Išsiplėtimų bakelio pirkimo vadovas
Paskutinį kartą atnaujinta: 2026 m. balandžio 24 d.
The coolant expansion tank (header tank) maintains correct coolant volume as the system heats and cools. It allows coolant to expand safely under pressure and provides a fill point for topping up. Cracked or leaking tanks are a common cause of coolant loss and overheating. At CarParts247 we stock expansion tanks from Febi Bilstein, Behr, and Valeo.
Expansion tank failure signs
Plastic expansion tanks become brittle with age and heat exposure. Hairline cracks may only leak when the system is hot and pressurised, making them hard to spot.
- Coolant level dropping with no visible external leak — hairline crack leaks only when hot
- White residue or coolant stains around the tank or cap
- Sweet coolant smell from the engine bay
- Overheating due to low coolant level
- Visibly cracked, discoloured, or bulging tank
Replacement and system care
Expansion tank replacement is usually straightforward. Take the opportunity to inspect hoses, the pressure cap, and coolant condition at the same time.
- Replace the pressure cap when fitting a new tank — a weak cap causes premature failure
- Flush and fill with the correct coolant specification — do not mix types
- Bleed the cooling system to remove air pockets after refilling
- Check the coolant level sensor connector if your vehicle has a low-coolant warning
- Inspect all coolant hoses for swelling, softness, or cracking while the system is drained
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Dažnai užduodami klausimai
Why does my coolant keep disappearing?
The most common cause of invisible coolant loss is a hairline crack in the expansion tank that only leaks under pressure when hot. The coolant evaporates on the hot engine, leaving little trace.
Can I use any coolant to top up?
No. Mixing incompatible coolant types (e.g., silicate with OAT) causes gelling and corrosion. Use the manufacturer-specified type, or flush and refill with a universal long-life coolant.
How often should the expansion tank be replaced?
There is no fixed interval, but tanks on vehicles over 8-10 years old should be inspected for discolouration and brittleness. If in doubt, replace preventively — they are inexpensive.
Is the expansion tank cap important?
Yes. The cap is a calibrated pressure relief valve. A weak cap lowers the system pressure, reducing the boiling point and causing premature failure of hoses and the tank.
Susiję gidai
No cold air, clutch not engaging, and seized compressors — A/C compressor types, oil charging requirements, and new vs remanufactured options.
Coolant Flange Buying GuideCoolant flanges, thermostat housings, and outlet pipes — plastic vs aluminium, common failure modes, and correct sealant for leak-free installation.
Coolant Temperature Sensor Buying GuideIncorrect temperature gauge, poor fuel economy, and cooling fan issues — diagnosing a faulty coolant temperature sensor and selecting a replacement.
Engine Oil Cooler Buying GuideWater-cooled vs air-cooled oil coolers, oil-in-coolant mixing symptoms, and how to choose and fit a replacement oil cooler without disturbing the coolant system.
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