Oil Pressure Relief and Flow
The oil pressure in an engine is effected by different factors. The oil pump creates oil pressure and sends the oil to the oil filter. There is more to the typical oil filter than meets the eye. Inside the average filter is the inlet check valve and the bypass valve. The inlet check valve prevents oil from draining back from the pump when the engine isn't running. The bypass valve is used in case the filter gets clogged. The valve opens and allows the oil to bypass the oil filter and run straight through the engine. Oil flows from the outside of the oil filter through the filter element and then through the middle before re-entering the engine.
An oil pressure relief valve prevents excessive oil pressure from developing in the engine. The oil relief valve usually contains a spring that allows just enough oil to bypass the system and return to the sump or oil pan. If the valve is stuck closed engine oil pressures would rise. This could result in high oil pressure and a ballooned oil filter. On the other hand, if the oil pressure relief valve is stuck open the oil pressure will be too low possibly resulting in engine damage.
Be careful when removing an oil pressure relief valve, note the direction of the valve in the pump housing or block and visually inspect the valve for scoring. Installing the valve in backwards may result in no pressure at all. Use an oil pressure gauge to read and diagnose any oil pressure problems.
Contaminated oil could clog the oil filter and result in catastrophe. As mentioned earlier the oil filter bypass valve opens to prevent engine damage in case the filter gets clogged. If the valve were to remain closed in the clogged filter serious engine damage may occur. A stuck open oil bypass valve would allow the oil to bypass the filter and flow through the system.
