SEAL 9J4753 - Caterpillar

Symptom
The air compressor passes excessive oil. Excessive oil is found in discharge lines. Excessive oil is found at exhaust valves of air system components.Probable Cause
Restricted air inletCheck 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 (1.00 inch) inside diameter for naturally aspirated engines and 15.875 mm (0.625 inch) for turbocharged engines.The maximum value for restriction is 635 mm (25.0 inches) of water.
Restricted oil return to engineThe 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 pressureCheck the engine oil pressure with a test gauge and compare the value 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 size of the coolant line must be determined by the volume of the coolant flow.Check the connections of the coolant lines.The maximum temperature of the coolant at the inlet port is 93 °C (200 °F).The minimum flow of the coolant for the air compressor at the speed of 3000 RPM is 5 L (1.3 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 (3.0 psi) when the brakes are applied.
Excessive engine crankcase pressureTest 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 airCheck 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.