Oil bath air filter

An oil bath air filter is a component on older motor vehicles . It is an air filter that does not work with a paper filter insert , which is common today , but instead directs the air flow sucked in by the engine in front of the carburetor or the injection system to filter particles through a small, separated amount of mineral oil , usually oil of the same type circulates in the motor. Oil bath air filters were used on passenger cars up to the mid-1970s, but are still used in some cases in commercial vehicles and construction machinery today.

Oil mesh filter

There is another type of filter, which is seldom or mainly used in two-wheelers , in which a metal mesh is immersed in oil and the purpose of the wetting is to (partially) adhere solid particles to the oil-soaked mesh. Strictly speaking, however, this design is not an oil bath air filter, but a line filter with an adhesive effect.

These nets disadvantageously leave harmful free cross-sections between the oil-wetted meshes, through which particle-laden air can flow without the particles being captured. As a result of this filter design, the wear effect of this only partially filtered intake air is higher than with a flat oil bath through which the intake air must flow completely.

Maintenance requirement

An oil bath air filter does not wear out as a filter (in contrast to a paper filter insert), but it gradually loses its permeability over time due to clogging of the oil with solid particles and soil sludge formation. At some point, the suction resistance increases so much due to sludge deposits that the air ratio lambda becomes too small.

Therefore, fixed oil change intervals are usually given, e.g. B. with the VW Beetles 5000 km or with the BMW R26 motorcycles 2500 km. When changing the oil, it is not only necessary to wash off or dispose of the oil, but also to remove the layer of sludge from the flat bottom of the filter.

maintenance

An oil bath air filter is usually shared for cleaning and changing the oil filling. First, the air intake line is separated at elastic connections, usually with the help of screwed hose clamps .

Then the upper part together with the metal net is usually separated by several clips, removed from the lower part and washed out in a cleaning liquid, e.g. B. Diesel oil. The oil is poured off in the lower part, then the mud is cleaned off and the entire lower part wiped dry. Then the lower part is refilled with the specified amount of fresh oil and the upper part is put on. After connecting the air intake line with hose clamps, the oil bath air filter is ready for operation again for a few 1000 kilometers.

The filling amount of oil and the sludge added from the filtered particles are therefore substances that are subject to disposal . Due to increasingly difficult handling and disposal problems, vehicle manufacturers switched to paper filters (initially called "Micronic filters") in the 1970s.

For vehicles that have to be operated in environments with a high proportion of foreign matter (e.g. dust), oil bath air filters are increasingly being replaced by a combination of cyclone filters for pre-separation and paper air filters.

source

R. v. Basshuyen, F. Schäfer: Lexikon der Motorentechnik , Vieweg-Verlag, Wiesbaden 2004, ISBN 3-528-03903-5