Noticeable Symptoms of a Bad Valve Stem Seal

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Noticeable Symptoms of a Bad Valve Stem Seal
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The valve stem seals play a critical role in
controlling valve lubrication as well as oil
consumption.
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These valves regulate the amount of fuel-air
mixture that is allowed in the cylinders for
combustion.
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When the valve stem seal gets damaged, then the
engine will still have good combustion, but there
is more consumption of fuel.
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The high operating temperatures cause the
material to harden and become brittle over time.
And slowly, this will lead to cracking and
complete failure of the valve stem seal.
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Below are some of the noticeable symptoms of a
bad valve stem seal.
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Starting a cold engine
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One of the most noticeable signs of worn valve
stem seals can be observed when you attain to
start a cold engine.
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The top of the cylinder head will be coated with
residual fuel that was pumped up earlier during
running operation.
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The seal has also cooled after an operation,
which causes it to contract and leave a small
gap.
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During idling of the engine
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Bad valve stem seals are more detectable during
prolonged idling at stop signs or stop lights in
congested city conditions.
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When the vehicle sits at idle for prolonged
periods, high levels of vacuum at the intake
manifold result.
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The high vacuum attracts oil in the heads to
congregate around the valve stems. Upon
acceleration, the oil gets sucked past the seal
and down through the valve guide.
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Off-throttle braking
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Evidence of valve seals being compromised will
also show up during off-throttle braking.
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High manifold vacuum, coupled with the downward
slant of the engine, oil collects toward the
front of the valve cover.
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Upon pushing the accelerator after a long coast,
burned oil will exit the tailpipe in large
amounts.
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Faults in spark plug
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Spark plug fouling may occur as oil ash builds up
on the plugs electrodes.
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The accumulation of heavy, oily carbon deposits
on the backs of the intake valves may cause
hesitation and misfires.
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As carbon deposits build up compression may
increase to the point where it causes
engine-damaging detonation.
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More fuel consumption
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Increased fuel consumption due to worn or leaky
valve stem seals will also increase hydrocarbon
(HC) emissions in the exhaust.
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Oil burning can also damage the catalytic
converter because phosphorus in engine oil
contaminates the catalyst.
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If oil is fouling the spark plugs, misfiring can
cause HC emissions to soar. As a result, unburnt
fuel passes into the exhaust.
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