Had been on vacation and my 2007 H2 was standing for more than 2 months. Now when i drove for few kilometers and stopped, the complete coolant was boiling and overflowing theough the excess pipe. I refilled with fresh new 6ltrs of coolant but same thing happened again after i reached home. Any analysis why it could happen? What grade of coolant should i look at to buy? Should i fill the coolant while engine running or stopped? How much coolant should i fill??