MerCruiser 305 CID (5.0L) Service Manual page 108

TROUBLESHOOTING
Water on Top of Pistons
Operator shut engine off at high rpm
Engine "diesels" or tries to run backwards
NOTE: The term "diesel" refers to an engine's tendency to run on after the key has been
turned to the OFF position.
Rain water running into flame arrestor
Spark plug misfiring
Backwash through the exhaust system
Improper engine or exhaust hose installa-
tion
Cracked exhaust manifold
Improper manifold to elbow gasket instal-
lation
Loose cylinder head bolts
Blown cylinder head gasket
Cracked valve seat
Porous or cracked casting
Water in Crankcase Oil
Water in boat bilge
Water seeping past piston rings or valves
Engine running cold
Intake manifold leaking near a water pas-
sage
Cracked or porous casting
Index
Page 1C-26
Cause
Cause
SERVICE MANUAL NUMBER 24
Special Information
Engine out of tune, poor fuel, high idle
rpm, timing set too high
Hatch cover
Improper combustion causes moisture in
the air to accumulate in the cylinder
Check for warped cylinder head or cylin-
der block
Check cylinder heads, cylinder block, and
intake manifold
Special Information
Boat has been submerged or bilge water
was high enough to run in through dipstick
tube
Refer to "Water on Top of Pistons"
Defective thermostat, missing thermostat;
prolonged idling in cold water
Check cylinder head, cylinder block and
intake manifold
90-861327--1 OCTOBER 1999