I have a 2000 740IL with 40,000 miles which we just purchased. We have driven it about 1,000 miles on two long trips and suddenly last night it over heated after going about 5 miles. The coolant was extremely low so I filled it back up. Now the thermostat gauge goes right to red when I start the car. Any idea what is wrong?

How much time elapsed between adding coolant and restarting the engine?

I would check for a coolant leak somewhere if I were you.

After I posted I did find a leak, but even after 12 hours and with new coolant the thermostat still pegs over red. BMW now has the car because it has a crack down one side of the radiator and they should fix the gauge also. Thanks!!

the gauge goes to red until the faults are cleared. then it will return to normal operation.