So I've been having this issue where my car has been fully warmed up to three bars (2001 AP1), and after few minutes of normal driving, the coolant temp gauge drops to two bars. It stays on two bars for 8-15 minutes, then goes back to three bars. This is in weather 50-79 degrees, under regular driving conditions. What would be the cause of this issue?

 

Stock radiator and thermostat?

 

Coolant temp sensor

 

The thermostat could be stuck open. If it gets too cold for too long you may get a CEL.