Knowledge base · Symptom & cause
Coolant disappearing with no visible leak — where does it go?
You top up coolant every few weeks, yet there is never anything under the car. It is still going somewhere — coolant does not simply evaporate out of a sealed system. These are the four places we look first.
1. A small leak that evaporates before it drips
The cooling system is pressurised and gets hot. A hairline crack in a hose, a weeping connection or a porous radiator lets fluid escape that evaporates straight onto hot components. You see no puddle, but you do see white or coloured residue around a hose clamp or on the radiator. Often there is a sweetish smell after driving.
2. The head gasket
The most serious version: coolant leaks internally into the combustion chambers and disappears through the exhaust. Signs: white smoke that doesn't clear on a warm engine, mayonnaise-like residue under the oil cap, bubbles in the expansion tank, a rising temperature gauge or a car that "gurgles" after switching off. Driving on here is genuinely unwise — an overheated engine means warped cylinder heads.
3. The heater matrix
If the leak is in the heater matrix, the fluid ends up inside the car rather than on the road. Recognisable by: a sweetish smell in the cabin, a greasy film on the inside of the windscreen that keeps returning, or a wet passenger footwell. Seeing that together with misted windows? Read damp in the car too.
4. The cap and the expansion tank
The filler cap holds the system at pressure. If it no longer seals properly, a little vapour escapes on every warm run — just enough to cause a noticeable shortfall after a few weeks. The cheapest part on this list, and therefore the first thing we check. A hairline crack in the expansion tank itself is also common.
What you can do yourself
- Always check the level on a cold engine — when warm the system is pressurised and the cap can spray fluid out.
- Look around hose clamps, the water pump and the radiator for white or coloured stains.
- Smell under the bonnet: coolant has a characteristic sweet odour.
- Watch the temperature gauge; a red temperature light means stop immediately.
- Top up with the correct type of coolant. Mixing types can cause gelling — just ask us if you are unsure.
How we find the leak
We pressure-test the cooling system: the system is put under pressure with the engine off, after which a leak reveals itself without everything being hot and wet. If a head gasket is suspected we also test whether combustion gases are present in the coolant. That way we know whether it is a ten-euro hose or engine work — before anything is dismantled.
The repair itself happens in our own workshop — engine repair in Tilburg.