Sweet Smell / Coolant Leak

What's happening

Most likely causes

1. 1

   Leaking radiator hose

   Cracked or soft hoses weep at the clamps.

2. 2

   Failing water pump

   Weeps from the weep hole before failing outright.

3. 3

   Leaking heater core

   Sweet smell inside the cabin with foggy windows; the worst one to replace.

4. 4

   Cracked overflow tank

   Plastic tanks crack with age and leak only when hot.

5. 5

   Head gasket leak

   Coolant disappearing with no puddle and white exhaust smoke is the warning sign.

How to diagnose it — in order

1. 1

   Check the coolant reservoir level when cold; top up and monitor how fast it drops.

2. 2

   Look for colored residue around hose clamps, the water pump, and radiator seams.

3. 3

   Sweet smell inside the cabin points at the heater core.

4. 4

   Pressure-test the system to find seeps that only leak when hot.

Trouble codes tied to this symptom

If your scanner shows one of these, read its dedicated trouble-code page for the full diagnosis.