Our starboard engine has been running a touch cooler than the port, so we pulled the thermostats to check them.
Heating them up in a pan of water showed them starting to open at 160 degrees F and fully open by 175. This seems normal, but we replaced them with spares anyway. Engine temps are from our mechanical Murphy gauges, so the senders are not likely wrong.
After installing the new t-stats, the engine still runs a little cooler than its brother, 165F compared to 175F with sea water temperature about 60F at cruise RPM.
Impellers are new on the raw water pumps, heat exchangers are clean.
Suggestions are welcome.