Type 25 Thermostat Housing Flange Gasket - 1983-85 - Waterboxer Engines

This replacement thermostat housing gasket fits early Waterboxer cooling systems on VW Type 25 / T3 buses equipped with 1900cc petrol Waterboxer engines. The gasket is located between the thermostat housing and the cylinder head, providing a critical seal to prevent coolant leaks at one of the hottest and most highly stressed joints in the cooling system.

On pre-1985 Waterboxer engines, the thermostat housing can be identified by the fact that it is bolted directly to the water pump. This gasket is specific to that early design and is not interchangeable with later cooling system layouts.

Over time, the original gasket can compress, harden, or degrade due to heat cycles and coolant exposure, leading to coolant seepage, pressure loss, and air ingress. Replacing this gasket during cooling system service or thermostat housing removal is essential for reliable operation.

What this gasket does and how it works

The gasket forms a watertight seal between the thermostat housing and the cylinder head. As coolant flows through the housing and thermostat, the gasket prevents leaks and ensures the system can maintain correct pressure. A sound seal here is vital for:

• Stable coolant circulation

• Proper thermostat operation

• Preventing coolant loss and air locks

Fitment

• Vehicle: VW Type 25 / T3

• Years: 08/1982 – 07/1984

• Engine: 1900cc petrol Waterboxer

• Engine code: DG

• Cooling system: Early type (thermostat housing bolted directly to water pump)

• Application: Thermostat housing to cylinder head gasket

Early Waterboxer engines only
Not suitable for late (post-1985) cooling systems

Construction

• Designed to original thickness and profile

• Resistant to coolant, heat, and compression set

• Direct replacement with no modification required

Fitting notes

• Thoroughly clean both mating surfaces before installation

• Check the thermostat housing and cylinder head for corrosion or pitting

• Tighten fasteners evenly to avoid distortion

• Always refill with the correct coolant and bleed the system fully after fitting

A small but essential sealing component that helps keep your early 1.9 Waterboxer Type 25 cooling system leak-free, properly pressurised, and running at the correct temperature.