1. Check water pump first, If leaks, change it immediatly. Otherwise it will be seized, then break the t-belt, then it will damage your engine within 10 seconds.
2. Check your cooling system hoses.
3. Check your expansion tank cap.
4. Check your heater.
5. Check the bleeder screws.
6. Check the oil cooler.
7. Check the bypass.
8. If all above is ok, you shold check the head gasket. It is very difficult and expensive to change.
Good Luck!
