Type 25 Thermostat Housing (Lower Part) - 1983-85 - Waterboxer Engines

This replacement lower section of the thermostat housing is designed for early 1900cc petrol Waterboxer engines fitted to VW Type 25 / T3 buses produced from August 1982 to July 1985. It forms the base of the thermostat housing assembly, locating the thermostat itself and directing coolant flow within the early cooling system layout.

Manufactured from aluminium, this lower housing offers improved durability over original cast or ageing components, resisting corrosion, distortion, and repeated heat cycling. It is an essential part when rebuilding the thermostat housing, repairing coolant leaks, or restoring an early Waterboxer cooling system to proper working order.

What this part does and how it works

The thermostat sits inside the lower housing section. When the engine is cold, the thermostat remains closed, restricting coolant flow to allow the engine to warm up quickly. As operating temperature is reached, the thermostat opens and allows coolant to circulate through the radiator and engine.

The lower housing:

• Correctly locates the thermostat

• Forms the main coolant passage at the engine

• Provides a sealing surface for the upper thermostat housing components

Any corrosion, pitting, or distortion in this part can lead to coolant leaks or incorrect thermostat operation, making replacement critical if damage is present.

Fitment

• Vehicle: VW Type 25 / T3

• Years: 08/1982 – 07/1985

• Engine: 1900cc petrol Waterboxer

• Cooling system: Early type

• Application: Lower part of the thermostat housing

Correct for early Waterboxer cooling systems only
Not suitable for late (post-1985) thermostat housing designs

Construction

• Material: Aluminium

• Resistant to corrosion and heat cycling

• OE-style shape and coolant passages

Fitting notes

• Inspect the thermostat and replace if worn or unknown

• Always use new seals or O-rings where applicable

• Ensure all mating surfaces are clean and flat before assembly

• Tighten fasteners evenly to avoid distortion

• Refill with correct coolant and bleed the system thoroughly after installation

A vital early-model cooling component that ensures correct thermostat seating, reliable sealing, and stable engine temperatures on 1.9 Waterboxer Type 25 / T3 buses.