Coolant Leaking Under the Car — Where It Comes From

What's happening

Coolant leaves a sweet-smelling, brightly colored puddle. Position helps diagnose: under the front radiator → radiator or upper hose; middle of the engine → water pump or thermostat housing; passenger side rear → heater core feed lines (if your floor is wet, that is a heater core).

You might also notice

• Sweet-smelling puddle (do not let pets near it — coolant is toxic to animals)
• Coolant level dropping in the overflow tank
• Possible overheating
• White vapor from the engine bay when running

Likely causes (most common first)

1. Cracked radiator (often near a plastic end-tank seam)
2. Worn upper or lower radiator hose
3. Failed water pump (wet weep hole below the pump)
4. Cracked thermostat housing (especially on plastic housings — Ford, GM)
5. Failed intake manifold gasket (Chevy 4.3/5.7 Vortec, GM 3.4/3.8)
6. Heater core leak (interior smell + wet floorboards)
7. Cracked overflow reservoir

What to check first

1. With a clean cardboard under the parked car overnight, trace the leak source by location
2. Pressure-test the cooling system to find slow leaks (rent a tester at a parts store)
3. Check the heater core if your interior smells sweet or windows fog up with white film

Common OBD2 codes for this symptom

Don't have the code yet? Look up your code or read it with AXLY.pro.

Can I keep driving?

Slow leak: top off coolant, drive carefully, monitor temperature. Fast leak (visible drip while parked, or the gauge climbing): tow it.

Confirm with the actual code

Symptom-based diagnosis narrows the field — reading the actual stored code finishes the job. AXLY.pro is a free iPhone app that pairs with any Bluetooth OBD2 adapter and reads every stored DTC.