What causes sudden coolant loss and engine overheating in the Kia Stonic even when there are no visible leaks?

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What causes sudden coolant loss and engine overheating in the Kia Stonic even when there are no visible leaks?

I’ve noticed that my Kia Stonic loses coolant over time and sometimes overheats, but there’s no visible leak under the car o r in the engine bay. Could this be due to a radiator cap issue, internal leak like a head gasket, o r slow evaporation under high engine temps in Pakistan? Has this been a common issue for Stonic owners here, and how can I properly diagnose it?

Talha Kyanii asked on 20 Sep 2025 16:48:15 pm

1 Answer

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Gari Master - on 20 Sep 2025 16:58:10 pm

Likely Causes in Pakistan:

Radiator fan not engaging properly — In traffic, your car relies on the radiator fan to cool the engine. If the fan motor, relay, o r temperature sensor is faulty o r weak, heat builds up fast when the AC is running.

Overworked AC system — The condenser in front of the radiator gets hot with AC use, which adds heat load to the radiator. If airflow is low no movement + dirty fins, overheating can happen.

Clogged radiator fins — Dust, bugs, and smog particles in Pakistani cities reduce airflow efficiency through the radiator and condenser.

Old o r diluted coolant — If youre using tap water o r expired coolant, the boiling point s, and cooling efficiency suffers.

What Most Owners Do:

Clean the radiator and AC condenser fins with pressure air o r water.

Check that the radiator fan turns on automatically when engine heats up o r AC is on.

Replace coolant with a high-boiling-point, pre-mixed coolant — not tap water o r home-mixed.

Inspect o r replace the thermostat if it opens too late.