BENDIX TCH-001-032 User Manual

Technical Bulletin

Bulletin No: PRO-01-32 Effective Date: 2/1/98 Cancels: PRO-01-32 dated 8/1/88 Page: 1 of 3

Subject:

TROUBLESHOOTING COMPRESSOR OIL PASSING

GENERAL COMMENTS

Some oil carryover from the air compressor into the air brake system occurs as a normal part of all air compressor
operation. It is typical to find some presence of oil at the inlet and discharge ports of the air. Oil present at the
exhaust of drain valves, air dryers or aftercoolers is normal and indicative these components are functioning
properly, removing contaminants from the system.

Vehicles equipped with a desiccant type air dryer that incorporates a filter (separator) for removing oil from the
air will normally minimize oil passed through to the reservoir. The oil collects in the air dryer with condensed
moisture and is periodically purged. Often, the routing or location of the air dryer exhaust port can amplify
concerns about oil passing, depending on where the purged oil / water mixture is expelled on the vehicle, e.g. on a
rear fender or onto a fuel tank. This can mistakenly be identified as “problem” oil passing, when in actuality the
air dryer and compressor are functioning as intended.

Oil Passing & Air Dryers

If excessive oil is passing from the air compressor, the air dryer filter element and desiccant may become
saturated. One of the first signs of an oil saturated filter element or desiccant cartridge is moisture appearing in
the reservoirs. In this case, the air dryer filter element and desiccant need to be serviced and the reason for
excessive water and oil must be determined.

Areas that should be explored are:

* Frequency of reservoir draining.
* Length of time in service; i.e. age of the compressor and desiccant cartridge.
* Brake system maintenance, particularly the leakage of air from the vehicle system.
* Vehicle accessories which may cause high air usage; i.e. air suspension, air wipers, air starters,

kneeling systems, etc.
* Vehicle vocations that may cause high air usage.

Vehicles may be equipped with condensing type aftercoolers or drain valves instead of an air dryer. These devices
have little or no effect on preventing oil or water from being passed through the system and into the reservoir.

FACTORS INFLUENCING OIL PASSING

There are a number of application factors that can influence the oil passing rate of an air compressor, including:

* The inlet air supply.
* The effectiveness of the oil drain from the compressor.
* The coolant flow through the compressor.

Inlet Air Supply

Inlet air normally drawn from one of three locations:

1. Through the engine air cleaner - connected t o the suction side of the turbocharge r.

2. Through a compressor mounted air filter.

3. From the pressure side of the turbocharger.

With methods 1 and 2, strict adherence to recommended filter maintenance schedules is necessary to avoid
introducing excessive restriction and / or inlet contamination, both of which will increase oil passing. Caution
must be exercised in converting a compressor to a turbocharged inlet to avoid causing other serious failure modes.
It is recommended that the vehicle manufacturer or compressor supplier be contacted for approval prior to
converting to turbocharged inlet.

Oil Drain From the Compressor

Restrictions present in the oil drain connection from the compressor to the engine can cause a build up of oil in
the compressor crankcase sump and increased oil passing. Recommendations for oil return lines are discussed on
the attached troubleshooting procedure. For flange mounted compressors which are internally drained back to the
engine, it is important that the drain ports are aligned and not restricted by gasketing or sealant used during the
compressor installation.

On flange mounted compressors, poor drainage may aggravate compressor oil passing. If this is prevalent,
it is recommended to bottom drain the compressor per step 2 of the “Oil Passing Troubleshooting
Procedure”. Bottom cover with drain port is available to convert the compressor.

Coolant Flow

Insufficient coolant flow can promote increased oil passing. Indicators of insufficient cooling include heavy
carbon deposits in the discharge line or fittings, carbonized oil deposits in the inlet cavity and discolo r ation of the
compressor cylinder head. Reference step 4 of the “Oil Passing Troubleshooting Procedure” for compressor
coolant flow requirements.

The attached procedure is intended to assist in determining the p ossible causes when excessive oil passing is
suspected and felt to be air compressor related. If the concern is still present after following this procedure,
consult your local dealer or distributor to determine the manufacturer’s representative in your region for
additional assistance.

Oil Passing Troubleshooting Procedure

STEP 1: Restricted Air Intake

Check engine or compressor air cleaner and replace if necessary. Check compressor air inlet line for kinks,
excessive bends and be certain inlet lines have the minimum specified inside diameter. Recommended minimum
inlet line inside diameter is 5/8” (15.9mm). Recommended maximum air inlet restriction is 25” (6.2kPa) of water.