What Is Claimed Is:

1.

A four stroke internal combustion engine, comprising: a crankcase; a cylinder head connected to the crankcase, wherein the cylinder head and the crankcase together form at least one cylinder, and wherein the at least one cylinder includes at least one intake valve and at least one exhaust valve; a valve actuation assembly for operating the at least one intake valve and the at least one exhaust valve for the at least one cylinder; and a cooling system for cooling the engine, wherein the cooling system comprising a closed loop cooling system for cooling at least a portion of the engine having at least one coolant passageway extending around at least a portion of the at least one cylinder, wherein the coolant passageway is adapted to contain coolant to remove heat generated by the cylinder during operation, and an open loop cooling system for cooling at least a portion of the engine.

2.	The four stroke internal combustion engine according to claim 1, further comprising: an exhaust manifold for exhausting gas from the at least one cylinder, the exhaust manifold being connected to the cylinder head, wherein the open loop cooling system cools the exhaust manifold.

3.

The four stroke internal combustion engine according to claim 2, further comprising: a second exhaust manifold for exhausting gas from the at least one cylinder, wherein the second manifold is connected to the exhaust manifold and extends into a muffler system, wherein the open loop cooling system cools the second exhaust manifold.

4.	The four stroke internal combustion engine according to claim 3, wherein the first exhaust manifold includes a first open loop cooling passageway.

5.	The four stroke internal combustion engine according to claim 4, wherein the second exhaust manifold includes a second open loop cooling passageway.

6.	The four stroke internal combustion engine according to claim 5, wherein the second exhaust manifold and the muffler system are configured to prevent water from entering the cylinder head.

7.	The four stroke internal combustion engine according to claim 6, wherein the second exhaust manifold extends into a center portion of the muffler system.

8.	The four stroke internal combustion engine according to claim 6, wherein the second exhaust manifold includes a bend portion.

9.	The four stroke internal combustion engine according to claim 8, wherein the bend portion forms a gooseneck.

10.	The four stroke internal combustion engine according to claim 1, wherein the open loop cooling system includes an exhaust gas cooling assembly for cooling the exhaust gas as the exhaust gas enters the muffler system.

11.	The four stroke internal combustion engine according to claim 10, wherein the exhaust gas cooling assembly includes at least one cooling nozzle.

12.	The four stroke internal combustion engine according to claim 1, wherein each of the at least one coolant passageway includes a primary coolant inlet located at one end of the coolant passageway.

13.	The four stroke internal combustion engine according to claim 12, wherein each of the at least one coolant passageway includes a secondary coolant inlet located at an end of the coolant passageway opposite the primary coolant inlet.

14.	The four stroke internal combustion engine according to claim 1, wherein the at least one coolant passageway also extends through at least a portion of the cylinder head.

15.

The four stroke internal combustion engine according to claim 1, wherein the closed loop cooling system further comprises: at least one coolant pump for pumping the coolant through the at least one coolant passageway; and a heat exchanger for selectively removing heat from the coolant at predetermined engine operating conditions.

16.	The four stroke internal combustion engine according to claim 15, wherein a thermostat controls the operation of the heat exchanger.

17.	The four stroke internal combustion engine according to claim 16, wherein the heat exchanger is inactive when the temperature of one of the coolant and the engine is below a predetermined operating temperature.

18.	The four stroke internal combustion engine according to claim 16, wherein the heat exchanger is inactive during an engine startup operation.

19.	The four stroke internal combustion engine according to claim 15, further comprising: a lubrication system for providing lubricant to the engine; and at least one lubricant pump for pumping lubricant through the engine.

20.	The four stroke internal combustion engine according to claim 19, wherein the lubricant pump is operatively connected to the coolant pump.

21.	The four stroke internal combustion engine according to claim 20, further comprising: a lubricant cooler for cooling the lubricant in the lubrication system.

22.

The four stroke internal combustion engine according to claim 14, wherein the cylinder head comprises: at least one intake passageway operatively coupled to the at least one cylinder through the at least one intake valve; and at least one exhaust passageway operatively coupled to the at least one cylinder through the at least one exhaust valve.

23.	The four stroke internal combustion engine according to claim 22, wherein the coolant passageway in the cylinder head cools at least one of the intake passageway and the exhaust passageway.

