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Proper air cleaning is absolutely vital.


Correctly designed and fitted engine air intake filters ensure the cleanest possible air flows into the engine. It is imperative that this charge air has the least amount of particles possible. Contamination can cause increased engine wear, a reduction in engine performance and vehicle downtime. 




We learnt the hard way about the real-world importance of air filtration when our LandCruiser ute suffered ‘dusting’, caused in part by an ill-fitting air cleaner element. An important rubber sealing ring had been accidentally misplaced during air cleaner element replacement and that allowed unfiltered air to get around the element and into the engine.

It took some time for the effects to manifest themselves, but eventually the engine needed a teardown and the worst was revealed: scored bores were obvious and subsequent dismantling showed big end and main bearing scoring as well. The only cure was a complete recon job.

As little as 100 grams of silica ingested into a diesel can cause a noticeable drop in engine performance, ‘blow-by’ pressure in the crankcase and increased oil and fuel consumption.

The best protection for an engine from dust ingestion is a high-set air intake – to minimise the entry of dust particles – and an appropriate, well-fitted air cleaner element. In high-dust environments a pre-cleaner may also be required.


A 100-gram siica gel packet shows how small a volume of dust is needed to kill an engine


Elements and servicing

When it comes to air intake filters, OEM engine makers and filter suppliers suggest dry air intake filters, rather than oiled-foam, after-market options. 

Those of us with grey – or no – hair can remember oil-bath air cleaners, in which oil-coated wire gauze was employed to capture dust particles. When the modern dry air filter was developed we sighed in collective relief, because it filtered more efficiently, never ‘dried out’ and was easy to inspect and replace.

Dry media typically gives the optimum combination of high efficiency, low initial restriction and long life, according to filter specialist Donaldson. The company says that oiled filter elements have the potential to provide long filter life, but some have issues with overall particle separation efficiency.

Our real-world experience with sticky-oil foam filters showed that surplus oil ‘migrated’ into the inlet piping, coating the inner walls with a sticky residue. We don’t know what the long-term effects of that would be on airflow sensors, intercoolers, turbochargers and inlet valves.

Another issue is that a sticky-oil filter has an open-pore foam medium that relies on the optimal oil content for filtration efficiency. If the oil dries out, or is absorbed by dust particles, filtration ability is greatly reduced or non-existent. In contrast, a neglected paper filter clogs with dust, but doesn’t allow dusty air into the engine.

An advantage of sticky-oil foam filters is that they can be washed out and re-oiled, but care needs to be taken, to avoid damaging the plastic pores. In the case of dry filter elements it is always recommended by engine OEMs and filter suppliers to replace filters rather than clean them.

We suspect most people have done it: tap a dusty air cleaner element against a tyre, or blast it ‘clean’ with an air hose. However, filter makers strongly urge against these practices, because there’s a risk of damaging the filtration media, or causing separation of the filter media from the filter end caps.

Some dry air cleaner elements can we washed, but this needs to be done with great care.

Filter makers also point out that many owners ‘over-service’ air cleaner elements. A fine layer of dust on the element is actually beneficial in achieving optimal air cleaning and helps it filter air more effectively than a brand new element does.

An air filter restriction indicator or dashboard gauge is a much more reliable way of knowing when a filter needs replacing than does a visual inspection. Every time an air cleaner can is opened and closed there’s a risk of filter misalignment or damage, as well as the risk of dust entering the engine inlet.

An air cleaner can that regularly holds a lot of dust and debris is a clear indicator of the need for a larger air cleaner and a pre-cleaner.

Meticulous care is needed when fitting any new element, to ensure that the gasket surfaces are clean and everything mates precisely. Improperly mated or damaged gasket seals are among the major causes of engine dusting.

At the same time, it’s wise to check all pipe unions and clamps between the air cleaner housing and the engine air inlet. Turbocharger suction will pull unfiltered air through any gaps in that plumbing.

The ‘flat-panel’ air cleaner elements used in virtually all new diesel utes and wagons are well known for being difficult to seal tightly. Well publicised LandCruiser V8 diesel engine dusting incidents have resulted in an after-market range of metal-box air cleaner housings, to replace the warp-prone standard plastic ones.


Dust on the engine side of the air cleaner is a sure sign of ineffective air cleaning


Fortunately, light 4WD truck air cleaner cans are much larger and seal more effectively, but plastic ones age and may not be as long-lived as steel ones.



Don’t ‘sock’ an air intake



An important part of any pre-cleaner design is that it doesn’t create an obstruction to the incoming air, even if its dust collection chamber is full.

Some 4WDers have theorised that if a pre-cleaner is desirable to keep excess dust out of the main air cleaner element, why not use a screen of some sort on a non pre-cleaning snorkel scoop?  

They opted for ‘socks’ made of simple cloth, or foam plastic soaked with sticky oil, to act as dust-screening pre-cleaners.

The one major problem with this ‘solution’ is that these socks can clog up with dust and insects that restrict airflow into the engine. The ‘strangling’ effect on air flow into any engine can cause a loss of power and excessive fuel use. It’s also likely to cause turbo overheating.

Another quite nasty and dangerous situation can occur if the sock is rinsed clean with petrol; we’ve heard of an engine ‘runaway’ when petrol fumes sent the engine revs soaring!

The best way of keeping dust out of an air cleaner element is by not driving in other vehicles’ dust clouds. If you can’t avoid prolonged driving through clouds of dust, fit a proper cyclonic-type pre-cleaner.



A 4WD is not a boat


There’s a belief that a high-mounted intake provides ‘water-proofing’, allowing a 4WD to ‘wade’ through deep water if necessary. That’s true, to some extent, but it’s important to check your inlet trunking to see if water could be sucked in.



The classic possible water entry point is the vacuator –  ‘flapper’ – valve fitted to some air cleaner canisters. It’s a rubber venturi that’s held closed by engine suction, but opens when the engine isn’t running. It’s placed at the bottom of the housing to allow dust and dirt particles to drop through the valve, when the engine is switched off.


Low-slung air cleaners on 4WD light trucks are at risk during water crossings


If that valve is under the water surface during a wading exercise and the engine stops for any reason, water can find its way into the air cleaner canister. That water may be ingested by the engine when it restarts and a cupful may be enough to cause ‘hydraulic’ engine damage.


An ‘old fashioned’ Toyota 75 Series air cleaner canister, purpose designed for off-roading, has a sealed debris container at the bottom, not a vacuator valve.


Wading preparation involves taping up any possible points of water entry, including vacuator valves.

Donaldson states that vacuator valves aren’t ‘set and forget’ items. People often believe that these are water drains and assume that regardless of the valve being hard, split, cracked or missing, that the water will still drain.

When the engine is under load, increased vacuum in the air-intake system sucks the valve closed, preventing dirty air from being drawn in, maximising pre-cleaning efficiency in cyclonic-type air cleaner housings.

At idle, there will be a pulsing effect on this vacuum, causing the vac valve to open and close rapidly, expelling accumulated dust. Upon shut down the valve opens, dropping separated dust from the housing, effectively making the filter housing ‘self-cleaning’

An inoperative or missing vac valve won’t disable the air cleaner, but will allow dusty air to enter the housing from the wrong direction, thus loading up the air filter element. Filter life in very dusty environments can be shortened by up to six times.


It’s impossible to overstate the importance of correct air cleaner selection and maintenance!




























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