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Diagnosing Filters with Collapsed Centertubes or Elements

Full flow oil filtration is a system in which all of the oil from the oil pump (that oil directed to the mating parts of the engine) must pass through the oil filter.
This means that a filter must remove engine damaging dirt and grit from the oil on the first time around. To ensure a supply of oil to lubricate the engine under all conditions, a relief valve is built into the filtering system. This filter relief valve could be located in the engine or oil filter base (attached to engine) or in the filter itself. Under normal operating conditions this valve is closed. However, this valve will open and supply oil directly to the engine whenever the filter becomes plugged with contaminants and too restrictive to oil flow. Manufacturers believe that it is better to supply unfiltered oil to the bearings than to burn out bearings by oil starvation.

Bypass or part flow systems
Bypass or part flow oil filtration systems take only a small portion (about 10%) of the oil flow from the pump. Actually, this amount is borrowed from the excess oil that would ordinarily be returned to the engine oil pan or inlet side of the pump through a passage-way controlled by the
engine pressure regulation valve.
Oil flow through a bypass filter is regulated by the use of a metering orifice within the filter. Oil which has been filtered is returned to the engine oil pan directly and not to the mating parts of the engine as with the full flow system.

Over-Pressurized lube oil filters
From time to time every filter manufacturer has a filter that has been severely over-pressurized returned from a customer. Often the deformed filter is the only sign the car owner has that a problem existed in his lube oil system. It's possible that the damaged filter was not noticed until it was removed during the next scheduled oil change. However, if the pressure was sufficient to blow out the gasket or unroll the lockseam, the car owner may have experienced immediate and costly problems.
With the "evidence" in his hands, he tends to put the blame on the damaged filter. It's not surprising that his more than a little aggravated when the filter manufacturer denies any responsibility for the damage .
What, then, has caused the over-pressurization?
A look at how a lube oil system functions will show that oil pressure is created by the oil pump.

The upper limit of this pressure is controlled by a pressure regulating valve which is usually an integral part of the pump. Figure 1 is a simplified diagram of the lube oil system showing the pump, regulating valve, filter and bearings
The pump supplies sufficient flow to lubricate the bearings and other moving parts of the engine. This oil must be under pressure if it is to properly separate the highly loaded parts of an engine and prevent excessive wear. The purpose of the regulating valve is to provide this pressure which on most passenger cars is between 40 and 60 PSI.
The regulating valve is made up of a ball or plunger which regulates pressure with aid of a spring. The spring is calibrated so that the plunger will lift off its seat when the oil pressure reaches the desired amount. Once the valve is open, the pressure remains fairly constant with only small changes occurring as the engine speed varies.

The filter and all other components in the system are subjected to the pressure established by the regulating valve. If this pressure is excessive, filter damage may occur. This is the point that many people who are not familiar with lube systems fail to realize. What can cause the pressure in the system to exceed the regulating valve setting? The answer is that either the valve must be stuck in the closed position or it is sluggish and slow to move to the open position after the engine has started.
Figure 2 shows the system operating with the regulating valve stuck in the shut position. Under these conditions the pressure builds up equally on all components in the system until something happens to relieve the pressure. If the regulating valve becomes unstuck, the pressure will return to normal. If it remains stuck, something has to break. Normal operating pressure caused no permanent deformation of the filter body. When the system pressure reaches 150 PSI due to a faulty regulating valve, most filters become permanently deformed. At this pressure the gasket usually will not blow out and the lockseam will remain sound.

If the regulating valve still remains stuck, the pressure will increase further and the gasket between the filter and the base can be blown out. This will probably cause the loss of all the oil in the system.
If the filter has been installed on the tight side, the gasket may not blow out and the lockseam will unwind as the pressure continues to rise.
If the customer is alert and shuts the engine off at the first sign of trouble (red light on or reduced oil pressure) he can limit his loss to a tow job, oil change and new filter. If he drives to the nearest garage, he will probably burn up the engine due to lack of oil. The main point is that the deformed filter is not the cause of this excessive pressure, but is the victim of a faulty regulating valve.
The customer may ask if a filter that is completely plugged could have caused the over-pressure conditions in the system.
The answer is no. If the regulating valve is functioning properly it will maintain the pressure on the filter at 40 or 60 PSI even if filter is plugged.
In summary, if a filter distorts due to overpressure in the system, the fault lies with the regulating valve and not with the filter.