The radiator of a Honda car contains a 50/50 mix of a glycol-based antifreeze/coolant and water. You can buy this pre-mixed from any auto parts store or your mechanic can use it. If you're using a pre-blended antifreeze, add it until full. If you're mixing it 50/50 with water, use distilled water instead of tap water to avoid scales forming in your radiator and heater core, and to ensure proper water pump lubrication. ^{kbb.com 1 2 3 4}