Thermostat monitoring system and method

1. A thermostat monitoring method, comprising:

measuring an engine coolant temperature with an engine coolant temperature sensor a predetermined amount of time after engine startup;

comparing, with a controller, the engine coolant temperature to determine whether the engine coolant temperature has met a predetermined threshold;

when the engine coolant temperature has met the predetermined threshold, measuring a plurality of engine coolant temperatures with the engine coolant temperature sensor;

comparing with the controller each of the plurality of engine coolant temperatures with a corresponding predetermined temperature model;

increasing a passing index with the controller for each of the plurality of engine coolant temperatures that is greater than the corresponding predetermined temperature model and reducing the passing index for each of the plurality of engine coolant temperatures that is less than the corresponding predetermined temperature model; and

determining with the controller whether the thermostat has failed previously, when the controller determines that the thermostat has failed previously a first increment is used for the increasing, and when the controller determines that the thermostat has not failed previously a second increment is used for the increasing, the second increment being different from the first increment.

2. The method of claim 1 , further comprising

when a predetermined number of each of the plurality of engine coolant temperatures is greater than the corresponding predetermined temperature model, determining that the thermostat has passed.

3. The method of claim 2 , further comprising

resetting a pass/fail counter.

4. The method of claim 1 , further comprising

when a predetermined number of each of the plurality of engine coolant temperatures is less than the corresponding predetermined temperature model, determining that the thermostat has failed.

5. The method of claim 4 , further comprising

resetting a pass/fail counter.

6. The method of claim 1 , wherein

when at least some of the plurality of engine coolant temperatures are determined to be below a second predetermined threshold determining that the thermostat has failed.

7. The method of claim 1 , wherein

when at least some of the plurality of engine coolant temperatures are determined to be above a second predetermined threshold determining that the thermostat has passed.

8. A thermostat monitoring system, comprising:

an engine coolant temperature sensor configured to measure an engine coolant temperature a predetermined amount of time after engine startup;

a controller programmed to compare the engine coolant temperature to determine whether the engine coolant temperature has met a predetermined threshold, when the controller has determined that the engine coolant temperature has met the predetermined threshold, the controller is programmed to cause the engine coolant temperature sensor to measure a plurality of engine coolant temperatures, and the controller further programmed to compare each of the plurality of engine coolant temperatures with a corresponding predetermined temperature model, and increase a passing index for each of the plurality of engine coolant temperatures that is greater than the corresponding predetermined temperature model and reduce the passing index for each of the plurality of engine coolant temperatures that is less than the corresponding predetermined temperature model, when the controller determines that the plurality of engine coolant temperatures is less than the corresponding predetermined temperature model, the controller is programmed to reduce the passing index by a first predetermined increment, and when the controller determines that the plurality of engine coolant temperatures is less than the corresponding predetermined temperature model and a vehicle speed is less than a threshold vehicle speed, the controller is programmed to reduce the passing index by a second predetermined increment different from the first predetermined increment; and

a storage device configured to store the passing index.

9. The system of claim 8 , wherein

the controller is programmed to determine the thermostat has failed when a predetermined number of each of the plurality of engine coolant temperatures is less than the corresponding predetermined temperature model and cause a fail indicator to be activated.

10. The system of claim 8 , wherein

the controller is programmed to determine the thermostat has failed when at least some of the plurality of engine coolant temperatures are determined to be below a second predetermined threshold and cause a fail indicator to be activated.

11. A thermostat monitoring system, comprising:

an engine coolant temperature sensor configured to measure an engine coolant temperature a predetermined amount of time after engine startup;

a controller programmed to compare the engine coolant temperature to determine whether the engine coolant temperature has met a predetermined threshold, when the controller has determined that the engine coolant temperature has met the predetermined threshold, the controller is programmed to cause the engine coolant temperature sensor to measure a plurality of engine coolant temperatures, and the controller further programmed to compare each of the plurality of engine coolant temperatures with a corresponding predetermined temperature model, increase a passing index for each of the plurality of engine coolant temperatures that is greater than the corresponding predetermined temperature model and reduce the passing index for each of the plurality of engine coolant temperatures that is less than the corresponding predetermined temperature model and determine whether the thermostat has failed previously, when the controller has determined that the thermostat has failed previously, the controller is programmed to use a first increment for increasing the passing index, and when the controller has determined that the thermostat has not failed previously the controller is programmed to use a second increment for increasing the passing index, the second increment being different from the first increment; and

a storage device configured to store the passing index.

12. A thermostat monitoring system, comprising:

an engine coolant temperature sensor configured to measure an engine coolant temperature a predetermined amount of time after engine startup;

a controller programmed to compare the engine coolant temperature to determine whether the engine coolant temperature has met a predetermined threshold, when the controller has determined that the engine coolant temperature has met the predetermined threshold, the controller is programmed to cause the engine coolant temperature sensor to measure a plurality of engine coolant temperatures, and the controller further programmed to compare each of the plurality of engine coolant temperatures with a corresponding predetermined temperature model, and increase a passing index for each of the plurality of engine coolant temperatures that is greater than the corresponding predetermined temperature model or reduce the passing index for each of the plurality of engine coolant temperatures that is less than the corresponding predetermined temperature model, and when the controller determines that the plurality of engine coolant temperatures is less than the corresponding predetermined temperature model, the controller is programmed to reduce the passing index by a first predetermined increment, and when the controller determines that the plurality of engine coolant temperatures is less than the corresponding predetermined temperature model and a vehicle speed is less than a threshold vehicle speed, the controller is programmed to reduce the passing index by a second predetermined increment different from the first predetermined increment; and

a storage device configured to store the passing index.