Car losing coolant: where is it going?

What a dropping coolant level means

A level that drops over time means the coolant is escaping. It is either leaving the system through the radiator, a hose or the water pump, or, in the more serious case, going into the engine itself.

How the cooling system protects the engine

Coolant circulates through the engine and radiator, carrying heat away. The system is sealed and pressurized on purpose, because pressure raises the coolant's boiling point and lets the engine run hotter without it boiling.

Common causes

• A radiator leak, from corrosion or damage from road debris
• A cracked, bulging or soft hose
• A failing water pump seal, often showing at its weep hole
• Coolant entering the combustion chamber, seen as persistent white exhaust smoke

What to do now

1. Let the engine cool fully, ideally at least 30 minutes, before you open or check anything.
2. Check the level in the reservoir against the min and max markings.
3. Look for a colored puddle under the front of the car, and note its color and location.
4. With the engine cold, check the visible hoses for cracking, bulging or soft spots.
5. Notice whether there is a sweet smell after driving, or the heater is blowing cool air.
6. Top up only with the coolant type in your owner's manual, and have the leak found.

Leaking out, or going into the engine?

• Colored puddle under the front, sweet smell: an outside leak from the radiator, a hose or the water pump.
• Leak near the pump, with a whining or grinding noise: a failing water pump.
• White exhaust smoke that persists after warmup: coolant entering the combustion chamber, get it checked urgently.
• Heater blowing cool air: low coolant, or a thermostat stuck open.
• Steam from under the hood: pull over, shut the engine off, and do not open the hood.

What people often get wrong

That topping up with plain water is fine. Water alone lacks the corrosion protection and the higher boiling point and lower freezing point of proper coolant. Different coolant types are not always compatible either, so check the manual before you mix.

When the car must go to a workshop

White smoke together with overheating deserves a same-day look. If the gauge climbs into the red, follow the overheating steps and have the system inspected. Refilling and bleeding the system is a job for a professional, because trapped air can cause serious engine damage.

Read next

• P0128: the thermostat is stuck open
• Car burning oil: how to tell and what it means
• Oil pressure warning light: stop the car now

This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.