Engine Blow-by – does it need a rebuild?
Engine blow-by is the term used to describe loss of cylinder compression as it leaks past the piston rings into the crankcase.
Blow-by is a direct cause of diesel smoke, oil consumption, loss of compression, and high levels of soot in the lubricating oil.
So, it’s not surprising that it’s a common trigger point for a complete (and expensive) engine overhaul. For a heavy truck engine, this cost could be around $50,000 including downtime, or for a mine haul truck engine it could mean costs of around $300,000 – $400,000 for repairs plus downtime!
Blow-by is usually regarded as an indicator of wear. However, the truth is that in approximately 80% of cases, blow-by is a symptom of piston ring fouling due to carbon accumulation in the piston ring groove, which prevents the ring from forming an effective seal to contain the compression pressure and combustion gases.
Engine blow-by can initially start due to unstable or light-load operating conditions, excessive idling, over-extended service periods, problems with emission control equipment or other reasons.
The longer blow-by continues, the more deposits develop around piston rings, valve gear, emission control equipment, turbochargers and more. Operating performance starts to decline, fuel consumption increases, and eventually catastrophic engine failure can occur. There is generally nothing in recommended maintenance that addresses these deposits , but there is a large window of opportunity to correct this condition before wear and breakdown becomes a serious issue.