BDFHYK Engine Coolant Expansion Reservoir Overflow Tank Replacement
This BDFHYK engine coolant expansion reservoir overflow tank is designed as an OE-style replacement for selected Audi allroad, Q5, A4, and A5 Quattro applications. It helps replace an aging, cracked, stained, or leaking coolant reservoir while keeping fitment and OE-number confirmation clear before purchase.
Fitment Reference
Compatible with selected Audi allroad, Q5, A4, and A5 Quattro applications from the listed product range. Please confirm your exact year, model, engine, mounting points, hose layout, and original part number before ordering.
OE / Interchange Reference
- 8K0121403Q
- V10-4478
- 8K0121403T
- 8K0121403D
Reference numbers are provided for fitment comparison only. Match your original reservoir or vehicle parts catalog before installation.
Common Replacement Signs
- Cracked, yellowed, or brittle reservoir plastic
- Coolant seepage around the tank body or hose connections
- Repeated low coolant level after topping off
- Sweet coolant smell after driving
- Coolant puddles under the vehicle
- Hard-to-read coolant level marks
Before You Buy
- Compare your original reservoir with the product images.
- Check hose connections and mounting points.
- Verify the OE or interchange number when available.
- Confirm whether your setup requires a specific cap, sensor, or hose arrangement.
Installation Notes
- Install only when the engine is fully cool.
- Do not open a hot or pressurized cooling system.
- Inspect hoses, clamps, radiator cap, thermostat area, and nearby connections during replacement.
- Refill and bleed coolant according to the vehicle service procedure.
- Professional installation is recommended if you are not familiar with cooling system service.
About BDFHYK
BDFHYK focuses on OE-style replacement parts that help drivers move from vehicle symptoms to the right replacement part with less guesswork.
