Temperature Rise was only 2 deg/min
Below, in green, is the temperature rise at idle. The 160° thermostat that came with the engine starts opening at 145° and is fully open at 165°. The V6 Olds engine's cooling system gets to operating temperature in ten minutes at 12 deg/min (really nice on those 20 below mornings). It should also be noted that the Universal Service Manual from Westerbeke for M-30, M40, and M50 recommends an operating temperature of 165° to 195°, and the original Medalist Owner's Manual says it should be 170° to 185° F.
This slow rate of rise was true before and after moving the water heater to the thermostat by pass. The coolant going to the water heater is almost the same temperature as the water coming back.
The 180° thermostat is a NAPA 143 with no holes. This proved to make a nice difference in the rate of rise. Not only that, within an hour of running, the water is warm enough for me to take a short shower. The admiral has to wait for it to run a whole two hours before she'll jump into the shower.
