The coolant reservoir in a 2015 Audi A3 is the expansion tank located in the engine bay on the passenger side. When the engine is cold, open the reservoir cap and fill it with a VW/Audi-approved coolant (typically G13 or a compatible long-life mix) up to the MAX line, then replace the cap and check for leaks after the engine warms up.
Where to locate the coolant reservoir
In the 2015 A3, the expansion tank sits in the engine bay toward the passenger side, near the firewall and radiator. It is a translucent plastic tank with MIN and MAX level marks, and it typically has a black or blue cap labeled for coolant. The tank connects to the cooling system with hoses that run to the radiator and the engine.
What coolant should I use?
Using the correct coolant is essential to protect the cooling system and avoid damage. For most 2015 Audi A3 models, use a VW/Audi approved long-life coolant, commonly G13 (pink) or a compatible G12/G12+ formulation. These are usually premixed 50/50 with distilled water, but always follow the product instructions and the vehicle’s manual. Do not mix different coolant types unless the manufacturer explicitly allows it.
Coolant types and compatibility
G13 is the preferred VW/Audi specification in many markets. It is compatible with other VW/Audi approved long-life coolants (such as G12/G12+ in some regions), but avoid mixing coolant types that aren’t confirmed compatible. If you’re unsure, use a premixed 50/50 VW/Audi approved coolant and confirm the product label matches the vehicle’s requirements listed in the owner’s manual.
How to check and fill coolant
Follow these steps to check the level and add coolant safely. The list is designed to keep you from opening the system when it’s under pressure and to ensure the correct fill level.
- Park on level ground and allow the engine to cool completely before touching the reservoir.
- Open the hood and locate the expansion tank on the passenger side of the engine bay.
- Check the level against the MIN and MAX marks on the translucent reservoir chamber.
- If the level is between MIN and MAX, you generally do not need to add coolant yet; if below MIN, proceed to fill.
- Slowly loosen the reservoir cap while wearing eye protection and keep your face away from the opening; wait if there is any pressure release (only when cool).
- Pour in a 50/50 mix of VW/Audi approved coolant and distilled water up to the MAX line, avoiding overfill.
- Replace the cap securely and run the engine with the heater set to hot to circulate coolant; after the engine reaches operating temperature, recheck the level when the engine is cool and top up if necessary.
- Look for leaks around the reservoir, hoses, and radiator connections; address any leaks promptly.
Resting the system and verifying levels after a brief drive can help identify any small air pockets or leaks that need attention.
Safety and maintenance tips
Keep these safety tips in mind to protect yourself and the cooling system integrity.
- Never open the coolant reservoir cap while the engine is hot or under pressure.
- Only use VW/Audi approved coolant (G13 or a compatible long-life formulation) and follow the 50/50 premix unless otherwise directed by the product label.
- Avoid mixing different coolant brands or types unless compatibility is explicitly stated by VW/Audi.
- Dispose of old or unused coolant at a proper recycling facility; it is toxic and should not be poured down drains.
- If you notice persistent low levels, overheating, or visible leaks, have the cooling system inspected by a qualified mechanic.
Note: If the expansion tank cap is damaged, or if you observe cracks in the reservoir, have the component replaced rather than attempting to repair it.
Summary
To add coolant on a 2015 Audi A3, locate the expansion tank on the passenger side of the engine bay, ensure the engine is cold, and fill the reservoir to the MAX line with a VW/Audi approved coolant (G13 or compatible) using a 50/50 mix with distilled water if required. Re-cap securely, run the engine to circulate, recheck the level once cool, and monitor for leaks or changes in level. Always follow the owner’s manual and safety precautions when performing any work on the cooling system.