Parts for your 2006 Toyota Bb-Radiator cap

2006 Toyota bB radiator cap: is it used, and what does it do?

Yes, the 2006 Toyota bB is built with a radiator pressure cap, so a radiator-cap is relevant to this model. This is supported by technical sources including: Toyota Electronic Parts Catalog listings for the bB (QNC20/QNC21 series) that show a “Cap Sub-Assy, Radiator” on the upper tank of the radiator, Toyota bB workshop/repair manual procedures under Cooling System that include “Check radiator cap”, owner’s handbook cautions about never opening the radiator cap when hot, and Daihatsu Materia/Subaru Dex service references (sister vehicles to the bB) that specify a radiator pressure cap in the same cooling layout.

The radiator cap on a 2006 Toyota bB isn’t just a lid — it’s a pressure valve that keeps the cooling system at the right pressure so coolant can run hotter without boiling, helping the engine stay at a steady temperature even on a blazing Aussie or Kiwi summer day. It also works as a two-way valve: when things heat up, excess coolant is directed to the overflow bottle, when it cools down, the cap’s vacuum valve draws coolant back, keeping the system topped and free of air pockets.

As part of servicing a 2006 bB, the radiator cap deserves a quick once-over every time the bonnet’s up. A tired cap can cause hard-to-pinpoint dramas like gradual coolant loss, overheating in traffic, hoses collapsing as the engine cools, or an overflow bottle that keeps overfilling. If any of that’s going on, the cap’s spring or seals may be past it.

Good practice is to pressure-test the cap during routine cooling system checks and replace it every 3–5 years, or sooner if there’s cracking, swelling, corrosion, a sticky valve, or a weak spring. Always match the correct pressure rating stamped on the original cap for the QNC2# bB platform. Using a cap that’s too low can trigger boil-over, too high can stress hoses, the radiator core, or the heater matrix.

When fitting a new cap, make sure the engine is stone cold. Inspect the filler neck for nicks or corrosion, confirm the overflow hose is snug and not brittle, and top up with the correct Toyota Super Long Life Coolant (pink) or an approved equivalent premix. After refitting, run the engine to operating temp, check for leaks, verify the upper hose gets firm (pressure building properly), and confirm the overflow bottle level stabilises between marks. It’s a small, affordable part that pulls a lot of weight in keeping the bB happy on daily runs.

Popular questions

What pressure rating radiator cap does a 2006 Toyota bB use?

Most 2006 bB (QNC2# series) examples use a pressure cap in the common Toyota small-car range, often around 1.1 bar (approx. 108 kPa). Always check the number stamped on your current cap or verify against the Toyota parts catalog for your exact VIN. Matching the spec is important for reliable cooling and hose longevity.

How often should the radiator cap be replaced on a 2006 bB?

Have it inspected or pressure-tested at each service and plan to replace it every 3–5 years. Replace immediately if there are signs of perishing, corrosion, a weak spring, or if you’re chasing cooling issues like random overheating or coolant loss without visible leaks.

Where is the radiator cap on a 2006 Toyota bB?

On this model the pressure cap sits on the radiator’s top tank, just behind the grille area, slightly offset to one side. The translucent plastic bottle nearby is the overflow reservoir and is not the pressure cap location.