Toyota 2H Oil Pressure Problems

The Toyota 2H engine is an old girl by today’s standards, but this popular engine from the 1980s was used in Landcruisers, Dynas, Coaster Buses, and many industrial applications. It may be an engine that is over 30 years old, but there are still quite a few getting around, and there is a technical issue that owners should be aware of.

There is a pressure relief valve that is located near the oil pump, which can get stuck due to debris or general wear & tear, which can cause a pressure spike in the system. This may cause the oil filter to expand and even fail in some circumstances. It is easy to blame the filter as the part that has failed, and from outward appearances, this is exactly what it looks like, but the cause of the failure is not the filter but a faulty pressure relief valve. The pressure relief valve may seem to be okay from an outward inspection, but it is the cause of most failures of this kind.

To resolve this issue, you will need to either clean or replace this pressure-release valve.

This affects the following filters: AF1633, 15601-68010, Z161X, MZ161X, WZ161X, BT221, P550707 & LF3399

See below for the official notice from the manufacturer.

“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.

In spite of these large safety margins, filter over pressurization and subsequent engine damage can and does occur; invariably as a result of a 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.

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 re-positioned at variance to its original wear track.
Valve lock up as the first sign of glycol type anti freeze build up in the oil – a result of minor head gasket leakage.
A hydraulic lock can occur with some valve designs and jam 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 the engine or oil pump is rebuilt or disassembled, 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.

An oil filter over pressurization must be seen as a symptom of an 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.”