TROUBLESHOOTING
SERVICE MANUAL NUMBER 23
Page 1C-21
90-861326--1 MARCH 1999
Excessive Oil Consumption
Cause Special Information
Normal consumption.
One quart of oil consumed in 5-15 hours
of operation at wide-open-throttle (espe-
cially in a new or rebuilt engine) is normal
Oil leaks
Clean bilge, run engine with clean white
paper on bilge floor, locate oil leak(s)
Oil too thin Oil diluted or wrong viscosity
Oil level too high
Drain holes in cylinder head plugged Oil will flood valve guides
Defective valve seals
Intake manifold gasket leaking
Worn valve stems or valve guides
Defective oil cooler (if equipped) Crack in cooler tubes
Defective piston rings
Glazed, scuffed, worn, stuck, improperly
installed; ring grooves worn; improper
break-in; wrong end gap
Defective cylinders
Out of round, scored, tapered, glazed;
excessive piston to cylinder clearance;
cracked piston
Excessive bearing clearance
NOTE: 454 Mag MPI and 502 Mag MPI: ENGINE CRANKCASE OIL MUST BE CHECKED
AT INTERVALS SPECIFIED IN “MAINTENANCE SCHEDULE”. It is normal for an engine
to use a certain amount of oil in the process of lubricating and cooling the engine Oil
consumption will be higher on the 454 Mag MPI and 502 Mag MPI. These engines utilize
forged (rather than cast) aluminum pistons to withstand the higher stresses created by their
higher horsepower output. The forged pistons require increased piston-to-cylinder bore
clearance to accommodate their higher thermo-expansion rate and thus, it is normal for
some oil to get past the piston rings and be burnt-up in the combustion chambers. The
amount of oil consumption is greatly dependant upon engine speed, with consumption
being highest at wide-open-throttle and decreasing substantially as engine speed is
reduced. It is not uncommon for big block high performance engines to use up to 1 quart
of oil in 1-5 hours if the engine is operated continuously at the upper end of the rpm range.
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