1997 Mazda Millennia has been running hot

You may have an internal coolant leak. It may not leak the coolant into the oil. You will need to run the following tests to determine if your problem is head or head gaskets: Remove all of the spark plugs. Pressurize the radiator with approximately fifteen pounds of pressure and wait for approximately thirty minutes to an hour then crank the engine over and watch to see if coolant comes out of the spark plug holes. This will tell you if your problem is a head gasket or possibly a cracked head. Also, check for exhaust gases in the cooling system with the engine running.