Parts for your 2013 Audi Q5-Radiator cap

2013 Audi Q5 radiator cap — what’s actually fitted

There’s no traditional radiator-mounted cap on a 2013 Audi Q5 (8R). Instead, Audi uses a sealed, pressurised cooling system with a remote coolant expansion (surge) tank. The pressure cap lives on that tank and does the job a classic “radiator cap” used to do. This layout is confirmed by Audi’s workshop information (erWin service manuals describe a sealed, pressurised system with an expansion tank cap as the pressure relief valve), the Audi Owner’s Manual warning to only open the coolant expansion tank cap when the engine is cool, and the Audi parts catalogue (ETKA) for the 8R Q5 listing an expansion tank cap (commonly referenced as VAG 8K0 121 321) while the radiator itself has no cap.

Why no radiator cap? Modern Audi cooling packages place the radiator low in a tightly packaged front-end module, with a separate, high-mounted expansion tank that’s the system’s fill and bleed point. That tank’s cap controls pressure and venting, improves self-bleeding of air, and simplifies servicing. It also reduces leak points on the radiator, keeps hot pressurised openings away from the crash zone, and helps with consistent coolant levels across different engine variants.

If someone is chasing a “radiator cap” for a 2013 Q5, what they actually need is the coolant expansion tank cap. It’s the blue or black cap on the translucent reservoir in the engine bay. Use a genuine or high-quality OE-equivalent cap with the correct pressure rating (typically about 1.2–1.5 bar, check the printing on the cap and the vehicle’s build data). Open only when the engine is completely cool. If the cap’s seal is cracked, the vent sticks, or there’s a whiff of coolant after parking, it’s smart to replace it. When servicing, top up with the correct Audi/VW-approved coolant (e.g., G12++/G13) mixed with demineralised water to the right ratio, and inspect the reservoir neck for damage before fitting the new cap.

• Common signs a cap’s on the way out: unexplained coolant loss, dried pink residue near the tank, collapsed radiator hoses after cooldown, overheating under load, or frequent low-level warnings.

1. Let the engine cool fully.
2. Remove the old cap, check the O-ring and vent for cracks or grit.
3. Wipe the tank neck clean, fit the new cap hand-tight until it seats.
4. Top up to the “MAX” mark, run the engine to temperature with the heater on, and recheck the level.

Technical sources referenced: Audi erWin Workshop Information for 8R Q5 (sealed cooling system with expansion tank), Audi Q5 Owner’s Manual (coolant expansion tank cap handling), Audi ETKA parts catalogue for 8R Q5 (expansion tank cap listed, no radiator-mounted cap).

FAQs

Where is the radiator cap on a 2013 Audi Q5?

There isn’t a cap on the radiator. The pressure cap is on the coolant expansion tank — the translucent reservoir in the engine bay. That cap is the fill point and pressure control for the system.

What cap part should be used on a 2013 Q5?

Use a genuine or OE-quality expansion tank cap with the correct pressure rating (around 1.2–1.5 bar). For many 8R Q5 models the commonly cited VAG part is 8K0 121 321, but always verify by VIN.

How can someone tell if the cap is failing?

Look for coolant smells after driving, dried pink residue around the tank, hoses that collapse when cold, rising temps in traffic, or recurring low-coolant warnings. Any of these are a cue to test or replace the cap.