The most common cause is a bad thermostat. You can purchase a
thermostat, gasket, and some blue rtv and do the job your self. After
the car has cooled, locate the thermostat housing, remove the bolts
and remove the housing. Remove the thermostat, and the old gasket.
Be sure to clean the surface thoroughly. If the surface of the housing
has corroded then that will need to be replaced as well. Assemble the
termostat, gasket, and housing using the blue rtv. Allow it to cure for
an hour at least. Add coolant and crank. Drive 30 miles, leave the car
running, check all hoses, hose ends, around the thermostat housing
and the water pump for signs of leaks. If you smell a sick sweet smell
then antifreeze is leaking out and burning. If the tailpipe has that sickly
sweet smell then you may have a warped head or blown head gasket.
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