Coolant — Types and Service
Coolant — Types and Service
Coolant — also called antifreeze — is a mixture of water and ethylene glycol or propylene glycol with additives that prevent corrosion, lubricate the water pump seal, and raise the boiling point while lowering the freezing point. Straight water boils at 212 degrees and freezes at 32 degrees. A proper coolant mixture — typically 50 percent coolant and 50 percent distilled water — raises the boiling point to over 260 degrees under pressure and lowers the freezing point to minus 34 degrees. The mixture ratio matters. Too much water and you lose freeze and boil protection. Too much concentrate and the coolant actually transfers heat less efficiently because water is the better heat carrier.
Coolant types — they are not interchangeable
Different manufacturers use different coolant formulations with different corrosion inhibitor packages. Green conventional coolant uses inorganic acid technology — IAT — and protects with a layer of silicate that coats the metal surfaces. Orange Dex-Cool uses organic acid technology — OAT — and protects by chemically bonding to the metal at corrosion sites without coating everything. Pink Asian formulas and blue European formulas use hybrid organic acid technology — HOAT — combining both approaches. These are not interchangeable. Mixing incompatible coolant types can cause the coolant to gel, form sludge, clog heater cores and radiator tubes, and accelerate corrosion instead of preventing it. Always use the exact coolant type specified by the manufacturer. Check the reservoir cap, the owner's manual, or the service data for the specification.
Coolant testing and service
Test coolant condition with a refractometer — it measures the freeze point by how light bends through the sample. A refractometer is more accurate than the old floating-ball testers. Test strips are also available that check pH and additive condition. Coolant degrades over time. The corrosion inhibitors get consumed. The pH changes. Old coolant becomes acidic and attacks the aluminum cylinder head, steel block, copper heater core, and rubber hoses from the inside. Coolant should be replaced at the manufacturer's recommended interval — typically every 30,000 miles for conventional green coolant and up to 100,000 miles for extended-life formulations. Extended life does not mean forever. When draining and refilling, always use distilled water — not tap water. Tap water contains minerals and chlorine that accelerate corrosion and leave scale deposits in the system.