* Engine design and age: Older designs or engines with significant wear will naturally have higher blow-by than newer, well-maintained ones.
* Operating conditions: High-load, high-temperature operation will increase blow-by.
* Measurement method: Different methods of measuring blow-by (e.g., volume per hour, pressure differential) yield different results, making direct comparisons difficult. The *method* used is crucial for interpreting the results.
* Specific manufacturer's specifications: The best reference point is the engine manufacturer's specifications for acceptable blow-by. Their service manuals usually provide guidelines, often expressed as a rate or pressure relative to engine speed or load.
Instead of looking for a single "good" number, focus on these:
* Consistent readings: A suddenly increasing blow-by rate is a much more significant concern than a consistently slightly elevated reading. Consistent slightly high blow-by might be the result of normal wear, while a rapid increase points to a problem that needs attention.
* Comparison to baseline: If you've measured blow-by before, comparing current readings to the baseline is more meaningful than comparing to a generic number from the internet.
* Symptoms: Look for other related problems like excessive oil consumption, blue exhaust smoke (indicating burned oil), or loss of compression. These symptoms, along with a rising blow-by measurement, give a clearer picture of the engine's health.
In short: You need to consult the engine's service manual for acceptable blow-by limits. A qualified diesel mechanic can properly measure blow-by and interpret the results in the context of the engine's overall condition. Relying on a general number without considering the specific engine and testing methods is unreliable and potentially dangerous.
