Excessive Oil Consumption; Oil Pressure Diagnosis And Testing - GMC Powertrain 4.3 L Service Manual

Engine
Excessive oil consumption (not due to leaks) is the use
1.9 liters (2 quarts) of engine oil within 3,200 kilometers
(2,000 miles). However, during initial engine break-in
periods 4,828-6,437 kilometers (3,000-4,000 miles) oil
consumption may exceed 1.9 liters (2 quarts) or more.
The causes of excessive oil consumption include the
following conditions:
• External oil leaks. Tighten the bolts and/or
replace gaskets and oil seals as necessary.
• Incorrect oil level or improper reading of oil
level indicator. With the vehicle on a level
surface, allow adequate drain down time and
check for the correct oil level.
• Improper oil viscosity. Use a recommended
SAE viscosity for the prevailing temperatures.
• Continuous high speed operation and/or
severe usage.
• Crankcase ventilation system restrictions or
malfunctioning components. Possible improper
PCV valve.
• Valve guides and/or valve stem oil seals worn,
damaged or the seal omitted. Ream the valve
guides and install oversize service valves and/
or new valve stem oil seals.
• Piston rings broken, improperly installed, worn
or not seated properly. Allow adequate time for
the piston rings to seat. Replace broken or
worn piston rings as necessary.
• Piston improperly installed or mis-fitted.

Oil Pressure Diagnosis and Testing

1. With the vehicle on a level surface, allow
adaquate drain down time (2-3 minutes) and
measure for a low engine oil level.
Add the recommended grade engine oil, and fill
the crankcase until the oil level measures FULL
on the oil level indicator.
2. Operate the engine and verify low or no oil
pressure on the vehicle oil pressure gauge or the
oil indicator light.
Listen for a noisy valve train or a knocking noise.
3. Inspect for the following:
• Engine oil diluted by moisture or unburned fuel
mixtures
• Improper engine oil viscosity for the expected
temperature
• Incorrect or faulty oil pressure gauge sensor
• Incorrect or faulty oil pressure gauge
• Plugged oil filter
• Malfunctioning oil filter bypass valve
Marine/Industrial 4.3L 6-15
4. Remove the oil pressure gauge sensor or
another engine block oil gallery plug.
5. Install an oil pressue gauge.
6. Start the engine and then allow the engine to
reach normal operation temperature.
7. Measure the engine oil pressure at the following
RPM:
Specification
7.1. 42 kPa (6psig) (minimum) at 1,000 RPM
7.2. 125 kPa (18 psig) (minimum) at 2,000 RPM
7.3. 166 kPa (24 psig) (minimum) at 4,000 RPM
8. If the engine oil pressure is below minimum
specifications, inspect the engine for one or
more of the following:
• Oil pump worn or dirty
• Malfunctioning oil pump pressure relief valve
• Oil pump screen loose, plugged or damaged
• Excessive bearing clearance
• Cracked, porous or restricted oil galleries
• Engine block oil gallery plugs missing or
incorrectly installed
• Broken valve lifters
2000 Marine/Industrial