A dry sump is a lubricating oil management system which is commonly used in four stroke and big two stroke engines. It uses an external reservoir to store the oil and an external pump to circulate it. In four stroke engines, both lubrication and cooling is done by the lubricant oil.
Like the wet sump system, the lubricant still falls at the base of the crank case. But unlike the wet sump system, it falls to a much deeper collection area. From there it is taken to a reservoir which is outside the engine and is cooled and deaerated. The oil pumps that perform this are called the scavenge pumps and are also located outside the engine and they are run by a belt that is connected to the crankshaft. The pumps which draw the oil from the reservoir and send it back to the engine with pressure is called the pressure pump. Both of these pressure pumps are connected to and are run by the crankshaft. Due to their design, one pulley at the front can run a certain number of pumps according to the need of the engine.
Advantages of the dry sump system
- The obvious advantage of a dry sump system is the increased oil capacity is offered by the reservoir which is kept away from the engine.
- Since the reservoir is located in a different place and due to the thinner size of the sump, the engine can be mounted low in the vehicle. This provides better center of gravity.
- Since the reservoir is external to the engine, it can also be used to improve weight distribution in the vehicle by relocating it to different positions.
- Since more oil can be added due to the bigger size of the reservoir, it helps in better cooling of the engine and along with the transfer of oil, the blow-by gases also gets released.
- Another important advantage is the issue of oil movement. In splash and pressure wet sump systems, due to cornering forces, the oil in the sump is displaced to a corner and the pickup tube would be uncovered temporarily. This problem is easily overcome in dry sump engines as the pickup pumps receive oil from the engine not by pressure but by gravity.
- In a wet sump, excess of oil around the crank shaft can get on it and decrease horsepower. Studies show that there is increase in working efficiency as much as 15 hp by changing to a dry sump.
- Easy to repair as it does not require opening up the engine.
- The cost is much higher compared to that of a wet sump, and is more complicated.
- Since a separate tank is needed, extra space has to be managed for this purpose.
- The pump requires its own drive belt, which makes it difficult to accommodate in front wheel drive vehicles.
- The pump should be placed very low for good scavenging and this again takes up space which can be used by other components.