Al, For max power lower temps are fine. Most people find max power at around 175°F. Best efficiency is usually at slightly higher temp, around 190°F. With the modern need for higher gas milage most manufacturers are going to 190° thermostats. Having a too low temperature is something of a luxury though!
Bill Jepson

Bill;

Your last sentence is certainly true.  I put the 170F thermostat in-line with the second rad to keep the temp above that; thinking the one radiator in the cowl would not cool too much considering the added heat load from the oil/water cooler.  I drilled three 5/32” holes in the thermostat to keep some flow going through not thinking that would provide any significant cooling, but I guess it does.  First step is to replace the thermostat; then see if it might be appropriate to reduce the airflow into the in-cowl rad – in some way that reduces drag.  But the nice thing is there is no urgency – and my flight regime is not limited.

Al