Lubrication 12 - Dry Sump
|Two-stroke motorcycles nearly always have a dry-sump lubrication|
|More and more four-wheel vehicles with a dry-sump lubrication|
As far as four-wheeled vehicles were concerned, in contrast to their two-wheeled counterparts, a dry-sump lubrication was reserved for quite fast sports- or racing cars and for cars being driven on extreme off-road
surfaces. Nowadays, it can also be found in top-of-the-range luxury cars and in the more noble all-wheel-drive models. Apparently there are a number of good reasons why the added effort is being accepted.
|Additional oil-tank instead of an oil pan|
Instead of having only one oil-pump to do the job, there are now two or even more. The additional pumps continuously try to empty the generally much smaller oil pan, of course, they never suceed completely. They
transport the engine-oil into a special tank. The other pumps also supply - as always - the various lubrication points in the engine from this tank. There is always sufficient oil available, a brief running dry, is practically
impossible. Thus, the dry-sump lubrication always needs at least one additional pump (the lower one in the picture) and a tank for the pressure-
circulation lubrication. 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.
|Better for cornering, off-road and for the center of gravity|
This construction becomes necessary, when driving conditions occur, which prevent the oil from being continuously being sucked out from the oil pan. This happens, e.g., at extreme cornering speeds or when the
vehicle leans over at great angles. There are however, also other reasons. One can thus, increase the oil-reservoir almost at will, one reason why standard vehicles with a dry-sump lubrication mostly have a greater oil-
change volume. Apart from which, the oil-tank can be placed in an area where more cooling is available, (e.g., in the wheel housing), which is particularly important nowadays because the undersides of the cars are
closed in almost completely.
|A lower center of gravity and better aerodynamics are possible …|
Due to the very shallow oil pan, the engine can be installed lower down, thus lowering the center of gravity as well. This can also be significant for the aerodynamics, eg., when the bonnet is curved downwards in the
front, almost like a spoiler. Indeed, the construction size of the clutch must then also be considered. In racing cars, the fact that the oil-tank is far away from the engine, also allows the center of gravity to be horizontally
|Distinctly longer warm-up phase must be taken into consideration ...|
Indeed, apart from the higher costs, there are also other disadvantages, not so much for the racing cars, but for standard vehicles. Because the increased amount of oil requires more time to reach the operating
temperature. If the oil-amount were, e.g.,25 liters (quite possible in racing cars), one would have to calculate, even with these very hot engines, a good 20 minutes of warm-up time.
|Too much oil cooling is possible ...|
Even though a standard vehicle can manage with a great deal less oil, one should not, if possible, use the vehicle for very short distances. If the engine has been so highly modified, that it needs an oil-cooler, then the
oil-tank should definitely not be placed in the airstream. Since, if the performance potential of the engine is not exploited, the oil can be too strongly cooled. This can be remedied by having an additional, thermostatically
The question of the oil-level can also cause difficulties. If there is not an electronic oil-level control, like e.g., in the current Porsche, then reading up in the users manual won't do any harm at all. There you may find, that
the engine should be warmed up, before the oil-level can be determined. Apparently, in these vehicles, the dry-sump lubrication oil-tank contains varying amounts of oil, depending on whether the engine is cold or hot.