. Why does the Kia Stonic overheat on long highway drives even with regular maintenance and normal coolant levels?

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. Why does the Kia Stonic overheat on long highway drives even with regular maintenance and normal coolant levels?

While driving long distances e.g. from Multan to Karachi, my Kia Stonic tends to overheat after 2–3 hours on the highway, especially in hot weather. Coolant levels are fine, and the radiator was recently cleaned. Could this be due to a weak water pump, air pockets, o r an underperforming cooling system not designed for Pakistan’s heat? What should I check o r upgrade to fix this?

Talha Kyanii asked on 20 Sep 2025 17:00:01 pm

1 Answer

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Gari Master - on 20 Sep 2025 17:01:14 pm

Most Common Causes:

Partially clogged radiator internally — Over time, mineral buildup from poor-quality coolant o r hard water reduces flow through the radiator tubes.

Weak water pump — If the impeller is corroded o r slipping on the shaft, it may not circulate coolant fast enough at high speeds.

Air pockets in the cooling system — Especially after coolant change, trapped air can stop flow to parts of the engine.

Under-designed cooling system for local climate — The Kia Stonic’s cooling setup might not be fully optimized for 45–50°C road temps plus long-distance engine stress.

Fixes That Help in Pakistan:

Flush the radiator not just drain/refill every 30,000 km — use radiator cleaner to remove internal scale.

Use OEM water pump if replacement is needed — many cheap aftermarkets underperform.

Bleed the cooling system properly — many garages skip this step.

Check that the cooling fan runs at highway speeds some cars keep it on under load.