwards. I am pretty sure the previous post saying the hose from the top of the thermostat housing should go to the HX inlet and the one from the bottom should go to the tee at the outlet. You should be able to tell where the water is going by feeling which hose is hotter when the engine first runs and comes up to temperature. The hose going to the tee should initially warm up first as the coolant is recirculating and the one going to the HX should be cooler. Then as the coolant heats up, the hose going to the HX should get hotter as the tstat opens and sends more water to the HX and less to the recirc.

 

[JimsCAL]

Sounds good! Only thing you seem to be concerned about is the temps running a bit low. May only be accuracy of the temperature gauge. In any case, its better than running the engine cold like you were before. If you can find a thermostat with a higher temperature rating (like 160 to 180F) that fits the housing, that would be even better.