Engine cooling fan operation during hot soak

1. A method for an engine, comprising:

after an engine shutdown request is received, and while the engine is shut down, adjusting an engine cooling fan based on an engine temperature and an elevation of a fuel tank relative to the engine.

2. The method of claim 1 , wherein adjusting the engine cooling fan comprises powering the engine cooling fan in a reverse direction to blow air from the engine to outside the engine and away from the fuel tank.

3. The method of claim 2 , wherein adjusting the engine cooling fan based on engine temperature and the elevation of the fuel tank comprises adjusting the cooling fan in response to engine temperature being greater than a threshold and the elevation of the fuel tank being equal to or greater than an elevation of the engine.

4. The method of claim 3 , wherein the elevation of the fuel tank relative to the engine is determined based on an angle of a surface on which a vehicle is positioned, and wherein the engine and fuel tank are installed in the vehicle.

5. The method of claim 3 , further comprising, after the engine shutdown request is received and when the elevation of the fuel tank is lower than the elevation of the engine, not powering the engine cooling fan.

6. The method of claim 3 , further comprising, during engine operation, powering the engine cooling fan in a forward direction to blow ambient air to the engine.

7. The method of claim 2 , wherein powering the engine cooling fan in the reverse direction comprises de-energizing a first pair of transistors and energizing a second pair of transistors in a circuit of the engine cooling fan.

8. A method for a vehicle engine, comprising:

after an engine shutdown request is received, while the engine is shut down, powering an engine cooling fan to spin in a reverse direction from an engine operating direction responsive to engine temperature greater than a threshold temperature and an angle of a surface on which the vehicle is positioned less than or equal to a threshold angle, and not powering the fan when the angle of the surface is greater than the threshold angle.

9. The method of claim 8 , wherein powering the engine cooling fan to spin in a reverse direction in response to engine temperature greater than the threshold temperature and the angle of the surface, comprises, when the angle of the surface is less than or equal to a threshold angle, powering the engine cooling fan to spin in the reverse direction.

10. The method of claim 9 , wherein the threshold angle is zero.

11. The method of claim 8 , wherein powering the engine cooling fan to spin in a reverse direction in response to engine temperature greater than the threshold temperature and the angle of the surface comprises powering the engine cooling fan to spin in the reverse direction when engine temperature is above the threshold temperature and the angle of the surface is equal to or less than a threshold angle.

12. The method of claim 8 , further comprising, prior to receiving the engine shutdown request, powering the engine cooling fan to spin in the engine operating direction in response to vehicle speed being below a threshold vehicle speed.

13. A method for a vehicle comprising:

during engine operation, selectively operating an engine cooling fan with a forward spin direction; and

after an engine shutdown request is received, while the engine is shut down,

operating the engine cooling fan with a reverse spin direction when an engine temperature is greater than a threshold temperature; and

adjusting a speed of the engine cooling fan in the reverse spin direction as a function of an angle of a surface on which the vehicle is positioned.

14. The method of claim 13 , wherein adjusting the speed of the engine cooling fan in the reverse spin direction as a function of the angle of the surface comprises increasing the speed of the engine cooling fan in the reverse direction as the angle of the surface decreases.

15. The method of claim 13 , wherein adjusting the speed of the engine cooling fan in the reverse spin direction as a function of the angle of the surface comprises:

operating the engine cooling fan with the reverse spin direction at a first speed when engine temperature is greater than the threshold temperature and the angle of the surface is above a threshold angle; and

operating the engine cooling fan with the reverse spin direction at a second speed when engine temperature is greater than the threshold temperature and the angle of the surface is equal to or below the threshold angle.

16. The method of claim 15 , wherein the first speed is slower than the second speed, and wherein the threshold angle is zero.

17. The method of claim 13 , wherein selectively operating the engine cooling fan with the forward spin direction comprises operating the engine cooling fan with the forward spin direction in response to vehicle speed below a threshold speed, and wherein in the forward spin direction, the engine cooling fan is configured to direct ambient air from outside the vehicle toward an engine and fuel tank of the vehicle, and wherein in the reverse spin direction, the engine cooling fan is configured to direct air surrounding the fuel tank and engine to outside the vehicle.

18. The method of claim 13 , further comprising, after receiving the request to shut down the engine, determining if a leak detection test is to be performed, and when it is determined the leak detection test is to be performed, delaying operation of the engine cooling fan with the reverse spin direction until after the leak detection test is complete.

19. The method of claim 13 , further comprising, after receiving the request to shut down the engine, determining if a leak detection test is to be performed, and when it is determined the leak detection test is to be performed, adjusting a pressure threshold of the leak detection test based on the speed of the engine cooling fan.