The auto manufactures (pushed by the EPA), want the best fuel economy possible or the least amount of emissions anyways. The most emissions emitted are when the engine is not at operating temperature. So the goal is to get that engine up to temperature as quickly as possible when you start it. When the engine is started, a richer fuel/air mix is used, thus a higher idle. The engine being the heat hog, doesn't want to heat up anymore coolant than necessary. The thermostat is closed at this point, restricting full circulation thereby heating the least amount of coolant and keeping the temperature in a rising situation. When the temperature reaches about 195 farenheit, the thermostat opens and allows coolant to start moving throughout the system. When the temperature reachs are 220 or so the coolant temperature sensor sends a signal to the computer and the fan kicks on bringing the temperature back down, thus preventing overheating.
At this point I think we should start evaulating the thermostat.
The knocking noise your hearing may be pinging, it is like a marbles rattling in a tin can. I agree with the possiblility of a mass air flow sensor problem. I waould gain access to it and spray the internal electrical portion of the sensor with Electrical cleaner, I'm not comfortable with anything else for that.
Thursday, September 13th, 2007 AT 7:34 PM