Table of contents: Low oil level ↓ Clogged oil filter ↓ Liquid or diluted oil ↓ The oil pump pressure relief valve…↓ Damaged oil pump oil pickup tube ↓
Low oil pressure can be caused by several reasons that do not require engine repair. These include the following: low oil level; the oil filter is clogged; liquid or diluted oil; the oil pump pressure relief valve is stuck open; the oil pump oil intake tube is damaged.
Low oil level
Checking the oil level is necessary before deciding to repair the engine. When the oil level is low, the oil pump's oil pickup tube has difficulty drawing in enough oil to maintain the proper pressure in the engine's lubrication system. Low oil pressure under these conditions is a small matter compared to the damage that can cause low oil pressure. Probably the best preventative measure in this case is to check the engine oil level at least once a week and add oil as needed.
Clogged oil filter
The simplest or most obvious reason for low oil pressure is a clogged oil filter. Unfortunately, it is not possible to say for sure that this is usually the result of carelessness or errors. If the oil has not been changed during the time the engine suffered from low oil pressure, the oil and filter should be replaced.
Liquid or diluted oil
The idea of buying oil that is too thin (i.e. with low viscosity), pretty stupid. If you are using oil that was purchased for the purpose of lubricating a car engine, it is almost impossible to purchase oil that will itself cause low oil pressure. Some people may disagree with the statement that using thick, high viscosity oil will cause high oil pressure. This is often true. However, if the engine's lubrication system, oil pump and bearings are in good condition, even low-viscosity oil will be able to provide the required oil pressure.
Diluted oil is a different matter. Oil becomes diluted in several ways. Perhaps the most common method is the one described below. When the engine is running, especially after starting, some of the exhaust gases escape past the piston rings and enter the engine crankcase. These gases contain some amount of unburned fuel. Unburned fuel dilutes the engine oil. This dissolved oil can cause low oil pressure. But an even more critical phenomenon can occur, which is that unburned fuel, combined with moisture in the crankcase, can form an acid that can damage bearings and their surfaces for quite a long time before the low oil pressure caused by its dilution can damage the engine.
Another way is that the engine oil can become diluted by the coolant. If the cylinder head gasket begins to leak, or if the cylinder head or block cracks, coolant can leak into the combustion chamber and/or crankcase and dilute the engine oil.
While low oil pressure due to engine oil dilution can be diagnosed with a simple oil change, the question remains: does the engine require a major overhaul due to a problem caused by diluted oil? Another question is: how much damage has resulted from diluted oil? A simple oil change may increase oil pressure, but the engine may already be damaged, and this damage must be addressed before catastrophic consequences occur.
The oil pump pressure relief valve is stuck open
The engine is equipped with an oil pressure reducing valve in the oil pump. The valve's purpose is to limit the oil pressure to a level that prevents the oil filter from turning into a shrapnel grenade. Occasionally the relief valve will stick open, allowing oil to be pumped by the oil pump and returned back to the oil sump. This fault is very difficult to diagnose and may require a complete engine overhaul.
If time is not a critical parameter, remove the oil pump and replace it with a new one. While it is possible to repair a pressure relief valve, there is little point in doing the repair "just in case.".
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Damaged oil pump oil pickup tube
When the oil pump is removed during the installation of a new pump, inspect the feed pipe for possible damage. If the tube is cracked or loose, the oil pump will not be able to suck oil from the oil pan. This will cause low oil pressure. Before replacing the oil pump, make sure the feed pipe is in good condition.