Lockdown and filters

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Continuing his investigation into how lockdown affects everyday cars, Rob Marshall looks at why you can advise with confidence that low mileages do not mean filter replacement intervals can be stretched.

While the importance of fitting decent quality filtration is not lost on most technicians, having additional knowledge in your armoury will help you justify, to even the most sceptical drivers, that regular filter changes really are in their best interests.

Air Filter Replacement

Air filters

Quite clearly, air filter life is related closely to engine running time. Atmospheric conditions also make a notable difference; dusty environments, for example, will gobble-up filtration capacity remarkably quickly. Yet, what about inactivity?

MAHLE is one such brand that emphasises the OE quality of its parts, telling AT that its filters continue to operate efficiently should the vehicle be either left in the open, or used infrequently. UFI filtration agrees with Mahle’s additional advice that technicians should heed the manufacturer’s change interval. However, considering the current situation, it is likely that an air filter will need renewing way before the specified distance has been covered and it is worth remembering that some car makers recommend a two years’ replacement interval for low mileage users.

Yet, surely this means that air filter elements are not immune to the effects of time? Interestingly, not all quality manufacturers whom we approached were united fully with their recommendations. Like Mahle, the Bilstein Group told us that a car being laid-up has no effect on air filter life, whereas UFI advises replacing the air filter every 12 months, because the pleated cellulose filter media can absorb moisture over time, which reduces its filtration capacity. To address this, UFI highlights that it has been developing synthetic filter fibres that possess extra hydrophobic properties. First Line commented that, for cars that have not been moved for months, a technician might discover condensation, or even mould in the filter element in rare cases. Yet, First Line also points-out that the air box housing is not airtight and some air will still pass through the filter, even when the engine is not running. Therefore, the filter can still clog, albeit over a far longer period of time, because it is still performing its filtration role.

Valeo and Hella Hengst concur with UFI and First Line; as the pleats are made from cellulose, both air filter performance and physical characteristics are affected by atmospheric humidity levels. Valeo highlights that a quality filter manufacturer will take very high and low ambient temperatures into account during the developmental phases. A quality air filter will also not rot in its housing, because the filter is saturated with either acrylic, or phenolic resins. Hella Hengst explains that this impregnation also ages; technicians can spot this by looking at deformation in the filter as its strength is compromised. The resultant decrease in airflow will cause a host of issues, from excessive emissions and poor fuel consumption to an increase in engine wear.

Oil Filter Cartridge

Oil filters

As discovered in our separate engine lubrication editorial, even OEMs with the longest service internals recommend more frequent oil changes, when the engine spends much of its time operating below its optimum temperature. Interestingly, oil filters tend to be unaffected directly by multiple short trips; the effect of deteriorating oil quality is more relevant to their lifespan. The filter clogging risk rises not only with an increase in oil viscosity, as the lubricant oxidises, but also due to extra contaminations being present. As most engine wear occurs during the cold-start and warm-up phases, the oil filter might be faced with trapping a greater quantity of harmful particles in the event of multiple short runs.

As engine oil takes longer to reach its optimum temperature, compared with coolant, the driver might be unaware that the engine has not warmed fully. The Bilstein Group argues that, because short journeys and cold weather increase the water content within the crankcase, oil that remains relatively cool cannot permit these contaminations to evaporate.

The resultant oil/water emulsification can saturate the filter medium prematurely, highlighting the importance of the oil filter’s bypass valve. Naturally, if activated, lubricant still flows around the engine, albeit unfiltered. While this is undesirable, it is a preferred situation than starving the engine of oil. Furthermore, the issues associated with lockdown-style motoring highlights that decent filter capacity, bypass and anti-drain valves being to the correct specification, high-quality filtration medium and suitable anti-corrosion properties for metal canister designs are reasons why any garage should never fit less than OE quality filters.

Fuel Filter

Oil filters

As discovered in our separate engine lubrication editorial, even OEMs with the longest service internals recommend more frequent oil changes, when the engine spends much of its time operating below its optimum temperature. Interestingly, oil filters tend to be unaffected directly by multiple short trips; the effect of deteriorating oil quality is more relevant to their lifespan. The filter clogging risk rises not only with an increase in oil viscosity, as the lubricant oxidises, but also due to extra contaminations being present. As most engine wear occurs during the cold-start and warm-up phases, the oil filter might be faced with trapping a greater quantity of harmful particles in the event of multiple short runs.

