Parts for your 2015 Audi Q5-Radiator cap

2015 Audi Q5 radiator-cap: is there one, and what should owners know?

Short answer: a traditional “radiator cap” isn’t used on the 2015 Audi Q5 (8R). Audi’s cooling system on this model seals and regulates pressure via the coolant expansion tank (also called the header tank) cap, not a cap mounted directly on the radiator.

This isn’t guesswork. Audi’s 2015 Q5 Owner’s Manual (Cooling system section) shows the pressure cap only on the expansion tank. Audi’s factory repair information (ELSA/erWin: Cooling System – Draining/Filling/Pressure test procedures) instructs technicians to open and test at the expansion tank cap. The parts catalogue (ETKA for 8R Q5) lists a cap for the expansion tank (commonly referenced under the cooling reservoir), while the radiator assembly itself has no service cap. Audi Self‑Study Program material for the applicable engines (e.g., 2.0 TFSI, 3.0 TDI) also describes a sealed, pressurised system with a remote expansion tank handling fill, venting and pressure control.

Why there’s no radiator cap on this Q5:

• Sealed, remote expansion system: The expansion tank sits high in the bay under the bonnet, becoming the single fill and pressure point. That keeps the radiator a closed unit for reliability.
• Better packaging and cooling efficiency: With modern crossflow aluminium radiators tucked behind crash structures, a separate cap isn’t practical.
• Simpler service and bleeding: Air purges through the top tank, techs work from one cap for filling, testing and venting.

What owners should do instead of looking for a radiator cap:

• Inspect the coolant expansion tank cap for cracked seals, sticky valves or coolant staining. A tired cap can cause slow coolant loss, hard hoses, or running hotter than normal.
• Replace the cap with an OE‑spec part if there’s any doubt, especially if chasing cooling faults. It’s inexpensive and often overlooked.
• Only open the cap when the engine is stone cold. Use the specified Audi coolant and top up to the correct mark.
• If frequent top‑ups are needed, have the system pressure‑tested at the expansion cap to check for leaks or a weak cap spring/valve.

So if a workshop or parts listing mentions a “radiator cap” for a 2015 Q5, they’re really talking about the coolant expansion tank cap. That’s the bit to check, test and replace during routine servicing.

FAQs

Where is the radiator cap on a 2015 Audi Q5?
There isn’t one on the radiator. The only service cap is on the coolant expansion (header) tank, mounted high in the engine bay. That’s where you fill, test system pressure and vent air.

What should be replaced if told the radiator cap is faulty on a 2015 Q5?
Ask for a new coolant expansion tank cap to the correct Audi pressure spec. A weak or leaking cap can cause overflow, low coolant warnings, or higher running temperatures.

How does one safely top up coolant on a 2015 Q5?
Let the engine cool completely, open the expansion tank cap slowly, top up with the specified Audi coolant mix to the mark, refit the cap firmly and check for leaks. If levels keep dropping, book a pressure test at the cap.