Recently bought a 2003 S-type Supercharged 4.2 V8 and while driving I had the engine light and "restricted performance" indicator lights come on and the thermostat needle went to 0. The car still ran but was sluggish. I called a Jaguar dealer to find out what to do and he told me I needed a new thermostat and thermostat housing. How do the thermostat and thermostat housing cause the "restricted performance" light to come on?