Crankcase Emissions; Evaporative Emissions - Chevrolet Trailblazer Service Manual

their low flash or ignition temperature point. Such oils burn prematurely during the
combustion process causing emission of particulate matter.
The cooling system is an important factor in the reduction of particulate matter. The
optimum combustion will occur, with the cooling system operating at a temperature
specified by the manufacturer. The cooling system must be maintained in the same
manner as the engine oiling system, as each system is required to perform properly in
order for the engine to operate efficiently for a long time.

Crankcase Emissions

Crankcase emissions are made up of water, acids, unburned fuel, oil fumes and
particulates. These emissions are classified as hydrocarbons (HC) and are formed by the
small amount of unburned, compressed air/fuel mixture entering the crankcase from the
combustion area (between the cylinder walls and piston rings) during the compression and
power strokes. The head of the compression and combustion help to form the remaining
crankcase emissions.
Since the first engines, crankcase emissions were allowed into the atmosphere through a
road draft tube, mounted on the lower side of the engine block. Fresh air came in through
an open oil filler cap or breather. The air passed through the crankcase mixing with blow-
by gases. The motion of the vehicle and the air blowing past the open end of the road draft
tube caused a low pressure area (vacuum) at the end of the tube. Crankcase emissions
were simply drawn out of the road draft tube into the air.
To control the crankcase emission, the road draft tube was deleted. A hose and/or tubing
was routed from the crankcase to the intake manifold so the blow-by emission could be
burned with the air/fuel mixture. However, it was found that intake manifold vacuum, used
to draw the crankcase emissions into the manifold, would vary in strength at the wrong
time and not allow the proper emission flow. A regulating valve was needed to control the
flow of air through the crankcase.
Testing, showed the removal of the blow-by gases from the crankcase as quickly as
possible, was most important to the longevity of the engine. Should large accumulations of
blow-by gases remain and condense, dilution of the engine oil would occur to form water,
soot, resins, acids and lead salts, resulting in the formation of sludge and varnishes. This
condensation of the blow-by gases occurs more frequently on vehicles used in numerous
starting and stopping conditions, excessive idling and when the engine is not allowed to
attain normal operating temperature through short runs.

Evaporative Emissions

Gasoline fuel is a major source of pollution, before and after it is burned in the automobile
engine. From the time the fuel is refined, stored, pumped and transported, again stored
until it is pumped into the fuel tank of the vehicle, the gasoline gives off unburned
hydrocarbons (HC) into the atmosphere. Through the redesign of storage areas and
venting systems, the pollution factor was diminished, but not eliminated, from the refinery
standpoint. However, the automobile still remained the primary source of vaporized,
unburned hydrocarbon (HC) emissions.