Keep in mind that I am only a "shade tree" mechanic, but I do have some experience with this very problem...Take the radiator cap off and look in the filler neck with the engine running. BE CAREFUL!!! If you see bubbles sniff around the filler neck and see if it smells like exhaust gases...like burnt gas. If this is the case, the head gasket or the head itself is the culprit. Exhaust gases will blow passed the gasket/crack in the head and pressurize the cooling system. This pressure probably found a weak spot in the heater core and that would explain the steam. There may be other explanations but this is what happened to me today. When I identified the smell of exhaust gases coming from the radiator,it was evident that the problem was with the gasket/head.
Your transmission cooling tank is leaking into the radiator.Any oil in the cooling system will dramaticlly lower the cooling capabilities of your radiator.Replace rad. and flush coolig sys with cleaner.
Because it's leaking somewhere. Other than lines in the cooling system, head and intake manifold gaskets are a possibility.
Rust from your cooling system is flowing back into the overflow tank when the motor warms up.
Cooling system needs to be flushed - rust accumulation
Keep the overflow tank filled to its FULL line. Find the highest point in the cooling system; open it very slightly. Sometimes the highest point is the radiator cap. Sometimes the highest point is at a hose clamp. Very rarely there is a bolt that is meant to be loosened to let air out of the cooling system (example 1995 Mustang) You will hear air coming out. Keep filling the overflow tank. Then re-tighten the part that you opened. Also you will want to have the car's heater on HIGHEST/HOTTEST while doing this because the heater is connected to the cooling system.
Drain and flush your entire cooling system.
It does not necessarily indicate a problem. If the cooling system was over filled while cold, the excess will have to escape from the overflow when the pressure builds. This is normal. If it continues after several periods of the engine warming up, it may mean that the cap is defective.
You should not need to "bleed" it. The cooling system water pump circulates the coolant throughout the entire cooling system (including the cabin heater) and during the process any air in the system should migrate to the overflow tube and be exhauasted into the fluid overflow reservoir.
Not much, the excess coolant would be pushed out the overflow tube.
This is coolant. You have a leak in your cooling system or you water pump has failed and is leaking.
You have a leak in the cooling system. It could be from a number of sources such as, radiator, radiator hoses, heater core, heater hoses, water pump, intake manifold gaskets, head gaskets, cracked heads and probably a few more. Have the cooling system pressure tested to determine where it is leaking from and don't wait.
it has a bad head gaskit