Oil Filters
Overpressurisation of Spin on Type Oil Filters
Normal
Overpressurised
High quality spin on type oil filters are designed to withstand oil pressures considerably in excess of the highest working oil pressures specified for modern engines. Engine manufacturers typically require that the oil filters withstand minimum pressures of 200 P.S.I. or over twice the normal operating oil pressures of most engines. While pressure resistance varies with size and gasket position, all ‘RYCO’ filters are guaranteed to meet this minimum requirement and the majority of types would have pressure resistance characteristics close to 300 P.S.I.
In spite of these large safety margins, filter overpressurisation and subsequent engine damage can and does occur; invariably as a result of malfunction of the engine’s oil pressure regulating valve. This valve is installed either as part of the oil pump assembly or less usually at an oil gallery location downstream of the oil filter. Its function is to control maximum oil pressure in the lubrication system and its operation is crucial in modern high speed oil pumps and engines. In the event of unregulated oil pressure any spin on oil filter will fail, beginning with the deformation of its body or shell and leading usually to eventual seal blow out. It is interesting to note that the release of system pressure occasioned by filter leakage or blow out may temporarily free the malfunctioning pressure regulating valve and thus give cause for the suspicion that the filter was faulty.
By measuring the extent of shell or body deformation, the filter manufacturer can quite accurately estimate the lubrication system pressure present just prior to failure. On all occasions of overpressurisation, it is in the interests of vehicle owners that the causes of pressure regulating valve failure be sought out and corrected so that the risks or re-occurrence can be eliminated.
Known causes of oil pressure regulating valve failure are as follows:
- Small and seemingly insignificant debris, varnish or rust on the valve cylinder or piston could occur after engine rebuild or major dismantling.
- Reassembly of a worn valve where the piston is repositioned at variance to its original wear track.
- Valve lock up as a first sign of glycol type anti freeze build up in the oil – a result of minor head gasket leakage.
- Hydraulic lock can occur with some valve designs and jamming by ice crystal formation can be experienced in cooler climates as a result of condensation build-up in the oil.
The risk of oil pressure regulating valve malfunction and subsequent filter failure can be lessened by regular oil change maintenance and adherence to the following checks:
- After engine or oil pump rebuilds or disassembly, ensure that the oil pressure regulating valve components are clean, undamaged and re-oiled prior to assembly. Ensure that the piston moves freely within its cylinder.
- When following normal practice of ‘checking for leaks’ on filter installation, ensure that maximum rated oil pressure is achieved through adequate engine revolutions.
Oil filter overpressurisations must be seen as a symptom of oil pressure regulating valve malfunction. While a rare occurrence, resulting engine damage can be severe and these descriptions are provided to enable adequate preventative measures to be taken.