My sister drives a 2001 accord. She told me today that her cars heat doesnt work when shes on the highway. Says her engine temp is normal. When she does city driving she says the heat works but not very good. But once she gets on the highway the car doesnt blow anything but cold air. Since the temp gauge is reading normal I dont think it is a thermostat. Any ideas?

 

check the coolant level in the radiator and the overflow reservoir.