Coolant Leak
Coolant leaks range from a loose hose clamp (a five-minute fix) to a blown head gasket (a $1,500 repair). Finding the leak source early makes all the difference in repair cost.
Can I Drive?
Yes, if the level is still acceptable — but top off and monitor daily. If you can smell coolant burning or see white exhaust smoke, stop driving immediately — internal engine damage is imminent.
Most Likely Causes
- 1
Leaking radiator hose
Rubber hoses crack, swell, or develop pinholes over time. The most common external coolant leak. Look for dried coolant residue (white or rusty stain) near hose ends and clamps.
Replace hoses every 5 years or 50,000 miles preventively.
- 2
Leaking radiator
Plastic radiator end tanks crack with age. Aluminum core seams corrode and leak. A small pinhole drip from the bottom of the radiator is often the first sign.
Old coolant (brown, rusty) corrodes aluminum radiators faster.
- 3
Failed water pump seal
The water pump weep hole is designed to leak coolant when the internal seal fails — alerting you before the bearing fails completely. A small drip directly below the water pump = seal failure.
Replace water pump at timing belt service interval to avoid emergency replacement.
- 4
Blown head gasket
A blown head gasket allows coolant to enter the combustion chamber (white exhaust smoke) or oil passages (milky oil). The most expensive cooling system failure.
Subaru EJ, GM Northstar V8, and Chevy 2.2L are known for head gasket issues.
How to Diagnose It
- 1
Place cardboard under the car overnight to confirm the leak and its location. Front-center under the engine = water pump or front hose. Front of car = radiator.
- 2
Clean the engine with degreaser, then run it to operating temp with the hood open. Use a flashlight to trace any fresh coolant weeping from hoses, clamps, or the radiator.
- 3
Check for head gasket failure: look for white, sweet-smelling smoke from the exhaust on a warm engine. Check the oil cap for milky residue. Use a combustion leak test kit ($15) to test for exhaust gases in the coolant.
How to Fix It
Leaking radiator hose
Drain the coolant, remove the old hose (loosen clamps), install the new hose and new clamps, and refill with fresh coolant. A 1–2 hour DIY job costing $15–$40 in parts.
Leaking radiator
Radiator replacement is intermediate DIY. Drain the system, remove the upper and lower hoses, disconnect the overflow tank and transmission cooler lines, unbolt the radiator, and install the new one. OEM-quality aluminum replacement radiators are $80–$150.
Blown head gasket
Shop recommendedThis requires removing the cylinder head. Advanced DIY only — most owners opt for a shop repair. Budget $1,500–$2,500.
Parts & Tools
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Mistakes to Avoid
- Don't use radiator stop-leak as anything more than a very temporary band-aid — it can clog the heater core.
- Don't mix coolant types — different colors are often different chemistries (OAT vs HOAT vs IAT).
- Don't drive with low coolant hoping the leak is slow enough — it often isn't.