MerCruiser 305 CID (5.0L) Service Manual page 104

TROUBLESHOOTING
Oil Pressure
Measuring oil pressure
Check engine oil level with boat at rest in
the water
Oil level in crankcase above FULL mark
Oil level in crankcase below ADD mark
Change in oil pressure
Low engine oil pressure at idle
Low engine oil pressure at idle after run-
ning at a high rpm
Boats with dual engines
Boats with dual stations
Index
Page 1C-22
Cause
SERVICE MANUAL NUMBER 24
Special Information
Use a good automotive oil pressure test
gauge. Do not rely on the oil pressure
gauge in the boat.
Oil level should be between the ADD and
FULL marks
May cause loss of engine rpm, oil pres-
sure gauge fluctuation, drop in oil pres-
sure, and hydraulic valve lifter noise at
high rpm
Low oil pressure; oil pressure gauge fluc-
tuation; internal engine noise and/or dam-
age
This may be a normal condition. Oil
pressure may read high in the cooler times
of the day and when engine is not up to
operating temperature. As the air tempera-
ture warms up and engine is operating at
normal temperature, it is normal for oil
pressure to drop.
With modern engines and engine oils, low
oil pressure readings at idle do not neces-
sarily mean there is a problem. If valve lift-
ers do not "clatter" (at idle), there is a suffi-
cient volume of oil to lubricate all internal
moving parts properly. The reason for the
drop in oil pressure is that engine heat
causes an expansion of the internal toler-
ances in the engine and the oil will thin out
somewhat from heat.
Refer to preceding.
It is not uncommon to see different oil
pressure readings between the two en-
gines, as long as both engines fall within
specifications. Differences in oil pressure
can be attributed to differences in engine
tolerances, gauges, wiring, senders, etc.
Refer to Boats with Dual Engines, above.
90-861327--1 OCTOBER 1999