| Tools Needed | Quantity | |
| 8T-2700 | Blowby/Air Flow Indicator | 1 |
Note: For a new G3304 Engine that is operating at 1800 rpm, the typical crankcase blowby is approximately
Measure the crankcase blowby of an engine after approximately 250 hours of operation. Record the data as a benchmark. Continue to periodically measure the blowby. Comparing the recorded data to the new data provides information about the condition of the engine.
Note: Crankcase blowby is one of the three factors that help to determine the major overhaul interval. Refer to Operation and Maintenance Manual, "Overhaul (Major)".
After a new engine is used for a short time, the blowby can decrease as the piston rings are seated. The blowby will gradually increase as the piston rings and cylinder liners show wear. More fumes are exhausted through the crankcase breather. The crankcase breather will become clogged more rapidly. Excessive crankcase pressure can also cause engine oil to leak at the gaskets and the seals.
The blowby of a worn engine may exceed the blowby of a new engine by two times or more.
Note: A problem with the piston rings causes the engine oil to deteriorate rapidly. Information regarding the condition of the piston rings can be obtained from the measurement of the blowby and the results of an analysis of the engine oil.
A sudden increase in blowby could indicate a broken piston ring. This condition will cause the engine to run rough. The following conditions are other potential sources of blowby:
- Worn valve guides
- A turbocharger seal that leaks
A rebuilt engine can have a high blowby due to the following factors:
- The piston rings are not seated properly.
- Worn parts such as valve guides were not replaced.
By keeping a record of the results, a gradual increase in the amount of the blowby will be noted until the amount has become excessive.
To measure the blowby, use the 8T-2700 Blowby/Air Flow Indicator. Refer to Special Instruction, SEHS8712, "Using the 8T-2700 Blowby/Airflow Indicator Group". The instruction is provided with the tool.
Keep a record of the results.