Oil Pressure Relief Valve Screw - Type 4, Waterboxer (Hex Head Style)

This oil pressure relief screw upgrade kit replaces the original slotted oil pressure relief plug with a 19mm external hex-head plug, making removal and installation far easier—especially on engines that have seen years of heat cycles and rounded screw slots.

It is suitable for a wide range of Volkswagen engines, including Type 4 aircooled, aircooled Type 25, and 1900cc & 2100cc Waterboxer engines, making it an ideal upgrade during engine servicing, rebuilds, or when chasing oil pressure issues.

A major advantage of this version is the central threaded port, which allows the optional installation of an oil temperature sender, adding valuable engine monitoring without drilling or modifying the crankcase.

What this part does and how it works

The oil pressure relief system regulates maximum engine oil pressure. Inside the crankcase, the relief plug retains a spring and piston. When oil pressure rises too high—such as during cold starts—the piston opens against spring pressure, allowing excess oil pressure to be safely bypassed. This protects the oil cooler, seals, and internal engine components from damage.

This upgraded plug performs the same critical function as the original, but with:

• Easier servicing thanks to the 19mm hex head

• Optional oil temperature sensor fitment via the centre port

• Improved long-term serviceability compared to slotted plugs

Sensor compatibility (optional)

The centre port can be used to install an oil temperature sender:

• 1/8″ NPT tapered sender (e.g. V323057)

• M10 x 1 metric sender (e.g. V323423, requires sealing washer)

This makes it an excellent solution for adding oil temperature monitoring while keeping the installation neat and reversible.

Fitment

Baywindow Buses

• Type 4 aircooled engines

  • 1700cc

  • 1800cc

  • 2000cc

Type 25 / T3 Buses

• 1600cc aircooled (CT engines)

• 2000cc aircooled

• 1900cc Waterboxer

• 2100cc Waterboxer

Installation notes

• Torque setting: 20 Nm (15 ft-lb)

• Always inspect the relief spring and piston for wear or scoring during installation

• Ensure the bore is clean before refitting

• Use the correct sender type if installing an oil temperature sensor

Why upgrade to this version?

• Much easier removal and installation than the original slotted plug

• Ideal for engines with damaged or seized original plugs

• Allows clean installation of an oil temperature sender

• Suitable for both aircooled and Waterboxer engines

A smart, practical upgrade that improves serviceability, engine monitoring, and long-term reliability across a wide range of classic Volkswagen engines.