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In an exemplary embodiment, a method to control excessive temperature changes in a coolant circuit includes providing a coolant circuit including a bypass flow pathway bypassing a heat exchanger, said coolant circuit at an elevated operating temperature; providing an adjustable coolant flow through

In an exemplary embodiment, a method to control excessive temperature changes in a coolant circuit includes providing a coolant circuit including a bypass flow pathway bypassing a heat exchanger, said coolant circuit at an elevated operating temperature; providing an adjustable coolant flow through said bypass flow pathway and said heat exchanger; providing a coolant pump in said coolant circuit; determining a temperature change in said coolant circuit in response to initiating a coolant flow from said heat exchanger into said coolant circuit, said temperature change greater than a predetermined limit; and in response to said determined temperature change, adjusting at least one or more of said coolant pump speed and said coolant flow to maintain said coolant circuit within a predetermined temperature range.

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1. In a hybrid vehicle coolant circuit having a bypass flow pathway bypassing a heat exchanger, and a coolant pump providing an adjustable coolant flow divided between the bypass flow pathway and the heat exchanger, a method to control temperature changes in the coolant circuit comprising the steps

1. In a hybrid vehicle coolant circuit having a bypass flow pathway bypassing a heat exchanger, and a coolant pump providing an adjustable coolant flow divided between the bypass flow pathway and the heat exchanger, a method to control temperature changes in the coolant circuit comprising the steps of: providing an adjustable coolant split flow through said bypass flow pathway and said heat exchanger, said adjustable split flow adjusted to a predetermined coolant flow of said coolant divided between said bypass flow pathway and said radiator heat exchanger;calculating a predicted temperature change in the coolant circuit immediately downstream of said heat exchanger in response to initiating a coolant flow from the heat exchanger into the coolant circuit; andin response to the temperature change, adjusting at least one or more of a speed and a flow of the coolant pump to maintain the coolant circuit within a predetermined temperature range. 2. A method to control temperature changes in a vehicle coolant circuit having coolant, a heat exchanger bypass and a coolant pump with an adjustable speed and flow rate, and a heat exchanger, the method comprising the steps of: calculating a predicted coolant temperature change in the coolant circuit immediately downstream of said heat exchanger in response to initiating coolant flow from the heat exchanger into the coolant circuit; andadjusting at least one of the coolant pump speed and the coolant flow rate to maintain the coolant temperature within a predetermined temperature range if the coolant temperature change is greater than a predetermined temperature change limit;wherein said coolant flow is provided by a split flow valve, said split flow valve actively controlled by a preprogrammed controller in response to said temperature change, said split flow valve adjusted to a selected position to provide a predetermined coolant flow divided between said heat exchanger and said bypass. 3. The method of claim 2, wherein said coolant flow is provided by a split flow valve, said split flow valve passively controlled in response to coolant temperature. 4. The method of claim 2, wherein said coolant flow is provided by a split flow valve upstream and/or downstream of said heat exchanger, said split flow valve adjustable to adjust a flow of said coolant between said bypass flow pathway and said heat exchanger. 5. The method of claim 2, wherein said coolant pump speed is actively controlled by a preprogrammed controller in response to said temperature change. 6. The method of claim 2, wherein determining said temperature change comprises measuring a temperature of coolant within or exiting said heat exchanger. 7. The method of claim 2, wherein determining said temperature change comprises measuring a flow rate of coolant within or exiting said heat exchanger. 8. The method of claim 2, wherein controlling said pump speed comprises ramping coolant pump speed from a first speed to a second speed according to one of a continuously ramped rate or a series of stepped pump speed changes. 9. The method of claim 2, wherein controlling said coolant flow comprises adjusting a split flow valve position to limit flow though said heat exchanger wherein said coolant pump speed is one of constant over time or changing over time. 10. The method of claim 2, wherein said determining said temperature change comprises determining coolant flow resistance through portions of said coolant circuit including said heat exchanger and said bypass circuit. 11. The method of claim 2, wherein said determining said temperature change comprises determining said heat exchanger cooling rate and time said coolant is cooled in said heat exchanger. 12. The method of claim 2, wherein said determining said temperature change comprises determining ambient temperature. 13. The method of claim 2, wherein said determining said temperature change comprises monitoring a change in said coolant temperature with respect to time at a point downstream of said heat exchanger. 14. The method of claim 2, wherein said heat exchanger comprises a vehicle radiator. 15. A method to control excessive temperature changes in a vehicle coolant circuit comprising: providing a coolant circuit comprising a bypass flow pathway bypassing a heat exchanger, said coolant circuit at an elevated operating temperature;providing an adjustable coolant split flow through said bypass flow pathway and said heat exchanger, said adjustable split flow adjusted to a predetermined coolant flow of said coolant divided between said bypass flow pathway and said heat exchanger;providing a coolant pump in said coolant circuit;calculating a predicted temperature change in said coolant circuit immediately downstream of said heat exchanger in response to initiating a coolant flow from said heat exchanger into said coolant circuit, said temperature change greater than predetermined limit; andin response to said determined temperature change, adjusting at least one or more of said coolant pump speed and said split flow to maintain said coolant circuit within a predetermined temperature range. 16. The method of claim 15, determining said temperature change comprises measuring a temperature of coolant within or exiting said heat exchanger. 17. The method of claim 15, wherein determining said temperature change comprises measuring a flow rate of coolant within or exiting said heat exchanger. 18. The method of claim 15, wherein controlling said pump speed comprises ramping coolant pump speed from a first speed to a second speed according to one of a continuously ramped rate or a series of stepped pump speed changes. 19. The method of claim 15, wherein controlling said split flow comprises adjusting a split flow valve position to limit flow though said heat exchanger wherein said coolant pump speed is one of constant over time or changing over time.