The Trust / GReddy 12400906 Radiator Filler Sealing Cap (Type‑N) is a non‑pressure, sealed radiator cap designed specifically for use with GReddy radiator breather tank systems. This cap contains no pressure relief valve and no vacuum valve.

When a breather tank is installed, coolant system pressure is managed at the breather tank rather than the radiator. In this configuration, the radiator filler neck must remain fully sealed, which is the purpose of the 12400906 filler sealing cap.

Key Features

• GReddy Type‑N radiator filler sealing cap
• No pressure or vacuum relief valves
• Completely seals the radiator filler neck
• Designed for GReddy breather tank installations
• Prevents incorrect pressure release at the radiator
• Made in Japan by TRUST

Type‑N Compatibility

The 12400906 is a Type‑N filler sealing cap, intended for vehicles that use a Type‑N radiator neck. According to GReddy’s application guide, Type‑N filler caps are commonly associated with Honda and Toyota platforms, as well as other vehicles that utilise Type‑N radiator necks when fitted with breather tank systems.

This cap is not vehicle‑specific. Correct fitment depends on radiator neck type and cooling system configuration, not vehicle model alone.

Why & When Is a Radiator Filler Sealing Cap Used?

A radiator filler sealing cap is required when the cooling system has been modified to use a remote pressure cap, such as a GReddy radiator breather tank. In this setup:

• The pressure radiator cap is installed on the breather tank
• The radiator filler neck must be sealed
• Cooling system pressure is controlled from one location only

Using a standard pressure radiator cap on the radiator in this configuration can lead to incorrect pressure regulation, coolant loss, or air entering the system. The 12400906 sealing cap eliminates these issues by keeping the radiator completely sealed.

Important:

• This cap must not be used as a pressure radiator cap
• Only install when a separate pressure cap is fitted to a breather tank
• Cooling system components must be in good condition before use