2008 Chevrolet HHR Owner's Manual - Page 284

How to Add Coolant to the Cooling System Notice: The engine has a specific cooling system drain and fill procedure. Failure to follow this procedure could cause the engine to overheat and be severely damaged. If the engine's cooling system needs to be drained and re-filled, please see the dealer/retailer. If no problem is found, but the coolant level in the coolant recovery tank is below the COLD FILL line, add a 50/50 mixture of clean, drinkable water and DEX-COOL® engine coolant at the coolant recovery tank. See Engine Coolant on page 5-24 for more information. If no coolant is visible in the coolant recovery tank, add coolant at the pressure cap as follows: {CAUTION: Steam and scalding liquids from a hot cooling system can blow out and burn you badly. They are under pressure, and if you turn the pressure cap - even a little - they can come out at high speed. Never turn the cap when the cooling system, including the pressure cap, is hot. Wait for the cooling system and pressure cap to cool if you ever have to turn the pressure cap. 5-30