The consensus seems to be that the oil temp needs to be above about 80 centigrade when the motor is warmed up.
If it doesn't take too long to reach that after cold startup you may be ok, otherwise you may need a thermo.
BTW, where you locate the oil temp sender can affect the gauge readings.
I now have mine mounted in a sandwich plate under the oil filter to measure the oil just before it enters the motor. I originally had it mounted in the sump but the gauge read 10 degrees cooler, probably because of cooling air across the sender.