Maneuvering; Operation At Low Load - Volvo Penta D8 2020 Operator's Manual

Operation
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Maneuvering

Operation at low load

Avoid long-term operation at idle or at low load. It takes
a long time for the engine to reach working
temperature, resulting in high viscosity of the oil and
large clearances in the engine mechanics. In cold
climate, it takes even longer.
The combustion temperature and cylinder pressure
can become so low that an effective combustion
cannot be ensured. At these conditions unburned fuel
could dilute the lubricant oil. Because of the low
cylinder pressure, the piston ring performance could
be affected causing oil from the crankcase to pass the
rings and go further out with the exhaust gases. This
mixture of unburned fuel and oil in exhaust gases is
referred to as "slobber". A new engine produces more
"slobber" at low load compared to an engine with more
hours of operation.
At low load, the pressure in the turbocharger is low and
oil could seep past the turbocharger seals and mix with
the air into the engine. The consequences can be
carbon build-up on valves, piston crowns and the
exhaust turbine, which could affect engine
performance.
Both conditions can lead to increased oil consumption
and eventually external oil leakage from joints in the
exhaust system. For example, leakage could be seen
at the exhaust manifold, before and after the turbo,
around the muffler and in worse case even in the
exhaust end pipe. Consequences could lead to
clogged exhaust gas recirculation systems and
exhaust aftertreatment systems.
Signs of oil leaking caused by "slobber" do not indicate
an engine problem but indicates low load operation. To
minimize the risk of malfunctions caused by operation
at low load, follow these points as a complement to
normal maintenance:
• Run in the engine as soon as possible.
• Load the engine so it reaches working temperature
as soon as possible.
• For VE: Turn off the engine instead of running on
idle for longer periods.
• For genset turn off the engine instead of running
unloaded for longer periods.
• Avoid load levels below 20% as constant operation.
• If the engine is regularly tested without load, limit the
duration of the operation to 5 minutes. Run the
engine at full load for about 4 hours once a year, for
the carbon deposits in the engine and exhaust
system to burn off.
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