Why you might find a puddle of water under your car on a hot day

On a hot day, your parked car may have a pool of water underneath its engine. What causes this, and should you be worried about it?

Air con

With Britain basking in hot weather, you may discover a puddle of water beneath your parked car – or indeed water dripping from the engine.

If so, you might assume the radiator has sprung a leak and the car is likely to overheat. However, it’s much more likely to be water dripping from the air conditioning system.

The excess water is caused by the air conditioning compressor working hard in hot conditions. Due to thermodynamics, the unit itself can freeze over as it takes moisture out of the car.

Check the water is clear and odourless

Car parked on a hot summer day

When the car is parked and the air conditioning is switched off, the ice on its surface will melt.

This is what causes the water underneath the car – and the hotter the weather, the larger and more alarming the puddle may be.

RAC spokesperson Rod Dennis revealed the car breakdown organisation receives plenty of calls from drivers worried by pools of water under their cars.

“The advice is to check whether this is simply odourless water, or if it has coolant in, with a definite smell and colour. If it’s the former, there should be no need to worry,” explained Dennis.

Hopefully, that’s panic over. Meaning it’s only the sunshine that will have you breaking a sweat during a heatwave.

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Motoring Research team
Motoring Research team
News, reviews, advice and features from the award-winning Motoring Resarch editorial team.

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