Themostat misdiagnosis prevention method and engine system

A thermostat misdiagnosis prevention method, comprising:

• controlling an engine warm-up determination for an engine, and when the warm-up of the engine has been completed, controlling a thermostat fail determination entry by an engine load-based load cumulative air amount, and wherein controlling the thermostat fail determination by the confirmation of thermostat fail is performed by a monitoring ECU upon operation of an engine system;
• wherein controlling the thermostat fail determination entry divides a process of the monitoring ECU into high speed/high load and low speed/low load by engine information applied to the monitoring ECU;
• wherein controlling the thermostat fail determination entry includes:
• determining the load cumulative air amount by using a positive cumulative air amount according to the high speed/high load and a negative cumulative air amount according to the low speed/low load;
• and
• controlling the fail determination entry when the load cumulative air amount exceeds a specific value;
• and
• wherein the load cumulative air amount is calculated by a difference value between a corrected positive cumulative air amount and a corrected negative cumulative air amount, and the thermostat fail determination entry compares the difference value with a threshold.