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OIL FILTERS
General Information
As the length of car ownership extends maintaining a clean, well-running engine is critical. Changing the oil filter in a vehicle regularly is an essential part of this engine maintenance and one of the best ways to maximize this process is by selecting a Sogefi oil filter that is specifically designed to your vehicle needs.
What does it do?
Friction is created when machine parts move in relation to each other. In order to reduce this friction, which causes a reduction of efficiency and life of the machine, a lubricating oil-film needs to be created between the moving parts. To be most effective this lubricating oil needs to be clean of dirt and damaging particles - this is where the oil-filter comes in. If the contaminating particles are not adequately removed from the lubrication oil, and retained by the oil filter, they form together to create an abrasive paste that causes premature engine wear.
Apart from lubrication, the oil and the oil filter also have the following duties: Cooling: To absorb and transport heat created from the friction and engine heat Cleaning: To transport (to the filter) the contaminating particles created from wear and tear and remainders of the combustion process Sealing: The rings between liner and piston, simmering etc silencing of mechanical noises and the combustion process.
An ineffective or low quality oil filter is unable to perform such duties to the same standard as a specifically designed filter. Such failures can lead to major repair costs, which is why the FRAM brand slogan is; 'Pay a little now, instead of a lot later.
 
How does it work?
The oil pump, driven by the engine, aspirates the oil via a sieve (to prevent aspiration of large contaminants), from the cartridge, and pumps it to all the parts that need lubrication.
Oil filters can be designed as 'spin-on filters' or as 'filter-cartridges' in a housing. The former are replaced completely after their useful life whereas with the latter only the cartridge needs to be replaced inside the existing housing.
Full-flow filters
All the oil aspired by the oil pump passes through the oil filter before reaching the areas that require lubrication. Since the oil pump is directly related to the engine rpm, the oil pressure needs to be limited by an overpressure valve, incorporated in the oil pump itself. Usually this overpressure valve limits the pressure in the filter-lubrication-system to between 3 and 5 kg/cm2. |
 
If the pressure rises above this limit, there is an increased risk that the filter gaskets and seals are damaged or pushed out of their seatings. Sometimes, when the pressure rises too high and the overpressure valve in the oil pump does not open, the gasket of the oil filter can be blown out of its retainer causing the oil to leak out of the filter. High pressure can also cause the oil filter housing to start bulging. The oil filter then gets unjustly blamed for a problem caused by the overpressure valve in the oil pump. When the engine and the pump are cooled off (when repairing) the valve seems to be working normally again, eliminating evidence of the real cause of the problem. To prevent too big a pressure difference between the dirty and the clean side of the filter element, a by-pass valve is mounted in the filter. This valve opens at a pressure difference of 1 to 2 kg/cm2; this way (unfiltered) oil can still lubricate the engine, even with a completely blocked filter element.
Furthermore, an anti-drain valve prevents the filter from draining its oil back to the engine sump when the engine is stopped. In some cases, an anti-siphon pipe is present to avoid oil siphoning out of the filter when the engine is stopped. Pressure drop and filter-life (dust loading capacity) are designed according to the requirements of the original equipment manufacturer. Care must, therefore, be taken to fit a filter that meets these specifications, rather than any filter that 'will fit’, usually sold at a lower purchase price than a high quality filter.
By-pass aspirated/ combination filters
The oil aspired from the cartridge is pumped straight to the areas that need lubrication. However, in a line parallel to the main line, the by-pass filter is located where about 10% of the main oil flow is by-passed to be filtered. The by-pass ratio is calibrated by a fixed restriction in the by-pass filter.
Although the main oil flow goes unfiltered to the engine, the efficiency of the by-pass filter is very high.
In contrast to air filters which are 'single pass', an oil filter is a multi-pass' system (the same oil is repeatedly passing the same filter), thus, when a particle initially passes through the mainstream, next time it will be caught in the by-pass. As such, it takes longer for a by-pass system to catch all particles. Full-flow versus by-pass provide therefore the same level of protection for the engine. A combination of full-flow and by-pass filters is usually applied in the heavy-duty markets (diesel engines in truck-, industrial-, and earthmoving applications). About 90% of the oil is filtered through the full-flow filter whereas the remaining 10% returns to the sump via the by-pass filter. The result of this filter combination is a very good conditioning of the oil, whereby the life of oil and filter is increased dramatically.
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