The air compressor passes excessive oil. Excessive oil is found in discharge lines. Excessive oil is found at exhaust valves of air system components.
- Restricted air inlet
Check the engine air cleaner and replace the air cleaner element, if necessary. Check the inlet line of the air compressor for restrictions and sharp bends. Verify that the air inlet line is the correct size. The minimum size of the air inlet line is 25.4 mm (1.0 inch) inside diameter. The maximum value for restriction is 635.0 mm (25 inches) of water.
- Restricted oil return to engine
The oil return to the engine should not be restricted. Check the oil drain passages in the mounting flange of the air compressor for plugging. Sealant may plug drain holes if sealant was used with a gasket, or if sealant was used instead of a gasket.
- Contaminants are not being drained from air system reservoirs.
Check the reservoir drain valves for proper operation. A vehicle should be equipped with drain valves that are automatic, or all the reservoirs should be drained daily. It is best for the vehicle to have an air dryer with a desiccant cartridge.
- Excessive engine oil pressure
Check the engine oil pressure with a test gauge and compare the reading to the engine specification. When the oil pressure is too high, the oil level in the crankcase of the air compressor may be too high. The oil may not drain into the engine at the same rate as the oil is being pumped into the air compressor.
- The air compressor is too hot.
Remove accumulated debris from the cooling fins of the air compressor. Check for damaged cooling fins. Check for the correct size of the coolant line. The minimum size for a coolant tube is 12.7 mm (0.50 inch) outside diameter. Check the connections of the coolant lines. The maximum temperature of the coolant at the inlet port is 125 °C (257 °F). The minimum flow of the coolant at the maximum speed of 3000 RPM is 9.5 L (2.5 US gal).
- The air compressor is operating under load excessively.
The pressure drop per minute from the air system of the vehicle should not exceed 7 kPa (1.0 psi) when the brakes are not applied. The pressure drop per minute should not exceed 20 kPa (2.9008 psi) when the brakes are applied.
- Excessive engine crankcase pressure
Test for excessive engine crankcase pressure. Replace the components of the crankcase ventilation system or repair the components of the crankcase ventilation system, if necessary. An indication of excessive engine crankcase pressure is a dipstick that is loose or a dipstick that is partially lifted.
- Poorly filtered inlet air
Check for a damaged air cleaner or dirty air cleaner. Check for damaged air inlet components or leaking air inlet components. Check the air piping and fittings.