Parts for your 2018 Audi Q5-Radiator cap

2018 Audi Q5 radiator cap — is there one?

Short answer: a traditional radiator cap isn’t used on the 2018 Audi Q5. Audi routes cooling-system pressure control through a sealed, pressurised coolant expansion tank (also called a degas bottle), not a cap on the radiator itself. This setup is documented in Audi’s technical sources, including the 2018 Q5 Owner’s Manual (cooling system section), the Audi ElsaPro/Workshop Manual for the FY-series cooling system, and the Volkswagen Group ETKA parts catalogue, all of which show a pressurised reservoir cap and a sealed radiator with no filler neck.

Why the change from the old-school radiator cap? Modern Audi cooling systems use a remote, pressurised expansion tank to do several jobs at once: it raises the boiling point by holding system pressure, continuously separates air from coolant, and gives a single, safe fill point away from the hot radiator core. It also improves front-end packaging and crash safety by removing a service cap from the radiator. Bleeding and top-ups are done at the tank, while the radiator stays sealed.

What should be serviced instead of a radiator cap? The coolant expansion tank cap is the hero here. It contains the pressure valve that keeps the system at the specified pressure (check the kPa/bar rating moulded on the cap). If the cap can’t hold pressure, coolant can boil earlier, hoses can collapse as the engine cools, and small leaks may appear around hose joints.

• Check the cap and tank regularly for crusty pink residue, cracks, perished O-rings, or coolant odour under the bonnet after a drive.
• If there’s unexplained coolant loss, have the cooling system and cap pressure-tested to the value printed on the cap (workshop tools do this quickly).
• Only open the cap when the engine is stone-cold. Crack it slowly to release any residual pressure.
• Use Audi-approved coolant (G12evo/G13 family) mixed with demineralised water to the correct ratio (often 50/50). Don’t mix in generic green or silicated coolants.
• After cap replacement or a top-up, fill to the MAX mark, run the engine with the heater on HOT to purge air, let it cool, then recheck the level.

There’s no fixed replacement interval for the expansion tank cap, but given Australia and New Zealand’s heat and big kilometre use, swapping a tired cap every few years—or at the first sign of pressure loss—is inexpensive insurance for the Q5’s alloy engine and turbo hardware.

FAQs

Where is the “radiator cap” on a 2018 Audi Q5?
There isn’t a cap on the radiator. The pressurised cap is on the coolant expansion tank (degas bottle) in the engine bay. That’s the only place you should open for coolant checks or top-ups—always when the engine is cold.

What pressure is the Audi Q5 expansion tank cap rated to?
Most factory caps for this model sit around 1.2–1.5 bar (120–150 kPa), but always go by what’s stamped on the cap. If the system won’t hold that pressure during a test, replace the cap and recheck for leaks.

Which coolant should be used in a 2018 Audi Q5?
Use Audi-approved G12evo/G13-spec coolant. It’s typically pink/violet and designed for alloy engines and long service life. Top up with the correct premix or with demineralised water and concentrate to the right ratio. Avoid mixing with non-approved “universal” coolants.