GUD Spin-on filters are designed and constructed to withstand pressures greatly in excess of working pressures specified for various fitment applications. However, in spite of these large safety margins, filter over-pressurisation can and does occur. It is important to know that over-pressurisation does NOT occur as a result of a problem with the filter, but rather because of problems caused by the pressure regulating valve.
During normal operation, the oil pump draws oil through a strainer from the sump. Due to erratic pressure created by the oil pump at varying engine revolutions per minute (rpm), a pressure regulation valve, usually situated between the pump and the oil filter, maintains oil pressure within the system. At times of excessive oil pressure, such as high rpm or cold starts, the piston in the regulating valve is pushed back against its spring, allowing excess oil into the by-pass port and back into the sump. This cycle effectively controls oil pressure.
In an inoperative pressure-regulating valve, the oil filter is subjected to extremely high, uncontrolled pressure and will quickly show symptoms of over-pressurisation. Research has shown that regulating valves may become inoperative, or seize due to various factors. However, an extremely high percentage of valves malfunction shortly after engine overhauls, with chemical washing of engine parts and subsequent rusting, or dislodged dirt entrapment often resulting in valve seizure.
Once over-pressurisation stage has been reached, the subsequent sudden pressure loss is sometimes capable of freeing the valve, restoring normal oil pressure. Over-pressurisation therefore occurs only as a result of a pressure regulating valve seizure or malfunction, and not from anything relating to the filter’s performance.