Dry Sump Lubrication

Before we talk about 4-wheel vehicles, a word about the two-wheelers. Some time ago, the more powerful motorcycles started being powered almost exclusively by 4-stroke instead of by two-stroke engines, the dry-sump oiling system is especially frequent here. An indication of this is that the construction of 'chopper' motorcycles can even be seen on television nowadays. Not really machines which have to satisfy particularly high cornering demands. Nevertheless, one of the first questions asked, e.g., by the people at OCC (Orange County Choppers) is: "Where to put the oil tank?"

The dry-sump oiling system for 4-wheeled vehicles was, for a long time, reserved for fast sports cars, racing cars and extreme off-road vehicles. The dry-sump system can now also be found in luxury-super class cars and in noble all-wheel-drive vehicles. There are obviously many reasons to accept the extravagance of the system.

Instead of one oil pump there are now two or more at work. All exept one of them repeatedly empties the often considerably smaller oil pan and pumps the engine oil into a special container. It is from this container that the last remaining pump, as before, supplies oil to the various lubrication points of the engine. There is always enough oil available, also brief dry running is practically impossible. A dry-sump oiling system necessitates at least one second pump (in the picture below) and a connection to the pressure circulation lubrication.

This construction becomes necessary during driving conditions where the oil cannot, with reliability, be taken continuously from the oil pan. This can occur e.g., during extremely high cornering speeds or when driving on steeply sloping terrain. There are also other reasons. The oil reservoir can be increased almost arbitrarily, one of the reasons why standard vehicles with dry-sump oiling systems almost always have a larger amount of oil to change. Moreover, the oil container can be placed in areas of greater cooling (e.g., in the wheel-housing), especially important nowadays where the underside of the vehicle is almost sealed. Also, due to the smaller oil pan the engine can be mounted lower which means a lower center of gravity. In this case however, the overall size of the clutch is also a fact to be considered. The center of gravity in racing cars can even be horizontally shifted because of the distance from the engine of the oil container. 06/08