Overfilled Crankcase; Checking Engine Oil Level/Filling - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Overfilled Crankcase

Overfilled crankcases (oil level being too high) can cause a fluctuation or drop in oil pressure
and rocker arm "clatter" on MerCruiser engines. The over-full condition results in the engine
crankshaft splashing and agitating the oil, causing it to foam (become aerated). The aerated
oil causes the hydraulic valve lifters to "bleed down." This, in turn, results in rocker arm
"clatter" and loss of engine performance, due to the valves not opening properly.
Care must be taken when checking engine oil level. Oil level must be maintained between
the ADD mark and the FULL mark on the dipstick. To ensure that you are not getting a "false
reading," make sure the following steps are done before checking the oil level.

Checking Engine Oil Level/Filling

IMPORTANT: ENGINE CRANKCASE OIL MUST BE CHECKED AT INTERVALS
SPECIFIED IN "MAINTENANCE SCHEDULE" CHART. It is normal for an engine to use
a certain amount of oil in the process of lubrication and cooling of the engine. The
amount of oil consumption is greatly dependent upon engine speed, with
consumption being highest at wide-open-throttle and decreasing substantially as
engine speed is reduced.
454 cid / 7.4L and 502 cid / 8.2L: These engines have forged pistons to handle the higher
operating stresses of these engines. These engines normally use 1 U.S. quart (0.9 L) of oil
in 1 - 5 hours of running at or near full throttle.
1. Stop engine and allow boat to come to a rest.
2. Allow oil to drain back into oil pan -approximately 5 minutes.
3. Remove dipstick. Wipe clean and reinstall. Push dipstick all the way into dipstick tube.
4. Remove dipstick and note the oil level.
5. Oil level must be between the FULL and ADD marks.
6. If oil level is below ADD mark, proceed to Steps 7 and 8.
Index Index
90-861326--1 MARCH 1999
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Boat "at rest" in the water, or:
If boat is on a trailer, raise or lower bow until the boat is sitting at the approximate angle
that it would be if sitting "at rest" in the water.
Allow sufficient time for oil to drain into the crankcase if engine has just been run or oil
has just been added.
MIE Shown (MCM Is At Front Of Engine)
a - Oil Dipstick
b - Add Mark
a
70775
MAINTENANCE
b
70543
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