The Trust / GReddy 12400907 Radiator Filler Sealing Cap (Type‑S) is a non‑pressure, sealed radiator cap designed for use with GReddy radiator breather tanks. Unlike a standard radiator cap, this filler cap contains no pressure relief or vacuum valve.

This cap is installed on the radiator filler neck when a breather tank (or remote pressure cap setup) is used. In these systems, coolant system pressure is controlled only by the radiator cap mounted on the breather tank, not at the radiator itself.

Key Features

• GReddy Type‑S radiator filler sealing cap
• No pressure or vacuum relief valves
• Seals the radiator filler neck completely
• Designed for use with GReddy breather tanks
• Prevents incorrect pressure release at the radiator
• Made in Japan by TRUST

Type‑S Compatibility

The 12400907 is a Type‑S filler sealing cap, intended for vehicles that use a Type‑S radiator neck. In GReddy’s application guide, Type‑S filler caps are typically associated with Nissan, Mazda, Subaru, and related platforms when fitted with GReddy breather tank systems.

This cap is not vehicle‑specific; fitment depends on radiator neck type and breather tank configuration.

Why & When Is a Radiator Filler Sealing Cap Used?

A radiator filler sealing cap is used when the cooling system has been modified to relocate the pressure cap from the radiator to a remote breather tank. In this configuration:

• The pressure radiator cap is installed on the breather tank
• The radiator filler neck must remain sealed
• System pressure is controlled at one point only

Using a standard radiator cap on the radiator in this setup can cause incorrect pressure regulation, coolant loss, or air ingestion. The 12400907 sealing cap prevents this by ensuring the radiator remains fully sealed with no pressure release.

Important:

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