Magazine for the auto service professional
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36 | April 2016 The Chassis degrees F (110 degrees C), as this tempera- ture level is conducive to good fuel economy, and better emissions, faster warm-up and better comfort for the operator inside the vehicle. But if the PCM decides from opera- tor input signals that a cooler engine temp of 185 degrees F (85 degrees C) is required for high speed or high load operation, a pulse width modu- lated heater circuit is actuated and the thermostat will open at a lower coolant temperature, allowing better performance. As soon as the PCM sees that those conditions have been removed (back to part throttle, exited off highway, etc.), the heater circuit con- trol slows current fow to the heater and the thermostat will go back to normal wax pellet operation and raise the actual set point back to 230 degrees F (110 degrees C), again improving the operating scenario. This in effect gives the PCM a number of operating modes that sets it apart from the standard three mode operation of the tradi- tional wax pellet thermostat. This temperature regulation happens unnoticed by the operator and can happen many times during a normal drive, but in the event that the thermostat goes bad, the wax pellet will still function as a fail safe and trouble codes will be set to alert the driver of the situation. One major advantage to the mapped thermostat design is that it doesn't take much to incorporate it into current engine strategies or architecture, and doesn't really require any major systems to be redesigned. But it will require the use of a scan tool to diagnose the system, since a mapped cooling system can set a number of codes and can be bidirectional controlled in some cases to make diagnostics easier. The use of an electrically controlled thermostat is not the only way that the cooling system can be mapped or controlled for better overall effciency. Ford uses an arrangement of control valves to control coolant fow on its 1.6L EcoBoost engines. The idea is to warm up the engine as fast as possible, reduce the internal engine operating friction and in turn lower emis- sions, and aid in heating the passenger compartment faster. This engine still uses a conventional wax pellet-designed thermo- stat and thermo-syphon cooling to cool Photo courtesy of the author. This shows the mapped thermostat connection and housing on a GM Malibu. The connection is behind the metal cover.