Adaptive engine preheat

A preheat system for a diesel engine, said preheat system comprising:

• temperature sensor means for sensing the temperature of said engine and producing an output signal representing said temperature;
• an ignition switch;
• heater means for heating said engine;
• a programmable microprocessor, said programmable microprocessor including means for sampling said output signal when said ignition switch is turned on, calculating means for calculating a value representing an interval of time that said heater means must be energized to raise the temperature of said engine from the temperature represented by said sampled output signal to a desired temperature for starting said engine, and means responsive to said calculated value for energizing said heater means for said interval of time;
• said programmable microprocessor including a non-volatile memory in which is stored a parameter value S.sub.MAX representing a maximum interval of time said heater means may be continuously energized and a parameter M defining a relationship between time of heating and change in temperature of the engine during the time of heating, said calculating means being responsive to said parameter M and said sampled output signal for calculating said calculated value;
• and,
• said calculating means including means for comparing said value calculated from M and the sampled output signal with the parameter value S.sub.MAX and means for using the parameter value S.sub.MAX for energizing said heater means when S.sub.MAX is smaller than the value calculated from M and the sampled output signal.