Why is there the smell of oil when I turn on my heater in the car?

It is quite strong. Is this likely to be due to a head gasket fault, allowing oil into the water.Why is there the smell of oil when I turn on my heater in the car?
quite often it is an external oil leak from your engine.Why is there the smell of oil when I turn on my heater in the car?
look at your engine there may be a leak in the head gasket allowing oil onto your headers which in turn is creating that smell when you turn your heater on because that is where your hot air is funneled from
probably the heater core going bad, when the defrosters are on do the windows steam up?, if so you need a new heater core.