74 240D Oil Bath Air Filter Service

My 1974 240D 115 has an oil bath filter. What type of maintenance does this type filter require?

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Chassis Model Number

W115

Cleaning and Servicing Procedure

Air Cleaner Service Instructions for the 115 chassis 220D and 240D 1968 to 1976.

The element inside the air filter housing is cleanable and does not need replacement unless it is damaged. This is called an oil bath filter because the filter element sits in a small bath of engine oil at the bottom of the filter housing. Oil is mixed with the incoming air to "grab" fine dirt particles and the mesh screen removes the oil and dirt from the air before leaving the filter and entering the intake manifold. I know it is a little messy but has proven to be a very effective filtering device. Other industrial diesel engines have used this type for years. Just look at how dirty the oil gets at the bottom of the housing and you will see how effective it is. If you have diesel engine blow-by this style filter is works better because the oil would plug a paper filter - but in this case it just adds to the filtering mesh without restriction.

To service, remove the filter element from the housing and place in a bucket filled with diesel fuel. Let it sit in the diesel for an hour or two while shaking it from time to time. Remove from the bucket and let drain. When reasonably dry pour engine oil through the mesh to coat all surfaces. Clean (wipe) the old oil out of the bottom of the housing. Note the fill mark near the bottom. Pour engine oil into the housing until it reaches the mark. Replace the element and the lid and you are ready to go for another 15,000 to 25,000 miles (depending on driving conditions). Pull the lid and inspect the level at every oil change. Add oil if required but DO NOT overfill.