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Understanding Wet and Dry Oil Sump System

Do you really have basic knowledge on the engine lubrication system, if so, you are familiar with a term oil sump? The basic types are the wet and dry sump which is your purpose here today.

The part is a metal dish that covers the bottom of the engine block. It serves as a reservoir that keeps the engine oil, which from its oil circulate around the engine. That is the case of a wet sump. The dry sump is located somewhere around the engine but it still contains oil in the sump at the bottom of the engine.

dry and wet lubricating system

In this article, you will get familiar with the working of the wet and dry oil sump, as well as their differences and advantages and disadvantages.

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Wet Sump Lubrication System

The wet sump system is common and standard oil sump in an automobile engine. it’s called wet-sump because it contains oil in just the sump, serving as a reservoir and it uses a single oil pump. Oil circulating process seems to fast in this lubricating system because the oil is pumped from directly to the moving parts.

The sump is made of thin shaped stainless metal which is used to cover the engine beneath. It collects the oil when the engine is at rest. Wet sumps are shaped into deeper section and it’s mounted at the bottom of the crankcase serving as oil storage/reservoir. Though oil staving often occurs there are ways to prevent it.

The following are the purposes of a wet sump, which is why its vastly used in automobile engines:

  • The engine is cover completely, preventing external dirt from entering.
  • Oil sumps also help in the cooling of lubricating hot oil as the vehicle moves. There is airflow under the sump, which helps to cool the hot oil before entering the engine for lubrication.
  • There are cooling fins in the sump which increase its surface area.
  • Oil sumps help to keep big dirt and prevent them from entering the engine. small dirt is kept by the oil filter.
  • The oil it contains is used for lubrication, cooling, and cleaning of the engine.
  • With a dipstick, oil sump allows the oil to be a gauge.
  • Oil pan/sump allows oil to drain out so new oil can be installed.

diagram of a wet sump system

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Advantages and Disadvantages of Wet Sump System

Advantages:

Below are the benefits of a wet sump system:

  • Working is not complex, that is, it is easy to understand the oil circulation.
  • Wet sump lubricating system is economical.
  • Oil circulating is easier and faster.
  • The pan/sump features some components like baffles, windage tray, dipstick for oil controls.
  • Wet oil sump keeps larger dirt at the down portion of the pan.
  • This component does not add to the engine’s weight like the dry-sump system.
  • Less maintenance is required.
  • A wet sump is widely used for commercial cars.

Disadvantages:

Despite the advantages of a wet sump system some limitation still occurs. Below are the disadvantages of wet sump system.

  • Oil circulation is limited.
  • Any issues with the oil sump or pump affect the circulation of oil.
  • Starving of oil easily occur in this lubricating system.
  • There is only one oil pump in the system.

Watch the video to have more understanding of how wet-sump lubrication work:

Dry Sump Lubrication

In a dry-sump lubricating system, there is an extra oil reservoir aside from the oil pan. It’s a process to manage lubricating oil in both two-stroke and four-stroke internal combustion engine. Oil is pumped at different stages in the system, at a minimum of two, with as many as 5 or 6.

The first stage is for pressure supply, which supplies oil from the bottom of the reservoir, along with an adjustable pressure regulator, it supplies oil under pressure through the filter into the engine. The next stage is scavenging the oil out of the dry-sump pan and returning the oil and gases to the external reservoir.

Cooler is always used between the inline of the scavenge outlets and the external reservoir. A Gilmer or High Torque Drive (HTD) timing belt and pulleys are usually used to drive the pump. The reason for the several stages is to ensure all oil is scavenged from the pan and also to ensure excess air from the crankcase is remove.

Dry sump system is mostly used on larger diesel engines like the ones used in ships. It is also used on gasoline engines used in racing cars, aerobatic aircraft as well as high-performance motorcycles. They are used on high-performance engines due to their reliability, oil capacity, less oil starvation, etc. it may not be good for all application due to its high cost, complexity, etc.

