ECM BB100, Instruction Manual, Page: 9 / 37

How to Use
Blow-by
Blow-by is the gas flowing out of an engine’s crankcase. If you take off the oil filler cap
when an engine is running, the misty stuff that comes out is blow-by.
Blow-by is primarily caused by the leakage of combustion gases from inside the cylinder into
the crankcase via the piston rings. It also comes from gases leaking past the valve guides or
turbocharger bearings. Blow-by is mostly exhaust gases with a little oil mixed in.
A blow-by meter quantifies how well an engine’s rings, valve guides, and turbocharger
bearings (if the engine has a turbo) are sealing. If an engine is worn out, the rings will leak
and a lot of combustion gases will leak into the crankcase. What is an acceptable blow-by
flowrate depends on the engine’s design and its operating condition (temperature, speed, and
load).
Blow-by information is valuable for:
•
General engine and vehicle testing to ensure that the engine is not excessively worn or
damaged. If an engine has excessive blow-by, it is unlikely that other data taken is
relevant.
•
Engine emissions testing. Blow-by is often recirculated into the intake of the engine and
can affect emissions.
•
Piston ring testing or development. A good ring gives low blow-by.
•
Lubricant testing or development. If the oil doesn’t do its job, the engine will wear out
quickly and blow-by will increase or in some cases decrease due to excessive ring
deposits.
•
Engine durability testing. Blow-by is an excellent indicator of engine condition.
•
Maintaining a fleet of vehicles. When blow-by exceeds a certain value, it’s probably
time to rebuild the engine.
Blow-by can be quantified in two ways:
1. The volume flowrate, in liters per minute (LPM), or cubic feet per minute (CFM) coming
out of the engine at a given engine speed and load (ex. 1500 rpm and no load, or 3000
rpm and maximum load).
2. The total volume of blow-by (in liters or cubic feet) that comes out of the engine while it
executes a driving cycle (ex. FTP cycle).
The BB100 can perform both volume flowrate and total volume blow-by measurements.
Note that it is “volume”, not “mass” being measured. To get mass flowrate measurements,
temperature and pressure transducers need to be installed in the meter (provisions provided)
and the ideal gas law is used.
How to Use 5