24.	The four stroke internal combustion engine according to claim 22, further comprising: an air intake manifold connected to the cylinder head and operatively connected to the at least one intake passageway.

25.

The four stroke internal combustion engine according to claim 1, wherein the cylinder head comprises: at least one intake passageway operatively coupled to the at least one cylinder through the at least one intake valve ; and at least one exhaust passageway operatively coupled to the at least one cylinder through the at least one exhaust valve.

26.	The four stroke internal combustion engine according to claim 25, further comprising: an exhaust manifold connected to the cylinder head and operatively connected to the at least one exhaust passageway.

27.	The four stroke internal combustion engine according to claim 26, wherein the open loop cooling system comprises: an exhaust coolant passageway extending around at least a portion of the exhaust manifold.

28.	The four stroke internal combustion engine according to claim 27, wherein the exhaust manifold comprises: an inner manifold; and an outer manifold surrounding the inner manifold, wherein the inner manifold and the outer manifold are connected to one another to define the exhaust coolant passageway.

29.	The four stroke internal combustion engine according to claim 28, wherein the open loop cooling system comprises: at least one inlet port to permit coolant to enter the coolant passageway; and at least one exhaust port, permitting egress of coolant from the coolant passageway.

30.	The four stroke internal combustion engine according to claim 1, wherein the closed loop cooling system cools at least a portion of one of the crankcase and the cylinder head.

31.	The four stroke internal combustion engine according to claim 30, further comprising: an exhaust manifold for exhausting gas from the at least one cylinder, the exhaust manifold being connected to the cylinder head, wherein the open loop cooling system cools the exhaust gas.

32.	The four stroke internal combustion engine according to claim 31, further comprising: a lubrication system extending through the crankcase and the cylinder head, wherein the closed loop cooling system selectively cools the lubrication system.

33.

A personal watercraft, comprising: a hull; a seat assembly located on the hull and adapted to accommodate at least one passenger; and a four stroke internal combustion engine located within the hull, wherein the internal combustion engine comprises a crankcase secured to the hull, a cylinder head connected to the crankcase, wherein the cylinder head and the crankcase together form at least one cylinder, and wherein the at least one cylinder includes at least one intake valve and at least one exhaust valve; a valve actuation assembly for operating the at least one intake valve and the at least one exhaust valve for the at least one cylinder; and a cooling system for cooling the engine, wherein the cooling system comprising a closed loop cooling system for cooling at least a portion of the engine having at least one coolant passageway extending around at least a portion of the at least one cylinder, wherein the coolant passageway is adapted to contain coolant to remove heat generated by the. cylinder during operation, and an open loop cooling system for cooling at least a portion of the engine.

34.

The personal watercraft according to claim 33, wherein the closed loop cooling system comprises: a coolant flowing through at least one passageway in the crankcase and the cylinder head; at least one coolant pump for pumping the coolant through the at least one passageway; and a heat exchanger for selectively removing heat from the coolant at predetermined engine operating conditions.

35.	The personal watercraft according to claim 34, wherein a thermostat controls the operation of the heat exchanger.

36.	The personal watercraft according to claim 35, wherein the heat exchanger is inactive when the temperature of the coolant is below a predetermined operating temperature.

37.	The personal watercraft according to claim 36, wherein the heat exchanger is inactive during an engine startup operation.

38.

The personal watercraft according to claim 34, further comprising: a lubrication system for providing lubricant to the engine, wherein the lubrication system includes at least one lubricant pump for pumping lubricant through the engine, and wherein the lubricant pump is operatively connected to the coolant pump.

39.	The personal watercraft according to claim 38, further comprising: a lubricant cooler for cooling the lubricant in the lubrication system.

40.	The personal watercraft according to claim 34, wherein the coolant passageway extends through the crankcase and the cylinder head.

41.	The personal watercraft according to claim 40, wherein each of the at least one coolant passageway includes a primary coolant inlet located at one end of the coolant passageway.

42.	The personal watercraft according to claim 41, wherein each of the at least one coolant passageway includes a secondary coolant inlet located at an end of the coolant passageway opposite the primary coolant inlet.

43.

The personal watercraft according to claim 33, wherein the cylinder head comprises: at least one intake passageway operatively coupled to the at least one cylinder through the at least one intake valve; and at least one exhaust passageway operatively coupled to the at least one cylinder through the at least one exhaust valve.

