Low Engine Temperature; Low Engine Oil Pressure; Water In The Engine; Important Information - Mercury MerCruiser Service Manual

Possible Cause
Seawater discharge restricted or plugged.

Low Engine Temperature

Possible Cause
Faulty thermostat.

Low Engine Oil Pressure

Possible Cause
Insufficient oil in the crankcase.
Excessive oil in the crankcase (causing it to
become aerated).
Diluted or improper viscosity oil.
NOTE: Refer to PCM 112 Diagnostic Manual for more information.

Water in the Engine

Important Information

IMPORTANT: First determine the location of the water in the engine. This information can be of great help when trying to
determine where the water came from and how it got into the engine. The three most common problems are water on top of the
pistons, water in the crankcase oil, and when both of those conditions occur simultaneously.
1. After locating the water, remove all the water from the engine by removing all the spark plugs and cranking the engine over
to pump out the cylinders.
2. Change the oil and the filter.
3. Start the engine and see if the problem can be duplicated. If the problem can be duplicated, a mechanical problem exists. If
the problem cannot be duplicated, the problem is either an operator error or a problem that exists only under certain
environmental conditions.
If the water is contained to the cylinders only, it is usually entering through the exhaust system. If the water is contained to the
crankcase only, it is usually caused by water entering through the intake manifold, a flooded bilge, or condensation. If the water
is located in both the cylinders and the crankcase, it is usually caused by water in the cylinders getting past the piston rings and
valves or complete submersion. Checking for water trails in the intake manifold or the exhaust manifolds is a good idea. Water
trails are a clue that water entered these areas.
Symptom
1. Water on top of
the pistons.
2. Water in the
crankcase oil.
90-8M0099748 eng DECEMBER 2015
Check and add oil.
Check and remove the required amount of oil. Check for the cause of excessive
oil (improper filling).
Change the oil and oil filter, using the correct grade and viscosity oil. Determine
the cause for dilution (excessive idling).
Cause
1.0 The operator shut the engine off at
a high RPM.
1.1 Water ingestion through the
exhaust system.
1.2 Improper engine or exhaust hose
installation.
1.3 Cracked exhaust manifold.
1.4 Corroded exhaust elbow.
1.5 Loose cylinder head bolts.
1.6 Blown cylinder head gasket.
1.7 Cracked valve seat.
2.0 Water in boat bilge.
2.1 Engine stored outside, or with the
engine cover missing.
2.2 Intake manifold leaking near a
water passage.
2.3 Cracked or porous casting.
Clean exhaust elbows.
Replace the thermostat.
1.0 Refer to Section 3 ‑ On the Water in the Operation,
Maintenance and Warranty Manual.
1.1 Verify the exhaust elbow height. Repair the exhaust
system.
1.2 Check the engine installation specifications.
1.3 Replace the exhaust manifold.
1.4 Replace the exhaust elbow.
1.5 Tighten the cylinder head bolts.
1.6 Determine the cause of the blown gasket and replace the
gasket.
1.7 Replace the valves.
2.0 Drain the water from the bilge.
2.1 Ensure the engine is properly covered.
2.2 Inspect the intake manifold for cracks. Check the gaskets.
2.3 Check the cylinder head, the cylinder block, and the intake
manifold for cracks or porosity.
© 2016 Mercury Marine
Engine Troubleshooting
Remedy
Remedy
Remedy
Action
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