Radium Catch Can Kits for the Ford Fiesta ST: Your PCV Questions Answered

The Fiesta ST is one of the great boost-for-the-money hot hatches, and its 1.6 EcoBoost rewards anyone willing to look after the oily side of the engine. The catch is the positive crankcase ventilation (PCV) system. Under boost, oil mist and vapour from the crankcase get pulled into the intake tract, where they coat the intercooler, the intake valves and the combustion chamber. Left alone, that does nothing good: reduced octane margin, detonation risk on a mapped car, and slow carbon accumulation.

A catch can interrupts that path and traps the oil before it reaches the intake. Below are the questions Fiesta ST owners ask us most before ordering - answered straight, with no filler.

WHAT DOES A PCV-SIDE CATCH CAN ACTUALLY DO ON A FIESTA ST?

The PCV-side kit sits in the circuit that vents crankcase pressure back into the intake. As blow-by gases travel through it, oil mist condenses and drops out of suspension into the can, while the remaining gases carry on to the intake.

On a stock Fiesta ST, that means less oil coating your intercooler and charge pipes. On a mapped or big-turbo car running more boost, blow-by rises with cylinder pressure, so the can is working harder and earning its place. The Radium Catch Can Kit PCV, Ford Fiesta ST is a direct-fit kit built around this exact circuit, so you are not adapting a universal can to a specific engine bay.

WHEN IS A DUAL CATCH CAN KIT WORTH IT OVER A SINGLE PCV KIT?

The Fiesta ST has two ventilation paths: the PCV side, which handles the bulk of normal running, and the crankcase breather side, which comes into play under load and boost. A single PCV kit covers the first path only.

The Radium Dual Catch Can Kit, Ford Fiesta ST captures both circuits. If your car sees regular track days, hard road use, or a larger turbo, the breather side is pulling meaningful vapour under boost, and a PCV-only setup leaves that oil heading for the intake. Dual kits are the tidier answer for anyone who wants the whole ventilation system handled once, rather than adding a second can later.

HOW OFTEN DO I NEED TO DRAIN THE CAN?

There is no fixed interval - it depends on how hard you drive and how healthy the engine is. A useful starting routine is to check the level every 1,000 miles or after each track day, then adjust to what you actually collect. A healthy engine under normal road use might put a small amount in the can over an oil-change interval. A tired engine or a heavily boosted one will fill it noticeably faster.

Get into the habit of checking it whenever you check oil and coolant. Run the can too full and it can back up and stop doing its job, so treat the drain as part of your normal fluid check, not a job you do once a year.

WILL A CATCH CAN AFFECT MY MOT OR ROAD LEGALITY?

A correctly fitted catch can is a closed system - it captures vapour, it does not vent crankcase gases to atmosphere. In the UK, the MOT looks at emissions and visible smoke, and a sealed, properly plumbed catch can does not change how the engine burns fuel or what comes out of the tailpipe.

What matters is fitment. Route the hoses as the kit intends, keep the system sealed, and make sure nothing is left open to atmosphere. Fitted properly, a catch can is a supporting modification, not something that fails a test.

WILL THE KIT THROW A CHECK ENGINE LIGHT?

A properly installed kit on the correct circuit should not trigger a fault. The issues come from poor installation: leaving a vacuum line disconnected, introducing an unmetered air leak, or plumbing the can into the wrong hose. Radium's Fiesta ST kits are designed for the factory circuits, which is exactly why we stock the vehicle-specific kits rather than a generic can plus a pile of adapters.

Take your time with the hose routing, check every connection is seated, and you should see no new codes.

DOES IT HELP WITH CARBON BUILDUP ON THE INTAKE VALVES?

It reduces one of the two main contributors - oil vapour from the crankcase. The other contributor is EGR, which a catch can does not address. So no, it is not a cure-all for intake valve deposits on its own.

What it does is stop you making the problem worse. For Fiesta ST owners who intend to keep the car long term, capping the oil vapour path early is far easier than dealing with a coked-up intake later. Think of it as prevention, not a cleaning service.

IS FITTING A CATCH CAN KIT A DIY JOB?

For most hands-on owners, yes. The vehicle-specific kits come with what you need for the Fiesta ST engine bay, and the work is hose routing and bracket mounting rather than engine surgery. If you are comfortable doing your own oil changes and working around the intake tract, you can fit one on a driveway.

If you would rather not touch the PCV system yourself, any competent independent workshop can do it in an afternoon. Either way, use the correct kit for the platform - that is the difference between a clean install and a weekend of adapters and leaks.

WHICH RADIUM KIT SHOULD I ORDER?

Two straightforward rules of thumb:

• Road-driven, lightly modified Fiesta ST, primarily worried about intake oil: start with the PCV-side kit.
• Track use, big boost, or you want the whole system covered in one go: go dual.

Both kits are available on our store, and as an authorised Radium Engineering dealer we ship genuine parts with correct fitment straight to UK addresses. If you are unsure which suits your build, tell us what you are running and we will point you at the right part number.

THE SHORT VERSION

A catch can on a Fiesta ST is not a gimmick - it is cheap insurance for your intake, your intercooler and your tune. The PCV-side kit handles the everyday circuit; the dual kit handles everything the boost throws at it. Check and drain it on a routine, fit it properly, and it will quietly do its job for the life of the car.