44.	The personal watercraft according to claim 43, wherein the coolant passageway in the cylinder head cools at least one of the intake passageway and the exhaust passageway.

45.	The personal watercraft according to claim 43, further comprising: an air intake manifold connected to the cylinder head and operatively connected to the at least one intake passageway.

46.	The personal watercraft according to claim 33, wherein the closed loop cooling system includes a coolant flowing through at least one passageway in the crankcase and the cylinder head,.

47.	The personal watercraft according to claim 46, wherein each of the at least one coolant passageway includes a primary coolant inlet located at one end of the coolant passageway.

48.	The personal watercraft according to claim 47, wherein each of the at least one coolant passageway includes a secondary coolant inlet located at an end of the coolant passageway opposite the primary coolant inlet.

49.	The personal watercraft according to claim 46, wherein the closed loop cooling system further comprising: at least one pump for pumping the coolant through the at least one passageway; and a heat exchanger for selectively removing heat from the coolant at predetermined engine operating conditions.

50.	The personal watercraft according to claim 33, further comprising: an exhaust manifold for exhausting gas from the at least one cylinder, the exhaust manifold being connected to the cylinder head, wherein the open loop cooling system cools the exhaust manifold.

51.

The personal watercraft according to claim 50, further comprising: a second exhaust manifold for exhausting gas from the at least one cylinder, wherein the second manifold is connected to the exhaust manifold and extends into a muffler system, wherein the open loop cooling system cools the second exhaust manifold.

52.	The personal watercraft according to claim 51, wherein the exhaust manifold includes a first open loop cooling passageway.

53.	The personal watercraft according to claim 52, wherein the second exhaust manifold includes a second open loop cooling passageway.

54.	The personal watercraft according to claim 53, wherein the second exhaust manifold and the muffler system are configured to prevent water from entering the cylinder head.

55.	The personal watercraft according to claim 54, wherein the second exhaust manifold extends into a center portion of the muffler system.

56.	The personal watercraft according to claim 54, wherein the second exhaust manifold includes a bend portion.

57.	The personal watercraft according to claim 56, wherein the bend portion forms a gooseneck.

58.	The personal watercraft according to claim 51, wherein the open loop cooling system includes an exhaust gas cooling assembly for cooling the exhaust gas as the exhaust gas enters the muffler system.

59.	The personal watercraft according to claim 58, wherein the exhaust gas cooling assembly includes at least one cooling nozzle.

60.

A cooling system for an internal combustion engine, the internal combustion engine having a crankcase, a cylinder head connected to the crankcase, wherein the cylinder head and the crankcase together form at least one cylinder, wherein the at least one cylinder includes at least one intake valve and at least one exhaust valve, a valve actuation assembly, and an engine control system, the cooling system comprising: a closed loop cooling system for cooling at least a portion of the engine having at least one coolant passageway extending around at least a portion of the at least one cylinder, wherein the coolant passageway is adapted to contain coolant to remove heat generated by the cylinder during operation; and an open loop cooling system for cooling at least a portion of the engine.

61.	The cooling system according to claim 60, wherein the closed loop cooling system comprising: at least one coolant pump for pumping the coolant through the at least one passageway; and a heat exchanger for selectively removing heat from the coolant at predetermined engine operating conditions.

62.	The cooling system according to claim 61, wherein the heat exchanger is inactive when the temperature of one of the coolant and the engine is below a predetermined operating temperature.

63.	The cooling system according to claim 60, wherein the heat exchanger is inactive during an engine startup operation.

64.

The cooling system according to claim 60, wherein the engine further includes a lubrication system for providing lubricant to the engine, the lubrication system includes at least one lubricant pump for pumping lubricant through the engine, and the lubricant pump is operatively connected to the coolant pump, wherein the closed loop cooling system further comprises a lubricant cooler for cooling the lubricant in the lubrication system at predetermined engine operating condition.

65.

The cooling system according to claim 60, wherein the engine includes an exhaust manifold connected to the cylinder head and operatively connected to the at least one exhaust passageway, wherein the open loop cooling system comprises: a coolant passageway extending around at least a portion of the exhaust manifold; at least one inlet for receiving coolant from an external source through the coolant passageway; and at least one exhaust port.