How to choose an oil catch can for turbo engines

Turbocharged engines breathe hard. Under boost, combustion pressures climb and a small but steady stream of combustion gases slips past the piston rings into the crankcase — a phenomenon called blow-by. A catch can intercepts that oily vapour before it recirculates back through the intake, keeping carbon deposits off your intercooler, intake valves and throttle body.

In Australia, where turbo-diesel utes like the Ford Ranger, Toyota Hilux and Volkswagen Amarok dominate the work ute market, blow-by is an everyday reality. Drivers in Adelaide, Perth or western Queensland who regularly tow caravans or haul heavy loads spend long hours at sustained boost, which accelerates oil vapour production. A well-chosen catch can keeps the intake tract cleaner for longer and helps protect engines already worked hard in our climate.

Why turbo engines fight blow-by harder than naturally aspirated ones

A turbo pressurises the inlet charge. Higher manifold pressure increases cylinder pressure on the compression stroke, which forces more unburnt gases past the rings. Petrol direct-injection engines, common in Australian-delivered Commodores, Falcons and modern performance cars, are particularly prone because fuel no longer washes the back of the intake valves, so any oil that gets through tends to bake on as hard carbon.

Most factory PCV (positive crankcase ventilation) systems reroute these gases straight back into the intake. The idea is sound — they rejoin the combustion process rather than venting to atmosphere — but in a turbo car the vapours reduce detonation margin, foul intercooler fins and slowly choke the throttle plate. A catch can interrupts that loop, dropping the oil out and letting only clean air pass onward.

The three main catch can designs

Catch cans fall into roughly three families, and the type you pick shapes how they perform.

A simple baffled can uses internal plates or a labyrinth to slow vapour and let oil condense and drip into the reservoir. These are compact and easy to mount in the cramped engine bays of cars like the Hyundai i30 N or a WRX, where space near the firewall is tight. They handle street use comfortably.

Coaxial cans pass vapour through stacked tubes or a centre probe, forcing droplets to collide and separate. They are more efficient than basic baffled designs at higher RPM, which matters if you do plenty of highway driving between Sydney and Brisbane or spend weekends at track days at Wakefield or Phillip Island.

Filtered or breather-equipped cans add a small outlet that vents residual clean air to atmosphere or back to the intake pre-turbo. They suit cars running methanol injection or high-boost setups where re-introducing any unfiltered air downstream of the mass airflow sensor is risky.

Sizing capacity to your engine and driving style

Bigger is not always better. An oversized can mounted low in the engine bay sits in radiant heat from the exhaust or radiator, warming the contents and reducing how much vapour condenses. Likewise, a tiny can fills quickly and either needs constant emptying or blows back into the PCV line.

A practical rule is roughly 300 to 600 ml capacity for a four-cylinder turbo, scaling towards a litre for a six-cylinder like the Barra in a tuned Falcon. If you commute daily across Melbourne's outer suburbs with short stop-start bursts, the larger end of the range means less frequent draining. If your car lives mostly at wide-open throttle on country roads through regional NSW, smaller is fine because the oil stays well above ambient. Side-by-side ratings of popular units are listed in this oil catch can comparison guide, which pairs capacities against typical fitment notes.

Consider also where the ports sit. Top-feed and bottom-feed designs handle condensation differently. Bottom-feed cans let gravity move collected oil back towards the PCV when the engine is shut off, reducing slosh on the first few cold starts — a real benefit for owners who rarely let the engine fully warm through.

Build quality and what to look for in fittings

Reputable cans are either anodised aluminium or polished stainless. Aluminium keeps weight down, useful in a hot hatch where every kilogram matters, and dissipates heat quickly. Stainless resists corrosion longer, which is a plus for coastal owners in places like the Central Coast or Geraldton where salt air eats anything it can.

Pay attention to the inlet and outlet threads. Many cheaper cans use proprietary barbed fittings that only mate with their own hoses, locking you into one brand. AN-06 or AN-08 thread options are more flexible and match the aftermarket fittings already fitted on most turbo kits sold through Australian performance shops. The hose itself should be oil-resistant silicone or Viton-lined rubber. Standard vacuum hose hardens quickly under bonnet heat and sheds particles into the intake.

A drain tap is worth the extra dollars. Without one, you end up unbolting the can every few thousand kilometres to empty it — manageable on a weekend car, annoying on a daily driver.

Installation, plumbing and the legal side

Routing the PCV line through a catch can usually means cutting the factory hose and adding two new lengths with hose clamps. Most installs take two to three hours in a home garage and require only basic spanners, a step drill and a catch pan. For vehicles still under factory warranty, check with the dealer first — fitting a catch can on a new Ranger or Hilux rarely voids a powertrain warranty, but anything visible under the bonnet can complicate a future claim if an unrelated issue arises.

Australian Design Rules do not specifically address aftermarket catch cans, but a can that vents visible vapour to atmosphere may attract attention at a roadworthy inspection in states like Victoria or Queensland. Running a closed-loop setup — inlet from the PCV, outlet back to the intake — keeps the car compliant and indistinguishable from factory under the bonnet. Local performance workshops in suburbs like Clayton or Welshpool will often supply and fit a compliant unit for a few hundred dollars.

Cleaning intervals and long-term maintenance

Plan to drain and rinse the can every 5,000 to 10,000 kilometres, more often if you do frequent short trips where the engine rarely reaches full operating temperature — a common pattern for urban commuters in wintery Melbourne or Hobart. A neglected can will eventually saturate and start re-introducing oil back into the intake, undoing its own job and leaving thick black sludge at the bottom.

Drain the oil into a sealed container and dispose of it at a local collection point rather than tipping it down a household drain. Most Repco and Supercheap Auto outlets accept used engine oil for recycling, alongside many service stations.

Start by grabbing a tape measure and checking the diameter of your factory PCV hose, then count how many inlet and outlet ports the engine actually has. Those two measurements quietly decide which catch cans will physically fit and which are ruled out before any money changes hands.