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Instruction of Engine “block oil’ Slobbering From Exhaust Manifold

Nov 27, 2025 | Technical Articles | 0 comments

Recently, we have received feedback from some customers regarding oil leakage observed at the exhaust pipe area during engine operation. Preliminary analysis indicates that this phenomenon is primarily caused by prolonged operation under no-load or light-load conditions. We hereby clarify: All products sold by us are genuine. Chongqing Cummins engines are designed to permit this occurrence under specific operating conditions. This is not a defect in the equipment and may also serve as one reference point for determining whether the machine is operating within reasonable parameters.

 

This article is to help OEM, end users, and as well as other related parties correctly understand the exhaust manifold “block oil” slobbering phenomena while the engine is operating under light or no-load condition, and to guide customers properly use Cummins engine.

 

The designed best performance working condition of Cummins diesel engine is to be operated under rated power condition. Operating the engine for extended periods under light or no-load condition will resulted in:

1.“Block oil” slobbering phenomena the turbocharger area and/or exhaust manifold.

  1. Fuel dilution
  2. Excessive carbon deposit
  3. Lub-oil leakage from turbo compressor

The “Black oil” observed at the exhaust manifold does not only contain engine lub oil,it includes unburned diesel,carbon particle and a few lub oil.

Processing and Recommendations

The operator should always avoid or reduce the time that engine being operated under light or no-load condition. If the engine must be operated under light or no-load condition the period should be limited within 10 minutes according to the O&M manual.

 

The “black oil” appearing at the exhaust pipe is not a pure engine oil leak, but a normal phenomenon under non-ideal operating conditions for diesel engines. This characteristic is inherent to genuine engines under specific operating conditions. We guarantee that the products sold by our company are genuine. Users are advised to strictly follow the specifications outlined in the Operation and Maintenance Manual to ensure the engine operates in optimal condition.

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