The primary purpose of this system is to have a separate tank or reservoir to store oil. The tank is designed to be tall and round or narrow and contained internal baffles and an oil outlet. The outlet for supplying oil is located at the very bottom not to hinder oil supply.

diagram of a dry sump system

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Advantages and disadvantages of a dry-sump system

Advantages:

Dry sump system has many benefits compared to the wet sump. Below are advantages of a dry sump system:

  • It improves engine reliability due to consistent oil pressure.
  • Prevent engine from experiencing oil starvation.
  • Engines with dry sump system experience increased in horsepower because of reduced viscous and air friction.
  • Because of the larger external reservoir, intake oil capacity is much.
  • High-performance engine like racing cars, sports cars find great important with this lubricating system.
  • Oil temperature is high and perfectly controlled.
  • Improve the stability and handling of vehicles.
  • Pumps located externally makes them easier to replace and maintain.
  • Dry sump system helps to control gasses trapped from in the oil from the engine parts.
  • Pump efficiency is improved to maintain oil supply to the engine.

Disadvantages:

Despite the advantages of dry sump engines over the wet-sump, its limitations are still over that of the wet sump. Below are the disadvantages of a dry sump system:

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  • Dry sump system adds to weight, complexity and cost of the engine.
  • As wrist pins and pistons depend on lubrication and cooling respectively on the plashed oil. Inadequate oiling might occur if too much oil is pulled away by the pump.
  • There are extra pumps and lines in the system, which makes it not economical.
  • The external reservoir and pumps take large space leaving no breathing spacing or space for air to circulate externally.
  • It requires additional oil and maintenance of the system.
  • Inadequate upper valvetrain lubrication can also become an issue if too much oil vapour is being removed from the area.

Watch the video to have more understanding of how dry sump lubricating system work:

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Working principle

Purpose of oil in engines is to lubricate and cool its parts through circulation, oiling various bearings and other moving parts. The oil is then drained through gravity into the sump at the base of the engine. in a wet-sump system, a pump collects the oil and transfer to their destination through the oil galleries. The oil then returns to the sump for cooling before recirculation.

In a dry-sump, oil is pumped from the sump to the external reservoir before another pump pushes the oil to the engine parts. But the clear fact between the two systems is that the oils fall back to the reservoir at the bottom part of the engine.

One of the differences between the wet and dry sump will be the oil cooling rate. This is because it will take time for the oil in the reservoir to return to the external reservoir before recirculating. However, in the case of wet-sump, no alternative to giving enough time for the oil to properly cool before it recirculates to the engine.

There will not be oil starvation in the dry-sump system because the lubrication starts from the top portion of the engine to the bottom parts. Oil is properly cooled and de-aerated before being recirculated through the engine by a pressure pump.

Wet Sump and Dry Sump System in Motorcycle

In modern motorcycles, wet-sump lubrication is used because it is understandable across-the-frame inline four-cylinder engines. Due to the fact that the engines must be mounted fairly high in the frame, which is why space under can be used for a wet-sump.

Dry-lubrication is applicable to motorcycles as it is operated with more intense energy than other road vehicles. Motorcycles such as the Honda CB750 uses a dry-sump lubricating system. Narrower engines can be mounted lower and can perfectly feature dry-sump lubrication.

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So, the big question today is the difference between the wet sump and the dry-sump lubricating system is.

Wet Sump vs Dry Sump

Just as earlier stated, wet-sump stores oil in the oil pan while the dry-sump system has an external reservoir for oil storage. So, the big difference between the two is that wet sumps are used on small engines where small power is consumed and will not likely need excess lubrication. Whilst the dry-sump system is meant for a high-performance vehicle where maximum power and control are required.

Oil circulation in the wet sump is just from the sump to the engine moving parts, in case if dry-sump system oil treatment (scavenged) are made in stages before recirculating. A commercial vehicle often uses the wet-sump, but racing cars uses the dry-sump system.

In conclusion, wet-sump engines are designed with one oil pump. It is located below the crankshaft of the engine and it supplies oil from the sump directly to the engine. whilst the dry-sump engine has external oil storage aside from the sump and it’s designed with multiple oil pumps.

The difference between wet and dry-sump system is their applications. Just as stated, a wet sump is found on commercial vehicles while the dry-sump is used on high-performance engines such as sports cars.

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That’s it for this article “oil sump system”. I hope you enjoyed the reading, if so, kindly comment, share and recommend this site to other technical students!

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