On many modern vehicles, the pressure cap doesn't sit on the radiator at all. It sits on a separate expansion or header tank, which becomes the pressure-control point for the whole cooling system. The Tridon CY18125 is designed for exactly that job, screwing onto an M52 plastic neck to seal the tank and manage system pressure.
It's rated at 18 PSI (125 kPa), which lifts the coolant's boiling point well above what it would be at atmospheric pressure, giving your engine a healthy safety margin in heavy traffic, long climbs or when towing. The double-seal recovery design releases pressure as the coolant expands and lets it return as the engine cools, so the system stays full and free of air bubbles that can cause hot spots.
Plastic caps on expansion tanks sit right in the heat of the engine bay, and over time the seal can harden or the valve spring can weaken. If you're replacing a cracked or leaking expansion tank, it's a good idea to fit a new cap at the same time rather than reusing the old one. Always match the thread size and pressure rating of your original cap.
- Series - CY
- Pressure - 18 (PSI), 125 (kPa)
- System - Recovery
- Cap Style - Plastic
- Connection Type - Plastic Screw (Suits M52)
