Thermostat

[carbob]

Last fall while in for other service I didn't feel comfortable doing myself, the mechanic read an error code (sorry I don't know the code number) described as the "second" stage of the thermostat on my M62 engine. He indicated the thermostat will only fail at this stage when the vehicle is driven hard- high RPM's. Since that time, driving normally I have noticed no issues related to cooling- heater works fine, temp gauge is normal, no drivability or starting issues. So I'm struggling with the need to replace it, the water pump was replaced for failure in 2016 and the thermostat was replaced prophylactically at that time and the thermostat was replaced again in 2016 because it failed. I flush the coolant about every 5-6 years. Appears my vehicle eats thermostats like tic tacs, does anyone have a similar experience and can anyone shed some light on this second stage of the thermostat's function?