Parts for your 2016 Toyota Bb-Radiator cap

2016 Toyota bB radiator-cap: what it does and when to replace it

Based on Toyota’s technical literature and catalogues, the 2016 Toyota bB does use a conventional pressurised radiator cap. The Toyota bB QNC2# series cooling-system section in the workshop manual includes “Radiator Cap” inspection/testing, and Toyota’s electronic parts catalogue lists a serviceable “radiator cap sub-assy” for these models. Major aftermarket catalogues also specify a cap for the 2005–2016 bB at around 0.9 bar (approx. 88–108 kPa), confirming the part is fitted and relevant.

On the 2016 Toyota bB, the radiator cap is a small but critical bit of kit. It seals the system and holds pressure so coolant can run hotter without boiling, keeping the engine stable on steep climbs, summer days, and motorway slogs. Inside the cap is a spring-loaded pressure valve that releases excess pressure to the overflow bottle when things get hot, and a vacuum valve that draws coolant back in as the engine cools. That two-way action helps prevent air pockets, hose collapse, and random coolant loss.

As part of routine servicing, the cap deserves a proper look. A weak spring, nicked rubber seal, or corroded seat can drop system pressure and spark symptoms like gradual overheating, hard upper hoses, or a low overflow bottle despite no obvious leaks. Technicians typically pressure-test the cap and the system, if the cap can’t hold the specified rating, it’s time for a new one.

When replacing, match the pressure rating specified for the bB (commonly ~0.9 bar). Swapping to the wrong rating can invite overheating or stress other cooling components. Only remove the cap when the engine is stone cold—under the bonnet pressure burns aren’t worth the risk. While there, they’ll also check the overflow hose for cracks and ensure the bB is running the right coolant (Toyota Super Long Life Coolant, pink) mixed correctly.

• Inspect the cap at every service, replace at the first sign of seal damage, rust, or failing a pressure test.
• Watch for tell-tales of a dud cap: rising temps under load, coolant smell after drives, collapsed upper hose when cold, or the overflow not returning coolant.
• After cap replacement, bleed the cooling system per the workshop procedure to keep air out.

Popular questions

What pressure radiator cap does the 2016 Toyota bB use?
Most catalogues list a cap around 0.9 bar (about 88–108 kPa) for the QNC2# bB. The exact rating is printed on the cap itself and is also specified in Toyota’s service information. Matching that rating is important for proper boiling-point control and system balance.

How often should the radiator cap be replaced on a 2016 bB?
There’s no hard interval in many schedules, but the cap should be inspected at each service and pressure-tested when diagnosing cooling issues. In practice, many workshops will replace the cap proactively around major cooling-service intervals or at the first sign of seal wear, corrosion, or a failed test.

Where is the radiator cap on the bB?
It’s typically on the radiator neck near the top of the radiator under the bonnet. Some variants route the cap to a pressurised reservoir, either way, it will be the metal cap marked with a pressure rating and warning labels.