Water Pump To Thermostat Housing Gasket - 1900cc Waterboxer Engines

This replacement gasket seals the thermostat housing to the water pump on all 1900cc petrol Waterboxer engines fitted to VW Type 25 buses, from the start of production through to the end. It is a critical cooling system seal that prevents coolant leaks at the joint between the thermostat housing and the water pump.

On 1.9 Waterboxer engines, the thermostat housing bolts directly to the water pump. This gasket sits between the two mating faces and is responsible for maintaining a watertight seal under varying temperatures and pressures. Over time, heat cycling and coolant exposure can cause the original gasket to harden, compress, or split—often resulting in coolant seepage or more obvious leaks at the front of the engine.

Replacing this gasket is essential whenever:

• The thermostat is replaced

• The water pump is removed or renewed

• Coolant leaks are present around the thermostat housing

• A cooling system overhaul is being carried out

What this gasket does and how it works

The gasket compresses between the thermostat housing and the water pump as the bolts are tightened. This creates a sealed joint that allows coolant to circulate correctly through the thermostat and into the engine without external leaks. A sound gasket ensures stable operating temperatures, proper thermostat function, and long-term reliability of the cooling system.

Fitment

• Vehicle: VW Type 25

• Engine: 1900cc petrol Waterboxer

• Application: Thermostat housing to water pump gasket

• Production: Start of production to end of production

Engine code compatibility

• DF: 1.9 (08/82 – 07/92)

• DG: 1.9 (01/83 – 07/85)

• DH: 1.9 (01/83 – 07/85)

• EY: 1.9 (10/84 – 07/89)

• GW: 1.9 (08/83 – 07/85)

• SP: 1.9 (08/86 – 07/89)

Fitting notes / related parts

• Always clean both mating surfaces thoroughly before fitting

• Do not reuse old or crushed gaskets

• Lightly coating the gasket with coolant can help positioning during assembly

• Check the thermostat housing for corrosion or distortion before refitting

A small but vital sealing component, this gasket helps keep your 1.9 Waterboxer cooling system leak-free and operating at the correct temperature.