What is the reason for engine oil discharge under the dryer tank?

[VonKaleb]

The condition of engine oil discharge under the dryer tank is caused by damage to the air compressor. When this situation occurs, immediate repair is necessary. Prolonged engine oil discharge under the dryer tank may lead to the following consequences: It may cause the engine to experience a lack of engine oil, which will accelerate engine wear. If there is no engine oil in the engine, the engine cannot operate normally. The functions of engine oil: In the engine, it not only serves as a lubricant but also plays roles in cleaning, sealing, buffering, rust prevention, and heat dissipation. When the engine is running, the engine oil forms a thin film on the surface of various components inside the engine, preventing direct contact and friction between them. Over time, the performance of engine oil will degrade, so it needs to be replaced regularly.

[StCharlie]

I've been driving trucks for long-distance hauls these past few years and have encountered the issue of the air dryer discharging engine oil several times. It's usually caused by problems with the air compressor, such as worn piston rings or cylinder liners, allowing oil to directly enter the air line from the compressor. The compressed air carries the oil into the air dryer, which then drips out from the exhaust port at the bottom. I recommend immediately checking the oil blow-by rate of the air compressor. Disassemble the oil line to see how many milliliters of oil blow-by occur per minute—if it exceeds the standard, you'll need to replace the piston rings or overhaul the compressor. If not addressed promptly, the filter element in the air dryer can become saturated with oil and fail, and oil can accumulate in the brake air reservoir, which is particularly dangerous in winter as it can freeze and block the air lines. A colleague's truck had this issue last time—the brakes suddenly failed on a slope, nearly causing an accident.

[GabrielaFitz]

The most common cause of oil leakage under the dryer tank is due to oil blow-by from the air compressor. If the piston rings are severely worn or the cylinder liner is scratched during compressor operation, engine oil can mix with the compressed air. This oil-laden air enters the dryer tank, where the oil-water mixture fails to separate completely and is naturally discharged through the drain valve. Additionally, check if excessive oil filling has caused excessive crankcase pressure, forcing oil into the air compressor. A rare possibility is the failure of the oil-water separation layer in the dryer tank itself, though this is uncommon. For troubleshooting, first disconnect the oil line to test the oil blow-by rate from the air compressor—if it exceeds 30-40 drops per minute, repairs are needed. Remember to clean the entire air system simultaneously, as residual oil can corrode rubber components.

[JesseLee]

Most cases of oil discharge from the air dryer are caused by compressor oil leakage. When the piston sealing rings of the compressor wear out or there are scratches on the cylinder wall, engine oil from the crankcase gets carried into the compressed air during operation. This oil-air mixture passes through the dryer, where the oil drips out through the exhaust port. The inspection method is quite simple: disconnect the air line between the compressor and dryer, start the engine, and check if oil sprays from the air line opening. If oil is present, it definitely indicates a compressor issue. Occasionally, overfilled engine oil might also cause oil discharge through the breather tube, but this is less likely. Any discovered issues should be addressed promptly, as oil entering the brake system can compromise braking safety.