All cars are fitted with a bunch of different filters to keep the air and fluids that the car needs run nice and clean. The car you drive, at a minimum will be fitted with an oil filter, an air filter, a fuel filter and a pollen/cabin filter.
You’ll no doubt have been told that you have to change your cars filters when it gets serviced but why? What will happen if you don’t bother? Another thing to be aware of is that not all filters are the same, the quality can vary drastically and to the naked eye it can be difficult to spot a poor quality filter.

In this blog we’re focusing our attention on the most commonly changed filter, the oil filter.

How the oil filter works:
There are 2 main types of oil filter, the spin-on type and the cartridge/element type, they both do exactly the same thing, just in slightly different ways.

The function of the oil filter is to continuously clean the engine oil of minute carbon, soot and metallic particles that naturally break free from the moving engine components as you drive. If left unfiltered the engine oil would very quickly become ineffective and would actually start to do harm to your engine (imagine these particles being a bit like the exfoliant your wife uses in the bath – very abrasive and scratchy, not at all what you want in your engine!) These particles actually start to wear away the moving components inside your engine – in particular the bearings. Eventually the wear will become so great that the engine is likely to seize. If that happens you’ll either be looking for a new engine or a repair bill well into the thousands.

This diagram shows a cutaway of a typical ‘spin-on’ oil filter. The blue arrows illustrate the direction the oil flows around the filter.

The oil filter has a built-in safety mechanism in the form of the bypass valve. When the filter gets old and the filtration material gets clogged up with all these carbon and metallic particles the bypass valve opens up (at a predefined pressure) so that the engine still gets a constant supply of oil. The trouble is, the oil is now completely unfiltered.


The Difference Between a Good & a Bad Oil Filter:
The exploded view of the oil filter below illustrates all the separate parts that go into a high quality oil filter. Each component is made to the correct specification is made of the correct grade of material, as specified by the original vehicle manufacturer.

The comparison below illustrates clearly that not all filters are the same inside. The table compares an original Equipment Bobcat filter with some aftermarket competitors, it’s clear to see some are better than others. The most noticeable differences tend to be in the amount of filtering media used (the comparison filter in the middle has a fraction of the media used in the original filter and will therefore clog up much faster)
Less obvious, but most concerning is the strength of the bypass valve. Some filters are fitted with weaker springs in their bypass valves which will allow oil to flow straight through the filter, completely unfiltered!
But enough of the horror stories! there are plenty of excellent quality filter manufacturers out there that make their products to OE specifications and can still save you a load of money over the OE vehicle manufacturer branded filters. At MicksGarage we stock most of them so you can make your own decisions as to which brand you want to buy. Our advice is to do your research, find out what brand of filter was fitted to your car originally (vehicle manufacturers don’t make their own filters by the way – for example a BMW branded filter will be manufactured by Mahle, Mann or Knecht, not actually BMW).
Check out the video below for a more in-depth look at what goes on inside your cars filters:
Save 20% on all MANN filters this January with discount code JAN20

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  • ADVANCED FILTRATION

    Everything is very well explained, Collection of statistics is really good. Must say good article!!