Parts for your 2017 Audi Q5-Radiator cap

2017 Audi Q5 radiator cap — what’s actually fitted

Chasing a radiator cap for a 2017 Audi Q5? Technically, that part isn’t used on this model. Audi’s 2017 Q5 (8R) runs a sealed cooling system with a remote, pressurised expansion tank, and the cap lives on that tank — not on the radiator itself. The cap performs the pressure and vacuum functions people usually associate with a “radiator cap”.

This setup is confirmed in Audi technical literature. The Q5 (8R) Owner’s Manual directs coolant checks and top-ups at the expansion tank only, while Volkswagen Group workshop documentation (ElsaPro/erWin cooling system procedures) shows system filling and bleeding via the expansion tank. The VW/Audi ETKA parts catalogue for Group 12 lists a coolant expansion tank cap (commonly referenced as 8K0 121 321 for many 8R models), and the radiator assembly is shown without a service cap or filler neck. Audi Self-Study Programme materials for EA888 engines also describe a closed cooling circuit with a de-gassing/expansion vessel and a pressure-rated cap.

Why doesn’t the Q5 have a traditional radiator cap? Modern Audi/VW radiators are slim, plastic–alloy units without a filler neck. Moving the pressure cap to the expansion tank improves access under the bonnet, makes bleeding air easier, and keeps hot, pressurised components away from the front of the car. The expansion tank cap maintains system pressure, bleeds excess pressure safely, and allows vacuum relief as the engine cools — exactly what a classic radiator cap used to do.

If someone’s hunting a “radiator cap” for this Q5, what they really want is the coolant expansion tank cap. Typical VAG caps are pressure-rated (often around 1.2–1.5 bar, model-dependent), and a tired cap can cause slow coolant loss or hard hoses. Replace the cap if its seal is cracked, the spring feels weak, or there’s staining around the tank neck. Only open the cap when the engine is stone cold, and top up with the correct Audi/VW-approved coolant (for 2017 models, G13 or as specified on the tank label), mixed to the right ratio with demineralised water. If in doubt, confirm the exact part number by VIN with an authorised Audi parts counter.

• No traditional radiator cap on the 2017 Q5 — it’s a pressurised expansion tank cap.
• Better access, safer pressure control, and easier bleeding are the reasons for the design.
• Replace the expansion tank cap if there are leaks, odours, or inconsistent cooling performance.

Popular questions about the 2017 Audi Q5 “radiator cap”

Where is the radiator cap on a 2017 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’s where you check levels and top up when the engine is cold.

Can the cap be replaced, and which part should be ordered?
Yes. Ask for a coolant expansion tank cap for a 2017 Audi Q5 (8R). A common reference is 8K0 121 321, but part numbers vary by engine and build, the safest bet is to confirm by VIN with an Audi parts department.

Is it safe to open the cap when the engine’s hot?
No. It’s a pressurised system. Opening the cap hot can release scalding coolant. Wait until the engine is completely cool, then open it slowly.