If I had to guess, I would say the two things are not related. Are you sure the coolant is full? Also, when the engine is running, hot, and the heater on high, are both heater core hoses hot? Finally, has the coolant ever boiled over?
As far as the speedo, it sounds like there is a problem with the vehicle speed sensor (VSS). It is the sensor that tells the speedo how fast the car is moving. Many times it will set a "Check Engine" light. Has that ever happened?
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Saturday, December 5th, 2009 AT 7:23 PM