Flexible engine metal warming system and method for an internal combustion engine

A system for optimizing fuel economy during an engine warm up phase of operation of an internal combustion engine, the system comprising:

• an exhaust manifold;
• a coolant pump that pumps coolant through the exhaust manifold;
• a temperature sensor that measures a temperature of coolant within the exhaust manifold;
• an engine control module that:
• prevents coolant flow through the exhaust manifold, an engine block portion of an engine, and a cylinder head portion of an engine;
• while coolant flow through the exhaust manifold, the engine block portion of the engine, and the cylinder head portion of the engine is prevented, determines an estimated temperature of the coolant in the exhaust manifold independently of the temperature of coolant measured by the temperature sensor;
• while coolant flow through the exhaust manifold, the engine block portion of the engine, and the cylinder head portion of the engine is prevented, determines whether the estimated temperature of the coolant within the exhaust manifold has reached a predetermined maximum threshold,
• wherein the predetermined maximum threshold is less than a temperature at which the coolant will begin to boil;
• when the estimated temperature of the coolant in the exhaust manifold has reached the predetermined maximum threshold, based on the temperature of the coolant measured by the temperature sensor, determines a minimum flow rate of the coolant through the exhaust manifold to maintain the temperature of the coolant at about the predetermined maximum threshold;
• and
• causes coolant flow through the exhaust manifold based on the minimum flow rate while continuing to prevent coolant flow through the engine block portion of the engine and the cylinder head portion of the engine.