The metal dish covering the bottom of the engine block is known as the wet and dry oil sump. It serves as a reservoir that keeps the engine oil, which circulates through the engine. This scenario applies to a wet sump.
The dry sump is located somewhere around the engine but still contains oil in the sump at the bottom. In this reading, we’ll learn what wet and dry oil sumps are, how they work, their differences, and their advantages and disadvantages.
Let’s begin!
Learn about engine lubrication systems with this detailed guide.
Wet Sump Lubrication System
The wet sump system is a common and standard oil sump in an automobile engine. We call it a wet sump because only the sump, acting as a reservoir, holds oil and utilizes a single oil pump. The oil circulating process seems to be swift in this lubricating system because the oil is pumped directly to the moving parts.
Thin-shaped stainless steel forms the sump, covering the engine underneath. It collects the oil when the engine is at rest.
Wet sumps function as oil storage/reservoirs by shaping into deeper sections and mounting them at the bottom of the crankcase. Though oil starving often occurs, there are ways to prevent it.
Functions of a Wet Sump
The wet sump serves several important purposes in a car. Here are some of its functions:
- The engine is covered 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 it enters the engine for lubrication.
- There are cooling fins in the sump, which increase its surface area.
- Oil sumps help keep big dirt out and prevent it from entering the engine. The oil filter keeps dirt small.
- The engine uses the oil it contains for lubrication, cooling, and cleaning.
- With a dipstick, the oil sump allows the oil to be a gauge.
- Oil can drain out of the oil pan or sump to allow for the installation of new oil.
Advantages
Here are the common advantages of the wet sump:
- The wet sump lubricating system is economical.
- Oil circulating is easier and faster.
- The pan/sump features some components like baffles, a windage tray, and a dipstick for oil controls.
- Wet oil sump keeps larger dirt at the bottom portion of the pan.
- This component does not add to the engine’s weight like the dry-sump system.
- Less maintenance is required.
- Commercial cars frequently use a wet sump.
Disadvantages
Despite the benefits of a wet sump system, certain limitations persist. Below are the disadvantages of a wet sump system.
- Oil circulation is limited.
- Any issues with the oil sump or pump affect the circulation of oil.
- Starving oil easily occurs in this lubricating system.
- There is only one oil pump in the system.
Learn about oil pan in this detailed guide!
Dry Sump Lubrication
IIn a dry-sump lubricating system, an additional oil reservoir exists apart from the oil pan. This system manages lubricating oil in both two-stroke and four-stroke internal combustion engines. 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, which 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.
Always place the cooler between the line of the scavenge outlets and the external reservoir. Usually, a Gilmer or High Torque Drive (HTD) timing belt and pulleys 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 removed.
Larger diesel engines, such as those in ships, typically use a dry sump system. Gasoline engines in racing cars, aerobatic aircraft, and high-performance motorcycles also use this system.
They are used on high-performance engines due to their reliability, oil capacity, less oil starvation, etc. It may not be good for all applications 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 design of the tank is tall, round, or narrow, featuring internal baffles and an oil outlet. The outlet for supplying oil is located at the very bottom, to ensure efficient oil flow.
Advantages
A dry sump system has many benefits compared to a wet sump. Below are the advantages of a dry sump system:
- It improves engine reliability due to consistent oil pressure.
- Prevent the engine from experiencing oil starvation.
- Engines with dry sump systems experience increased horsepower because of reduced viscous and air friction.
- Because of the larger external reservoir, the intake oil capacity is large.
- High-performance engines, like those in racing cars and sports cars, find enormous importance in this lubricating system.
- Oil temperature is high and perfectly controlled.
- Improve the stability and handling of vehicles.
- Pumps located externally make them easier to replace and maintain.
- A dry sump system helps control gases trapped in the oil from the engine parts.
- We improve the pump’s efficiency to maintain the engine’s oil supply.
Disadvantages
Despite the advantages of dry-sump engines over wet-sump, their limitations are still over those of wet-sump. Below are the disadvantages of a dry sump system:
- A dry sump system adds to the weight, complexity, and cost of the engine.
