Q: Car keeps running hot even after i put in a new thermostat

The brown substance coming from the radiator may suggest a more serious problem, such as a blown had gasket. When this happens, the cylinder head gasket between the engine block and the cylinder head fails due to excessive heat. This will now allow oil to leak into the coolant passages inside the motor. This also causes water to leak into the combustion chamber of the engine causing it to be burnt with the fuel. You may notice a white smoke as well because of this. This is something that should be looked at as soon as possible by a professional such as one from YourMechanic. YourMechanic offers a repair and diagnosis service preformed by a certified mechanic that will commute to your location to inspect the head gasket.