myoldboat2
Petty Officer 1st Class
- Joined
- Jun 3, 2007
- Messages
- 303
1974 GM Engine 140 HP 4-cyl 181 cu.in.
Mercruiser "Late Model I" Stern Drive
Engine starts easily. Oil pressure takes a while to come up--it takes maybe 10 seconds to climb up out of the red arc. At idle it is down near the red arc, maybe 22 psi. As the rpm increases the oil pressure increases. Running on the lake at WOT, oil pressure is about 50 or 55 psi. At typical cruising speeds it is about 40 psi.
The 22 psi at idle seems low? This is even when the engine is cold, when I would think the oil pressure would read high until it warms up.
The oil & filter were changed about 4 running hours ago. Maybe the sending unit or gauge are bad. If the oil pump needs replacing, where is it and is it a big job?
What do you guys think?
This is from the Mercruiser Repair Manual:
Oil Pressure
1. Measuring oil pressure
1. Use a good automotive oil pressure test gauge.
Do not rely on the oil pressure gauge in the boat.
2. Check engine oil level with boat at rest in the
water
2. Oil level should be between the ADD and FULL
marks
3. Oil level in crankcase above FULL mark
3. May cause loss of engine RPM, oil pressure
gauge fluctuation, drop in oil pressure, and hydraulic
valve lifter noise at high RPM
4. Oil level in crankcase below ADD mark
4. Low oil pressure; oil pressure gauge fluctuation;
internal engine noise and/or damage
5. Change in oil pressure
5. 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 temperature warms up and engine is running
at normal opening temperature, it is normal for oil
pressure to drop.
6. Low engine oil pressure at idle
6. With modern engines and engine oils, low oil
pressure readings at idle do not necessarily mean
there is a problem. If valve lifters do not ?clatter?
(at idle), there is a sufficient 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 tolerances in
the engine and, also, the oil will thinout
somewhat from heat.
7. Low engine oil pressure at idle after running at a
high RPM
7. Refer to No. 5 and 6, preceding
8. Boats with dual engines
8. It is not uncommon to see different oil pressure
readings between the two engines, as long as
both engines fall within specifications. Differences
in oil pressure can be attributed to differences in
engine tolerances, gauges, wiring, senders, etc.
9. Boats with dual stations
9. Refer to No. 8. preceding
Low Oil Pressure
Cause / Special Information
1. Low oil level in crankcase
2. Defective oil pressure gauge and/or sender
2. Verify with an automotive test gauge. Refer to
SECTION 4D for instrument testing.
3. Thin or diluted oil
3. Oil broken down; contains water or gas; wrong
viscosity; engine running too hot or too cold;
excessive idling in cold water (condensation)
4. Oil pump
4. Relief valve stuck open; pickup tube restricted;
worn parts in oil pump; air leak on suction side of
oil pump or pickup oil tube
5. Oil leak can be internal or external
5. Oil passage plugs leaking, cracked or porous cylinder
block
6. Excessive bearing clearance
6. Cam bearings, main bearings, rod bearings
Mercruiser "Late Model I" Stern Drive
Engine starts easily. Oil pressure takes a while to come up--it takes maybe 10 seconds to climb up out of the red arc. At idle it is down near the red arc, maybe 22 psi. As the rpm increases the oil pressure increases. Running on the lake at WOT, oil pressure is about 50 or 55 psi. At typical cruising speeds it is about 40 psi.
The 22 psi at idle seems low? This is even when the engine is cold, when I would think the oil pressure would read high until it warms up.
The oil & filter were changed about 4 running hours ago. Maybe the sending unit or gauge are bad. If the oil pump needs replacing, where is it and is it a big job?
What do you guys think?
This is from the Mercruiser Repair Manual:
Oil Pressure
1. Measuring oil pressure
1. Use a good automotive oil pressure test gauge.
Do not rely on the oil pressure gauge in the boat.
2. Check engine oil level with boat at rest in the
water
2. Oil level should be between the ADD and FULL
marks
3. Oil level in crankcase above FULL mark
3. May cause loss of engine RPM, oil pressure
gauge fluctuation, drop in oil pressure, and hydraulic
valve lifter noise at high RPM
4. Oil level in crankcase below ADD mark
4. Low oil pressure; oil pressure gauge fluctuation;
internal engine noise and/or damage
5. Change in oil pressure
5. 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 temperature warms up and engine is running
at normal opening temperature, it is normal for oil
pressure to drop.
6. Low engine oil pressure at idle
6. With modern engines and engine oils, low oil
pressure readings at idle do not necessarily mean
there is a problem. If valve lifters do not ?clatter?
(at idle), there is a sufficient 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 tolerances in
the engine and, also, the oil will thinout
somewhat from heat.
7. Low engine oil pressure at idle after running at a
high RPM
7. Refer to No. 5 and 6, preceding
8. Boats with dual engines
8. It is not uncommon to see different oil pressure
readings between the two engines, as long as
both engines fall within specifications. Differences
in oil pressure can be attributed to differences in
engine tolerances, gauges, wiring, senders, etc.
9. Boats with dual stations
9. Refer to No. 8. preceding
Low Oil Pressure
Cause / Special Information
1. Low oil level in crankcase
2. Defective oil pressure gauge and/or sender
2. Verify with an automotive test gauge. Refer to
SECTION 4D for instrument testing.
3. Thin or diluted oil
3. Oil broken down; contains water or gas; wrong
viscosity; engine running too hot or too cold;
excessive idling in cold water (condensation)
4. Oil pump
4. Relief valve stuck open; pickup tube restricted;
worn parts in oil pump; air leak on suction side of
oil pump or pickup oil tube
5. Oil leak can be internal or external
5. Oil passage plugs leaking, cracked or porous cylinder
block
6. Excessive bearing clearance
6. Cam bearings, main bearings, rod bearings
