Oil Leaking from Intake Pipes and Seals

A common problem is oil leaking from vehicles with less than 50,000kms, often caused by blocked catch can filters, incorrect fitment, or poorly designed products.

Excessive breathing, otherwise known as crankcase ventilation in diesel engines, creates oil vapour, which over time can saturate intake components. This weakens the rubber seals and pipes, causing oil to seep all over the engine bay. With proper diagnosis and maintenance, many of these issues can be prevented.

What Is Crankcase Ventilation?

When the engine is running, blow-by gases escape from the cylinder into the crankshaft cavity. These gases contain unburnt fuel and all the constituents of exhaust gas, which mix with the engine oil vapour. Due to the higher compression the diesel engine produces, a much higher crankcase ventilation is present than seen in petrol engines. However, excessively high positive crankcase ventilation is not normal; therefore, it is important that normal and excessive crankcase pressure are properly assessed.

To combat excessive crankcase ventilation, most diesels use a factory fitted catch can, otherwise known as Positive Crankcase Ventilation (PCV) valve. Unfortunately, many are not aware of this and servicing the PCV is often overlooked.

The good news is that if you’re adamant that your diesel must have a catch can, with the correct servicing and timely replacement of the catch can filter, they can be beneficial. However, this only serves to extend some of the additional service items for diesel engines.

Some of these maintenance items are not always clearly listed in manufacturer service schedules, but they remain important for long-term reliability.

Maintenance Items That Can Reduce Excess Engine Breathing

Cleaning of Turbo Intercoolers

The function of an intercooler is to assist with the efficiency of the diesel engine by cooling the hot air from the turbo before it enters the engine. This creates a better burn rate of the diesel. However, excessive oil combined with other internal debris trapped in the intercooler can greatly reduce this cooling effect.  While a catch can might be capable of removing some oil and vapour that is recirculating from the crankcase breather, it won’t prevent external debris or other contaminants. This includes air filter fibres and dust that unfortunately pass through air filters.

Periodic inspection and cleaning of the intercooler may be required as part of long-term diesel maintenance.

Removing Carbon from the Intake System

It is quite common to find a diesel intake system with excessive carbon buildup, which is a result of the Exhaust Gas Recirculation (EGR) system. This system plays a vital role in protecting the engine as it reduces harmful emissions. These emissions can pose significant risks to humans, such as cancer and respiratory problems. Therefore, the EGR system, along with the intake manifold, is essential for diesel maintenance and requires removal for thorough cleaning.

If carbon is found that wasn’t from the EGR system, this is an entirely separate issue. This may be caused by poor service history, incorrect oil, overfull engine oil, or an underlying issue such as an injector washer failure.

Regular Check and Adjustment of Valve Clearances

Excessive crankcase ventilation can be caused by worn cylinder head valves. These valves open and close, allowing air to enter the engine, mix with the diesel and in turn create combustion.  This process drives the pistons in an up-and-down motion, while another valve, known as the exhaust valve, opens, allowing the exhaust to escape. Valve clearances form part of routine diesel maintenance and can affect performance, emissions and crankcase pressure if neglected. They can become too tight or loose and overall affect performance, fuel economy and the life of the engine. Incorrect valve clearances can also cause DPF related issues.

Timing Chain and Belt Replacement

Replacement of timing chains or belts at correct intervals is important for maintaining accurate engine timing and reliability. The procedure requires precision to avoid misalignment of key components. A stretched timing chain can also cause DPF and other reliability issues.

Injector Washer Replacement

Injectors fitted to most of the modern diesel engines, predominantly common rail diesel, are mounted beneath the rocker cover. They use a removable seal between the cylinder head and the injector to help seal the combustion chamber from leaking gases. Several manufacturers recommend regular interval replacement of these washers. If they fail, the engine compression leaks past these washers and results in increased crankcase ventilation. This, in turn, also releases significant amounts of carbon into the crankcase, causing carbon in the lubricating oil. This will eventually reach the point of exiting the breather and entering the intake system.

Modern diesel engines are engineered with integrated crankcase ventilation systems. Adding aftermarket components changes airflow and pressure characteristics within that system. Without understanding the cause of excessive breathing, modifications can create unintended consequences.

✅ Pros of Catch Cans

• Can reduce oil vapour entering the intake system

• May help keep intercoolers cleaner

• Can reduce visible oil mist in some engines

❌ Cons of Catch Cans

• May mask underlying mechanical faults

• Blocked filters can increase crankcase pressure

• Incorrect installation can create new leaks

• Do not address root causes of excessive engine breathing