Type 25 Syncro Thermostat Housing - 1986-92 - Waterboxer Engines

This aluminium thermostat housing is a high-quality replacement designed exclusively for Syncro models fitted with 1900cc and 2100cc petrol Waterboxer engines from 1985 onwards. It fits VW Type 25 / T3 Syncro vans and is not suitable for non-Syncro (2WD) models.

Unlike earlier plastic housings, this version is manufactured from cast aluminium, offering greatly improved durability and resistance to heat cycling, cracking, and warping. It is ideal for long-term reliability, off-road use, and restorations where strength and longevity are priorities.

Important design note:
This housing uses screw-in temperature switches/senders, not the clip-in style found on some other Waterboxer thermostat housings.

What this part does and how it works

The thermostat housing secures the thermostat and directs coolant flow within the engine. When the engine is cold, the thermostat remains closed to allow rapid warm-up. As operating temperature is reached, it opens and allows coolant to circulate through the radiator and cooling system.

A solid, accurately machined housing is essential to:

• Keep the thermostat correctly seated

• Maintain a watertight seal

• Ensure correct operation of temperature switches

• Prevent coolant leaks and overheating

The aluminium construction makes this housing far more resistant to age-related failures than plastic alternatives.

Fitment

• Vehicle: VW Type 25 / T3 Syncro only

• Years: 1985–1992

• Engines: 1900cc & 2100cc petrol Waterboxer

• Cooling layout: Syncro

• Switch type: Screw-in switches only

Engine code compatibility

• DG: 1.9 (02/85 – 07/92)

• SP: 1.9 (08/86 – 07/89)

• MV: 2.1 (08/86 – 07/92)

• DJ: 2.1 (09/86 – 07/92)

• SR: 2.1 (08/86 – 07/92)

• SS: 2.1 (08/89 – 07/92)

O-ring seal (not included)

The thermostat O-ring seal is NOT included and must be purchased separately.

Related parts

• Thermostat including O-ring seal: 025121113F

• O-ring seal only: N90136802

Replacing the O-ring whenever the housing is removed is strongly recommended to ensure a proper seal.

Fitting notes

• Confirm your vehicle is a Syncro before ordering

• Ensure all temperature switches are the screw-in type

• Clean mating surfaces thoroughly before installation

• Tighten fasteners evenly to avoid distortion

• Refill with the correct coolant and bleed the system fully after fitting

A robust, OE-style aluminium upgrade that delivers reliable sealing, accurate temperature control, and long service life for Syncro Waterboxer cooling systems.