Cars & Vehicles
Antifreeze and Engine Coolant
Radiators

When do you add coolant with the car started or not?

171819

Answer

User Avatar
Wiki User
01/10/2007

You should add coolant with the engine off and cool, top off the radiator and fill the coolant reservoir to the cool or cold level. When the system is hot or running it will be pressurized and will be dangerous to open. You can however add coolant to the overflow reservoir at any time.