Coolant Leak: Signs, Causes and How to Find It

A coolant leak shows up as a green, orange, pink or blue puddle with a sweet smell, a low coolant warning, steam, or an engine that runs hot. The most common sources are the radiator, hoses and clamps, the water pump, the thermostat housing and the heater core; leaks you cannot see, where coolant disappears with no puddle, often point to a head gasket. Find and fix it early, because running low on coolant overheats the engine.

Signs of a coolant leak

• Puddles under the front of the car, or crusty residue on hoses, the radiator or the engine
• A sweet smell from the engine bay or inside the car
• The coolant level dropping, or a low coolant warning
• The temperature gauge climbing; see engine overheating
• A wet passenger floor or foggy windows, which point to the heater core
• White exhaust smoke, which points to an internal leak; see exhaust smoke colors

Common causes

• Radiator: cracked plastic end tanks, corroded cores and leaking seams. A radiator leak often shows as crusty deposits on the core or tanks.
• Hoses and clamps: hoses harden and crack with age, and clamps loosen.
• Water pump: a drip from the weep hole means the seal is failing.
• Thermostat housing and gaskets.
• Heater core.
• Radiator cap: a weak cap lets coolant escape when hot.
• Head gasket or intake gasket: internal leaks that burn or mix coolant; see signs of a blown head gasket.

How to find a coolant leak

1. With the engine cold, check the level in the reservoir and radiator. Never open a hot radiator cap.
2. Look along the hoses, radiator, water pump and thermostat housing for wet spots or dried residue.
3. Use a cooling system pressure tester to pressurize the system and reveal slow leaks; UV dye helps find small ones.
4. If coolant disappears with no external leak, a combustion leak test can show whether exhaust gas is getting into the coolant.

How to flush a radiator

1. Let the engine cool completely, then drain the coolant from the radiator drain valve into a pan.
2. Refill with clean water, run the engine to operating temperature with the heater on, let it cool and drain again; repeat until it runs clear.
3. Refill with the coolant type and mix your owner’s manual specifies, and bleed air from the system as the manual describes.
4. Dispose of old coolant properly; it is toxic to people and animals.

Radiators we carry

For the C5, C6 and C7 Corvette we carry DeWitts radiators and radiator-and-fan combos, including shortened versions that make room for a front-mounted supercharger, and a SPAL fan. See them on our DeWitts page and our Corvette parts page.

More guides: oil in coolant · losing coolant but no leak · bad radiator symptoms.

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