What is Oil Filter Over Pressurisation?

Every now and then we’ll come across an oil filter that looks like someone’s tried to blow it up like a balloon. Sometimes they might even be leaking from the bottom seal or have a displaced seal. Despite how it may appear on the surface, this is not a sign of a poor-quality oil filter. Rather, a symptom of an underlying culprit within the engine. More specifically, over-pressurisation.

To understand over-pressurisation is, we first have to look at how oil circulates around the engine. When you first start your engine, the oil pump kicks in and draws oil from the sump. The pump then compresses the oil before sending it on its way. The oil then makes its way through the oil filter to be cleaned, and then through to all the main oil galleries to be distributed amongst all of the engine’s rotating and reciprocating components. 

The oil pump is driven by the engine’s crankshaft meaning flow is directly proportional to the speed of the engine. Most engine lubrication systems are designed to keep oil constant between 40-60 psi regardless of engine speed or temperature. This is controlled by a small component within the engine known as the oil pressure control valve.

The oil pressure control valve is commonly found as a spring-loaded plug and is located just after the oil pump impeller. It remains closed at low engine speeds and low oil viscosity, preventing oil from being drawn into the sump and directing it straight into the oil filter. As engine speed increases, so does the volume of oil being pumped through the engine. This causes the oil galleries and bearing to create a restriction in the lubrication circuit, which results in pressurisation. The spring within the oil pressure control valve determines the point at which the valve opens, meaning it controls the engine’s maximum oil pressure. 

Once the oil pressure reaches the point where it is greater than the force of the spring, the valve opens, allowing some of the oil to return to the sump, thus relieving some of the pressure. Who would’ve thought such a simple device could be responsible for such an important task?

However, as it is still a moving part, the oil pressure control valve is subjected to wear and tear over the course of the engine’s life. Over time, a groove can form on the valve housing and this generally occurs with the valve closed, causing the valve to become stuck. Poor maintenance with infrequent oil changes, contamination from engine coolant, or ice formation in extreme climates are some of the reasons as to why this might occur.

With the valve clogged, the engine oil exceeds its maximum pressure which in turn causes the oil filter to balloon, or worse yet, the seal to become displaced or the filter housing itself to split causing catastrophic loss of oil pressure and your engine calling it a day.

One crucial way to help prevent this from happening is to keep up with frequent oil and oil filter changes. This keeps things running clean inside your engine and help prevents carbon buildup within your oil pressure control valve. This is where Ryco comes in. Whilst pressure resistance varies with oil filter size and gasket position, Ryco oil filters are designed to withstand minimum pressures of 1379KPa (200 PSI) – twice the normal operating oil pressures of most engines, and a requirement for modern engine manufacturers.