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

This replacement thermostat housing is designed for the early cooling system fitted to VW Type 25 / T3 watercooled petrol models from August 1982 to July 1985. It is suitable for all early 1.9 Waterboxer engine codes, making it an essential component when repairing, rebuilding, or restoring early T3 cooling systems.

On early Waterboxer engines, the thermostat housing forms the central junction for coolant flow and sensor locations. It houses the thermostat and provides threaded ports for temperature sensors used by the engine management and cooling system. Because of age and repeated heat cycles, original housings often suffer from corrosion, pitting, cracked threads, or warped sealing faces, all of which can lead to coolant leaks or inaccurate temperature readings.

This replacement restores correct coolant routing and thermostat positioning, ensuring reliable warm-up and stable operating temperatures.

What this part does and how it works

The thermostat sits inside this housing and controls coolant flow based on engine temperature.

• When the engine is cold, the thermostat remains closed to speed up warm-up

• As operating temperature is reached, it opens and allows coolant to circulate through the radiator

The housing also provides mounting points for coolant temperature sensors used by the cooling system and dashboard gauge.

For DG and DF engines, one of the threaded sensor ports is not used and must be blanked off to suit the vehicle’s original configuration.

Fitment

• Vehicle: VW Type 25 / T3

• Model years: 08/1982 – 07/1985

• Fuel type: Watercooled petrol

• Cooling system: Early type

Engine code compatibility

• DW – direct fit

• DG – requires one threaded sensor port to be blanked

• DF – requires one threaded sensor port to be blanked

Correct for early Waterboxer cooling layouts only
Not suitable for late (post-1985) cooling systems

Fitting notes

• Always inspect the thermostat and replace if in doubt

• Use new seals/O-rings where applicable

• Blank unused sensor ports correctly on DG and DF engines

• Tighten fittings evenly to avoid cracking or distortion

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

A vital cooling system component that ensures correct thermostat operation, leak-free sealing, and stable engine temperatures on early watercooled T3 petrol models.