Temperature control system for internal combustion engine

A temperature control system for an internal combustion engine, to which a block heater for warming a coolant and keeping the coolant warm is attachable, the temperature control system comprising:

• a coolant circulating apparatus configured so as to circulate the coolant;
• a fluid temperature detecting device configured so as to detect a fluid temperature of the coolant;
• a block heater disuse estimating portion configured so as to estimate a possibility of disuse of the block heater under a condition that a circulation of the coolant is stopped;
• and
• a block heater usage determining portion configured so as to determine whether or not the block heater is used on the basis of changes in the fluid temperature under a condition that the coolant is circulated in a case where the block heater disuse estimating portion does not estimate the disuse of the block heater.