OIL PRESSURE: FINDING THE RIGHT BALANCE TO RUN YOUR ENGINE

Total explains how the right balance impacts the operation of your vehicle and how you can correct it.

Life is a question of balance. It might seem like hot air, but the truth is we can find hundreds of examples in nature, chemistry and physics. The concept we are going to explain today has a lot to do with physics and balance. That concept is engine oil pressure, which should be maintained at the correct level so that the vehicle can function perfectly.

You may well be wondering what oil pressure is. The first thing you need to know is that it involves several main elements: the oil pump, the lubricant and the distance that it travels to reach the vehicle’s various parts.

Oil pressure is a measure of the force pushing the lubricant through the oil pump, as well as the distances it must cover, i.e. the meters of pipes, joints and filters it must pass through, among other parts, which reduce this force. Thus, if we measure the pressure in the pump, we will get a higher result than in another part of the circuit.

What causes oil pressure to change?

When you start the engine, the pressure will be high, as the oil is cold and the pump will need more power to move it. Once the engine has started, the lubricant is heated and flows much easier, thereby reducing the pressure shown on the pump’s pressure gauge.

This is one of the reasons why there are multi-grade oils, which are more fluid than single grade oils upon starting and therefore prevent wear in that phase, as they ensure, from the outset, that a sufficient amount of oil is provided to separate the metal parts and to avoid friction between them.

What does high pressure mean?

The way the oil pump works basically consists in sucking the lubricant through a mesh, which blocks larger pieces of dirt, and channeling it down to the lubrication system. The pumps are often spur gears that are lubricated by the passing fluid and have a valve to remove oil when the pressure is too high. You must also bear in mind that these are constant flow pumps.

High pressure in the pump usually implies that there is unusual resistance in the system that must be overcome, such as dirt caused by dust or carbon deposits, which is blocking the oil flow. This means that the pump has to operate at a higher power.

This risk of high pressure also occurs in the coolers and filters in the event of obstruction, which is why they also feature safety (by-pass) valves set at a certain pressure. The risk of blockages in these systems is high and is something that is of great concern to vehicle manufacturers.

In order to avoid these risks, it is necessary to find an adequate design for the tubes and the various lubrication points. It is also essential to use a lubricant whose viscosity is suited to the engine. This is the best way to keep the oil pressure at the right level.

Remember that if the tubes are narrow and the oil is too viscous, meaning it doesn't flow as well, the pressure in the system will need to be increased in order to move the oil. As for the viscosity, if it is too fluid, the pressure will drop, which will have the same effect as if the tubes were changed for larger ones.

This is why we say that the pressure of the system depends on the characteristics of the oil (viscosity) and the manufacturer’s design, for example the pump, pipe diameter and length.

How can I correct inadequate oil pressure?

A vehicle’s actions and symptoms can be the result of different causes, for which there are various solutions. If you run a garage, the following tables will be of great use to you.

Low oil pressure

	Effect	What to do
Change in oil or oil brand.	If it is the same type of oil (SAE and standards), you should not see any effect.	If the pressure varies, check the pressure gauge and see if there is anything clogging the system. The engine may need to be cleaned.
	If the oil does not have the same characteristics, it may result in increased consumption and wear.	A more synthetic or detergent oil, or a different SAE oil can result in an increase or a drop in pressure depending on its characteristics.
Low oil level in the crankcase.	The pump can’t suck much oil.	Add oil, see why the level has dropped (leak in the crankcase, broken crankcase, etc.).
Oil that doesn’t flow at low temperatures.	The pump cannot move the oil in the starter.	Use a more fluid oil in the starter, usually synthetic.
Worn oil pump.	Lubrication problems, loss of power in the pump.	Have the pump serviced or replaced; check pump gears.
Worn bearings.	Lubrication problems, loss of power in the pump.	Change the bearings.
Fuel contamination.	Loss in viscosity, wear.	Change the oil and have the injection system serviced.
Change from a mineral oil to a synthetic oil.	Increase in oil consumption.	The synthetic oil cleans the dirt accumulated in an old engine, which increases the oil flow, decreases the pressure and increases the amount of oil that reaches the combustion chamber, increasing the consumption of lubricant.
Engine overheating.	Fault in engine cooling.	Decrease in oil viscosity due to the temperature; when the engine cools down, its returns to the initial pressure.

High oil pressure

	Consequences	What to do
The pressure stays high from the moment the car starts.	Lubrication fault.	The viscosity may be too high due to high carbon deposits; change the oil and clean the engine; check the turbo filter
The pressure stays high.	Lubrication fault.	It's possible that the oil may be oxidized causing an increase in viscosity; change the oil.
Blocked filter.	Dirty oil passes through the system.	Change the oil and the filter.
Deposits in the lubrication tubes.	Lubrication fault due to lack of oil.	Change the oil and the filter; clean the engine; check the turbo filter.
The viscosity of the lubricant is inadequate.	Lack of oil in the system.	Check the appropriate SAE in the maintenance manual.

To recap

Remember that the pressure indicated on the gauge is designed to show the effort required by the pump to move the oil, creating the flow required by the system to provide the correct lubrication. The pressure indicated on the pump gauge has nothing to do with the pressure between the parts of the system, such as the crankshaft bearings or cams, which is different.

Bear in mind that this gauge must indicate a level between the minimum and the maximum; this shows that the lubrication process is occurring correctly. If it is above the maximum or below the minimum level, it’s not a good sign.

You must also remember that these levels may vary according to the manufacturer’s design, which ensures that the vehicle operates between a set minimum and maximum pressure, controlled by the pump, to obtain proper lubrication.

If the vehicle exceeds the maximum level, the gauge will tell you that the lubrication is inadequate (pump problems, oil too viscous or blockage in the system). As the energy used by the pump comes from combustion, this will result in higher fuel consumption.

If the pressure is below the minimum level on the pressure gauge, it may be that the oil is too fluid, either because the SAE is too low or because there is fuel in the oil. It may also be due to an oil leak in the system, which reduces its resistance to flow. Taking a sample of oil can help detect possible contamination and determine why the pressure is not correct.

As you can see, choosing a high-quality oil that is suited to the engine of your vehicle is very important for maintaining the balance in the engine and ensuring that it can work in an optimum manner. Don’t forget to always use lubricants that meet the engine’s requirements.