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Here we are going to look at tractor oil bath air filters. How they work, what oil to use and the maintenance of the oil bath filter in your tracor.

How They Work

The general principal of an oil bath air cleaner is that incoming air is sucked downwards through the system towards a bowl containing a reservoir of oil. Figure 1 shows how the airflow has to make an abrupt change in direction from travelling downwards towards the oil pool before then heading back upwards to the filter outlet. The air changes direction easily, however any dirt carried in the air is unable to make the turn due to its inertia so it continues straight on into the oil where it is trapped. This system is considered satisfactory for engines which are generally working in clean air environments such as carsoil-bath-air-cleanerTractor engines work in dusty conditions and so the majority of manufacturers have progressed this principle to make it even more efficient at capturing the last remaining particles of dirt. The bottom of the air inlet pipe is submursed below the oil level so that the air must pass through the oil (Figure 2). At this stage the larger particles are captured by a combination of the inertia principle as detailed above and by centrifugal force created within the oil reservoir. As the air heads back upwards under suction through the filter it now must pass through a packing material (fibre, mesh, foam or metal shavings). The air carries with it some oil up into the packing material where smaller dust particles become trapped and the cleaned air continues upwards and out of the air cleaner. The process of the air carrying oil with it up into the packing material has the effect of washing the dirt particles back down into the reservoir.

complex-oil-bath-air-filterOil bath air cleaners have been largely replaced by dry paper filters in most modern tractors, as the oil makes servicing both messy and inconvenient due to the frequency of cleaning required. Oil bath filters are, however, very efficient at capturing dirt and can sequest a large amount of dirt relative to their size, without loss of efficiency. They are probably more efficient at providing clean air to your engine than modern paper filters.

Servicing and Troubleshooting

Dirty oil will not be able to wash the particles down from the packing material. The reservoir should be cleaned and filled with new oil each day or twice daily in dusty conditions. Be sure to remove all the sludge from the bottom of the reservoir.

Use the correct grade (weight) of oil. If the oil is too heavy it will not be carried up by the air onto the packing material. Conversely, if the oil is either too light or the reservoir is too full then oil can be carried through the packing material and towards the engine. In petrol fuelled models this can enrich the fuel mixture in the carburettor and not only increase exhaust emissions of unburned hydrocarbons but also increase fuel consumption. Inspect the inside of the clean pipe for any traces of oil. If you cannot find the specification for the oil then as a general rule your system will usually be designed to use the same type of oil as the lubricating oil in the engine. In very cold conditions it may be necessary to use a lighter oil or dilute the oil with up to 25% paraffin to manipulate the oil viscosity.

Hoses must be in good condition as the filter on your tractor will be engineered for the air volume and velocity created by your engine; cracked hoses will create differences in operating pressures.


The Vintage Tractor Engineer says:

March 25th, 2008 at 5:19 am
The design of the air filter is slightly different for the petrol engine compared with the diesel engine. However, the principal is the same and they both just rely on the use of the wire mesh and the oil.

MF recommend that the air cleaner should be cleaned every 8 hours (or even twice a day in dusty contitions) – it will also help if the tractor has the air intake protruding above the bonet.

I do not know many people who clean their air filter every 8 hours, but doing so will prolong the life of the engine. The oil should be changed, using the same grade as the engine oil. In very cold weather it is permissible to add up to 25% paraffin so that the oil flows freely.

Hopefully your wire mesh should be in sound condition. If so, you can clean the entire unit occasionally using paraffin. Afterwards, the element should be thoroughly dried out with an air jet.

The petrol engines tend to be fitted with one wire mesh which is in the main body of the filter. The diesel engines tend to be fitted with one wire mesh in the main body of the filter and another detachable one in the lower
(removable bowl) part of the filter, just above the oil reservoir.

Hope that gives you some useful information.

Bob McCurry says:

June 17th, 2008 at 2:58 pm
where can I get a gasket for my JD 710 ag tractor’s oil bath air filter? No parts are available in the US or Canada. this is a tractor made in Germany, sold in Europe and Canada.

The Vintage Tractor Engineer says:

June 17th, 2008 at 7:08 pm
Hi Bob,

John Deere have an online parts search website…


….Otherwise, I guess your best option may be to try a JD dealer in the UK
such as RBM…..


….they may be able to find the part for you and ship it over.

Hope you are able to source the part.