As engine oil takes longer to reach its optimum temperature, compared with coolant, the driver might be unaware that the engine has not warmed fully. The Bilstein Group argues that, because short journeys and cold weather increase the water content within the crankcase, oil that remains relatively cool cannot permit these contaminations to evaporate.

The resultant oil/water emulsification can saturate the filter medium prematurely, highlighting the importance of the oil filter’s bypass valve. Naturally, if activated, lubricant still flows around the engine, albeit unfiltered. While this is undesirable, it is a preferred situation than starving the engine of oil. Furthermore, the issues associated with lockdown-style motoring highlights that decent filter capacity, bypass and anti-drain valves being to the correct specification, high-quality filtration medium and suitable anti-corrosion properties for metal canister designs are reasons why any garage should never fit less than OE quality filters.

Diesel filters

Diesel injection systems tend to be far less tolerant of impurities than those of petrol engines, hence why manufacturers pay more attention to the filtration aspects. Naturally, this demands that technicians do the same. As with petrol, diesel fuel oxidises if left within the tank for relatively long periods of time. Since 2011, pump fuel had to contain up to 7% bioethanol (hence the ‘B7’ label), which deteriorates faster than the alternative that is derived solely from crude oil. The result is greater quantities of gum and organic acids that can afflict the fuel filter. With the ‘eco’ bio-content providing both food and moisture sources, it is unsurprising that microbial growth promotes slime formation that also risks contaminating the fuel filter. Many of these issues tended not to have many consequences in pre-Covid times. Yet, with recent events making it more likely that fuel tanks do not receive a regular turnover of fresh diesel, expect to encounter such issues at service time, which you can help to prevent with more regular filter replacements. Should you notice slime within the filter canister, you may wish to recommend that owner considers a biocide fuel additive, such as that sold by Wynn’s.

Mahle and First Line acknowledge, however, that water contamination has always been an issue for diesel vehicles. This justifies why many fuel systems possess a water trap and a simple valve makes easy work of draining water from the canister. Yet, some of the latest designs are sealed, meaning that further dismantling might be required. A further consideration is that diesel fuel can solidify, should the vehicle be left standing for longer than six months. As neglected filters can block prematurely, due to all, or a combination of these factors, it is a wise idea to quote for a diesel filter change, even if the part was replaced only last year. Furthermore, as modern B7 diesel requires special care in storage, be extra vigilant if your customer tends not to use fuel station forecourts to refuel.

Diesel Filter

Cabin filters

When confronted with the technical facts, your customers might be persuaded that lower mileages do not mean longer filter replacement intervals. Yet, urging them that the cabin filter also requires annual replacement might be harder, because it is seen more of a comfort feature and is less critical than filters that protect the engine and fuel systems. Or is it?

Apart from the health benefits of enhancing air quality within the vehicle as much as possible, a clean cabin filter aids the demisting system’s efficacy. While the car has been standing, especially outside during the autumn and winter months, Valeo adds that the cabin filter can still degrade. Deposits, such as tree sap and leaves can still fall onto the vehicle and block the HVAC system. This can lead to moisture penetrating the cabin filter and spores from the resultant mould is hardly something that should be blown into the passenger compartment during a pandemic.

All of the suppliers that lent their technical advice for this feature recommend annual cabin filter replacements, irrespective of mileage. To help you communicate this message to customers, First Line has produced a dedicated poster, which you can request, by e-mailing marketing@firstline.co.uk with ‘Cabin Filter Poster’ as your subject. Do not forget to include your name and address in the message.

While replacing a cabin filter twice in the same year might be too much for some customers to stomach, it might be
a worthwhile recommendation for drivers that still cover high mileages. Mahle advises that early spring and autumn are optimum replacement seasons, because a new filter is more likely to capture the burgeoning levels of pollen in the spring; subsequent renewal in the autumn ensures that these contaminations are not clogging the filter and restricting airflow into the vehicle, when the driver replies on rapid warming and window defogging to keep safe.

Cabin Filter

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