Why Your Modern Diesel Needs a Catch Can

Modern diesel engines are engineered to meet strict emissions standards, and one of the ways they do this is by recirculating crankcase blow-by gases back through the intake system. The problem? Those gases carry oil vapour — and over time, that oil coats the inside of your intake manifold, intake valves, and intercooler, hardening into a carbon crust that chokes airflow and kills performance.

What Is Blow-By and Why Does It Happen?

Every internal combustion engine produces blow-by — combustion gases that slip past the piston rings and into the crankcase. In older engines, this pressure was simply vented to atmosphere. Modern diesels use a Positive Crankcase Ventilation (PCV) system to route these gases back into the intake to be re-burned, reducing emissions.

The issue is that blow-by gas isn't clean air. It carries atomised oil from the crankcase. When that oil-laden air hits the intake, the oil settles on cold metal surfaces and slowly bakes into carbon. On diesels fitted with EGR (Exhaust Gas Recirculation), the problem is compounded — soot from the EGR mixes with the oil to form a thick, tar-like sludge that builds up layer after layer.

What Happens If You Don't Run a Catch Can?

Over tens of thousands of kilometres, the carbon build-up causes a range of issues:

• Restricted airflow through the intake manifold, reducing power and fuel economy
• Sticky intake valves — on direct-injection engines, there's no fuel washing over the valves to keep them clean, so carbon accumulates rapidly
• Intercooler contamination, reducing its ability to cool intake air and therefore its density, which directly impacts power output
• Increased stress on turbocharger seals, potentially leading to premature wear and oil leaks

In severe cases, the carbon build-up is so bad the intake manifold needs to be physically removed and cleaned or replaced — a labour-intensive and expensive job that could have been prevented with a catch can fitted early in the engine's life.

Not All Catch Cans Are Equal

There are two main types of catch can on the market: filter-type and baffled-type. The difference matters more than most people realise.

Filter-Type Catch Cans

Filter-type catch cans use a mesh or filter element to trap oil from the blow-by gas. They're cheaper and widely available, but they have a critical flaw: if the filter becomes saturated or blocked — and it will, because most people forget to service them — the crankcase pressure has nowhere to go. In the worst case, that pressure forces oil past the rear main seal. A rear main seal failure is an engine-out job that costs thousands. We've seen it firsthand, and it's the reason we stopped fitting filter-type cans entirely.

Baffled Catch Cans

Baffled catch cans use a series of internal baffles to slow the air stream and allow oil to condense and separate from the gas. There's no filter element to block, so crankcase pressure always has a path through the system. The separated oil collects in a reservoir that you drain at service intervals — typically every 5,000 to 10,000 kilometres depending on your driving conditions.

This is why we exclusively fit baffled-design catch cans. The risk of a blocked filter causing engine damage simply isn't worth the saving of a few dollars.

When Should You Fit One?

The best time to fit a catch can is when the engine is relatively clean — ideally from new or at low kilometres. The sooner you fit one, the more build-up you prevent. The second best time is now. Even if your engine already has carbon accumulation, a catch can will stop it from getting worse and protect your intake system going forward.

If you're buying a used diesel, it's worth having the intake inspected before fitting a catch can. If there's significant build-up, a clean may be recommended alongside the installation.

Our Recommendation

We recommend and primarily fit HPD catch cans, which use a proven baffled design and are vehicle-specific with proper mounting brackets, hose routing, and drain provisions. However, we're happy to fit other baffled-design brands if you have a preference — the critical requirement is that it uses a baffle system, not a filter.

A catch can is one of the cheapest forms of insurance you can fit to a modern diesel. For a few hundred dollars, you're protecting your intake, your turbo, and your engine from a failure that costs thousands to fix. If you're running a modern diesel — especially one used for towing, touring, or in stop-start traffic — it should be near the top of your accessory list.