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Filtering out the harm

By autotech-nath on October 30, 2021

Ineffective filtration presents many negative consequences to the modern motorcar. Owner neglect, poor quality parts, incompatible fitments and even technician error can be responsible, leading Rob Marshall to probe the issues a little deeper.

Oil filters…

Unless you embark on an engine strip, it is pretty difficult to assess the damage caused by a clogged, or low-grade oil filter. Yet, the consequences of sharp metal particles being pumped to rotating parts are well understood.

What is not so well appreciated is that most engine wear occurs during and immediately after a cold start. The importance of an anti-drain back valve in a quality oil filter helps to ensure that lubricant reaches critical components as soon as possible. The tell-tale rattle, which disappears soon after the engine has fired after several hours standing, is a potential sign that a low-quality (or incorrect) oil filter is fitted.

While engine oil degradation rates increase, the oil filter also suffers if the car is subjected mainly to short, low-speed journeys. First Line reports that, should these drive cycles persist, even a quality element can clog prematurely. The company advises annual replacement in such scenarios.

Oil leaks tend to be the consequences of fitting errors. UFI Filters highlights that incorrect techniques include using inappropriate tools, not cleaning (or oiling) gasket surfaces and poor installation that results in crushed, or twisted, O-rings. Additionally, because most canister-type filter housings are made from plastic, heed the tightening torque that is supplied either in the technical literature, or stamped on the moulding.

Air filters…

Logically, Blue Print highlights that ineffectual air filtration has ramifications for the oil filter, too. Aside from abrasive particles passing through the air intake and damaging the piston/rings, cylinder walls and valves, they can end up in the crankcase. It is also mind-boggling to think how much air passes through a typical air filter throughout its lifetime, especially with turbocharged engines. Blue Print reports that an air filter on a 1.6-litre 2012 Nissan Qashqai would have filtered 40 million litres of air by the time it reached its recommended 37,000 miles replacement interval.

Even so, you may discover an excessively dirty air filter that has not reached its official renewal mileage. Trust your instincts and advise the customer. First Line finds that some car owners resist replacing air filters, because the car has not covered sufficient miles. This means that you will need to make the case that virtually every car manufacturer recommends more frequent air filter replacement, dependent on atmospheric conditions. Aside from poor engine running and difficult starting, make a case for economy: a clogged air filter increases fuel consumption and emissions. In addition, air filter condition is one of the primary initial checks that informed garages make, when investigating DPF blockage causes.

The relative ease of replacing air filters can lure technicians into a false security; mistakes still happen. UFI reminds us that not ensuring that its foam edges seal correctly in the housing can affect the filtration ability, as well as causing a noise. After you extract an old filter, even if it is to be refitted, remove any larger particles from the housing, such as leaves. Consider also that engines prefer to inhale colder, denser air. Therefore, ensure that any ducts, leading to the car’s front, are connected to the airbox. This may lead you to advise performance air filter enthusiasts to reinstate any removed air filter housings and associated pipework, because it could make the engine run better. Interestingly, UFI highlights that cleaning standard filter pleats with compressed air is inadvisable, because doing so increases the material’s porosity, therefore compromising its filtration abilities.

Petrol filters…

As many petrol cars do not possess fuel filters, it is easy to overlook the models that have them fitted. First Line adds that replacement can be deemed incorrectly as an unnecessary expense. Yet, the recent introduction of E10 petrol is confronting petrol filtration with new challenges. As ethanol is an effective cleaner, it can loosen residual petroleum deposits (such as gums) within the fuel tank, enhancing the risk of them being introduced to the fuel injectors. Therefore, should you be confronted with a car that possesses a replaceable petrol filter, consider advising the owner to have it replaced as soon as possible. Many of these units tend to be slung beneath the car, exposing them to moisture and road salt. The unions are vulnerable to corrosion, too, particularly if the filter is overdue for replacement. As these metal unions can incorporate the entire fuel line, breaking them is clearly undesirable, so work carefully. Even so, quality manufacturers protect petrol filters, by either making them from plastic, or painting the canister in anti-corrosion paint. Yet, consider that the coating will be compromised, should the filter body rub against any surrounding metal parts. Ensure, therefore, that any plastic, or rubber, mountings are intact and refitted correctly. When fitting a replacement, most types tend to be directional; a printed arrow on the filter body tends to indicate the flow path from the tank to the engine, not vice versa.