- Wrist pins and pistons rely on lubrication and cooling, respectively, from the polished oil. If the pump pulls away too much oil, inadequate oiling might result.
- There are extra pumps and lines in the system, which is not economical.
- The external reservoir and pumps take up a large space, leaving no breathing space or space for air to circulate externally.
- It requires additional oil and maintenance of the system.
- If too much oil vapor leaves the area, inadequate upper valvetrain lubrication may also become a problem.
Diagram Of a Wet and Dry Oil Sump
Also learn about oil pumps in this comprehensive guide!
How A Wet and Dry Oil Sump System Works
Engine oil circulates to lubricate and cool 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 transports the oil through oil galleries. The oil then returns to the sump for cooling before recirculation.
Another pump directs oil from the sump to an external reservoir in a dry sump before it reaches engine components. But the clear fact between the two systems is that the oils fall back to the reservoir at the bottom part of the engine.
Oil cooling rate differs between wet and dry sumps. Since oil in the reservoir must return to the external reservoir before recirculating, this takes time. Oil must cool in a wet sump before it can be recycled back into the engine.
The dry-sump system prevents oil shortages by lubricating the engine from top to bottom. A pressure pump cools and de-aerates engine oil before recirculating it.
Wet Sump and Dry Sump System in Motorcycle
IModern motorcycles use wet-sump lubrication because it makes sense for across-the-frame inline four-cylinder engines. Due to the fact that the engines must be mounted fairly high in the frame, the space underneath can be used for a wet sump.
Motorcycles, operating with more intense energy than other road vehicles, can benefit from dry lubrication. Motorcycles such as the Honda CB750 use a dry-sump lubricating system.
Dry-sump lubrication is a perfect feature for narrower engines, allowing for lower mounting. So, today’s focus is on understanding the differences between the wet-sump and the dry-sump lubricating systems.
Learn about crankshafts in the detailed guide!
Wet Sump vs. Dry Sump
Just as stated earlier, the 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 little power is consumed and will not likely require excess lubrication.
A high-performance vehicle requiring maximum power and control should use the dry-sump system.
Oil circulation in the wet sump is just from the sump to the engine moving parts, in case dry-sump system oil treatment (scavenged) is made in stages before recirculating. A commercial vehicle often uses the wet-sump, but racing cars use the dry-sump system.
Conclusion
Both wet and dry sump systems serve the essential role of managing engine oil, ensuring proper lubrication, cooling, and cleaning of internal engine parts.
A wet sump system stores oil in the oil pan beneath the engine and is common in most road vehicles due to its simplicity and cost-effectiveness. In contrast, a dry sump system stores oil in an external tank and uses additional pumps, offering superior lubrication under extreme conditions, ideal for high-performance and racing applications.
Understanding the differences between the two systems helps in choosing the right setup for your engine needs and maintaining optimal engine performance.
FAQs on Wet and Dry Oil Sump System
What is the main difference between a wet and dry sump system?
A wet sump system stores oil directly in the engine’s oil pan, while a dry sump system stores oil in an external reservoir and uses pumps to circulate it.
Which is better, wet sump or dry sump?
It depends on the application. Wet sump systems are simpler and more affordable for everyday vehicles, while dry sump systems offer better performance for racing and high-performance engines.
Why do race cars use a dry sump system?
Dry sump systems prevent oil starvation during hard cornering, braking, and acceleration, ensuring consistent oil pressure under extreme driving conditions.
Does a dry sump system improve engine performance?
Yes, by reducing oil drag on the crankshaft and improving engine cooling and lubrication, a dry sump system can enhance performance and engine reliability.
Is a dry sump system more expensive?
Yes, dry sump systems are more complex and costly to install and maintain compared to wet sump systems.
Can you convert a wet sump engine to a dry sump?
Yes, with the right parts and modifications, but it involves significant changes, including external pumps, tanks, and modified oiling passages.