When diesel engines operate, there is a small amount of pressure which slips by the piston rings. This pressure gets into the block and rocker arm cover of the engine and has to be relieved in some form. Typically a vent hose is attached to the rocker cover, and maybe one from the crank case. The pressurized air which is expelled carries with it a fine mist of oil. After a while everything in the engine room is covered with oil.

Another problem occurs after the engine is shut down. The hot engine pulls in cooler, damp air. The moisture in the air then condenses inside the engine and runs into the oil, mixes with the sulfur in the oil, and makes a lovely brew of acids which happily munch away on your bearings and seals. This is one of the main reasons for changing your oil.

Finally, if there are any minute oil leaks, this pressurization will make sure they seep down the engine and into the bilge.

Some years ago a company called Walker Engineering came up with a combination air cleaner and crank case vent which eliminated this problem. A filter is put in the engine’s rocker cover breather line, which is in turn connected to a special air filter. When the engine is operating, it sucks in air creating, a vacuum on the vent line. The filter precipitates the oil mist out of the pressurized air and is drained back to the bottom of the engine pan. Meanwhile, the pressurized air from the blow-by is sucked back into the engine.

These units quiet the diesel, and get rid of most of the oily mist.

Somehow Walker got crossed up with John Deere, and Deere won’t allow their units on new engines. However, Racor has something similar, so that’s what we fitted on Wind Horse.

In the photo above you can see the Racor Crank Vent air cleaner on the left side of the photo. This is where the engine gets its combustion air. Note the right angle bend between the turbo charger inlet and air cleaner. Craig Hatton suggested this as a means of quieting the engine’s air intake – it works.

That hose running out of the right hand side of the air cleaner (bottom side) goes to the blow-by filter, which is shown to the right of the photo (and below).

The breather on the rocker cover connects to the right side of this filter (that hose is not shown here). The hose coming out of the left side runs to the air intake filter. There’s a hose at the bottom which allows the precipitated oil to drain back to the engine pan. Note the clear plastic button on top. A red indicator pops up when it is time to change the filter.

Speaking of indicators, we recently picked these up from Tim Morgan at Covich Williams in Seattle (Tim also supplied our spare filters). These little devices are plumbed into the bottom of the engine air cleaners, and indicate when it is time to clean or replace the air filters.

We’d normally fit one of these systems to the genset, but the 8kW Northern Lights generator we have aboard has an air cleaner which makes this impossible. This is a real shame as the diesel itself is very dirty – we’d not use one of these again.

If you are installing a system like this you will want to get a kit which has all the various fittings and hoses for your particular engine. That will save a lot of running around. Pay particular attention to how the filter in the vent line is plumbed. There will be a minimum distance for the filter to be above the block. The drain line also needs to be above the oil level so it drains easily.

Having used these systems now for the past ten years we are sold on the concept, and would not do an engine room without a Walker AirSep or Racor Crank Vent.