This study aimed to evaluate the impact of the duration of idling on engine warm-up and engine cool-down, and to assess the effectiveness of an energy recovery system. The results confirmed that there is no need to idle an engine for extended periods after a cold start to warm it up. It is more efficient to idle the engine for a short period, and then drive the vehicle or operate the machinery at moderate loads until the engine warms up to normal operating temperatures. The tests also confirmed that the engine retains enough heat for easy starting even after being shut down for a few hours and there is no need to idle an engine for fear of having cold start problems. The tests with an energy recovery system, which circulates engine coolant to the heater after the engine is shut down, showed that the system can maintain cab temperatures at comfortable levels even after the engine has been shut down for a few hours. This product would be ideal for day cab applications where idle periods rarely exceed one or two hours, or on heavy equipment that currently do not employ anti-idle technologies. The series of tests were performed were on a truck engine, yet the results can be applied to most diesel engines in trucks and heavy machinery.