Especially as E10 petrol increases the risk of fuel system blockages, garages need to suspect the fuel filter, should they encounter a petrol car with engine running issues and low fuel pressure faults. Typical symptoms include difficult starting and power losses, because the quantity of fuel delivered is lower than that requested by the engine. Blocked injectors and engine stalling are further consequences. MEYLE emphasises the importance of buying quality, elaborating that it has found low-quality filters to be so bad that the fuel is not even filtered after passing through the canister, making the quality argument even more relevant.

Diesel filters…

As diesel fuel contains up to 7% biofuel (hence the B7 designation on forecourt pumps), it is also not immune from the downside of ‘going green’. Bacterial growth is the problem. Blue Print reports that the waste products of the fungi contaminate the fuel, clogging the fuel lines. It recommends that the solution is regular diesel filter replacement.

The rate at which the fungi can develop within a diesel fuel system can be alarming. The reason is down to the system providing ideal conditions for the bacteria to grow. Its ‘food’ is provided by the bio-diesel, warmth by the engine and high- pressure pump, and moisture – mainly from condensation within the fuel tank. Blue Print reports that, without the correct filtration, the water content can corrode the pumps and fuel injectors. It adds its diesel fuel filters use a hydrophobic coalescing material that traps the water, while allowing the diesel to pass. The separated water forms droplets that collect at the bottom of the filter canister, which should be drained at service time.

UFI finds that typical workshop errors include not cleaning housings properly, locating hoses and connectors incorrectly and not using the correct torques (a consequence of which is pictured). It also emphasises inadequate bleeding techniques. Perhaps this is the most serious error, because of the negative impact it has on the expensive high-pressure fuel pump. Should the car, on which you are working, not possess a priming bulb, consider that bleeding may have to be performed diagnostically. Attempting to ‘cheat’, by cycling the ignition with the engine off, tends to be unfruitful, because the ECU will recognise this and not energise the pump. AT will look closer at the bleeding operation in a future article.

Cabin filters…

Restricted access aside, fitting replacement cabin filters is fairly straightforward – although it can be easy to overlook that many types require aligning with the airflow direction. First Line reminds us that all filters should be replaced in line with the vehicle manufacturer’s schedule and cabin filters need replacing annually, at least. Technically, a clogged filter can make the blower motor work harder, demanding more current and overheating either the motor unit and/or its speed resistor pack.

Consequences for the vehicle occupants of reducing the quantity of clean air available within the cabin include increased misting on the glazing and greater quantities of dust. Through its Borg and Beck brand, First Line offers free posters to help convey these messages to drivers, which can be ordered online:

Even so, aside from not serving the individual needs of their customers, perhaps the main consequence of not understanding cabin filters fully is missing the upselling and profit opportunities. Cabin air filtration has evolved since their widespread introduction in the 1980s, meaning the term ‘pollen filter’ is no longer strictly appropriate. While the basic specification still prevents dust, insects, seeds and pollen from entering the interior, carbon-activated filters capture impurities, such as those that cause odours and even pollutants. This latter ability is evolving further. The MEYLE-PD cabin filter extracts incoming NOx emissions, making it an ideal upsell to customers that drive mainly in cities, for example. There is also growth in filters containing biocides, such as UFI Filters’ ‘ARGENTIUM’ range, which was launched earlier this year. As reported in AT earlier in 2021, Honda dealers are retailing cabin filters that capture viruses, including COVID-19.

Transmission filters…

While we plan to look at more bespoke filtration applications in the future, many garages are performing automatic transmission fluid replacements, including investing in the necessary training and hardware. However, certain transmissions possess filters that require cleaning, or replacing. Their replacement costs can be eye-watering, especially when ordering them via a main dealer parts counter, but consider that aftermarket brands (such as Blue Print) are expanding their ranges.

As modern Continuously Variable Transmissions (CVT) rely on a steel belt running on steel pulleys, they tend to be more prone to producing abrasive metal shavings, compared to more conventional epicyclical geared automatics. Naturally, these contaminations are transported around the transmission by the oil, a consequence of which is irregular transmission operation, at best. Therefore, highlighting semi- regular oil and filter replacement intervals of around 30,000 miles is a wise recommendation.

Certain versions of Jatco transmissions that are fitted to Nissans, for example, possess a replacement filter in the side (as pictured) but it is also recommended to drop the sump, replace the filter within the oil pick-up assembly and clean the magnetic filters of swarf all before renewing the oil.



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