Automotive Systems

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Lubricating System Problem Diagnosis


To troubleshoot an engine lubricating system, begin by gathering information on the problem. Ask the operator questions. Analyze the symptoms using your understanding of system operation. You should arrive at a logical deduction about the cause of the problem.

The four problems most often occur in the lubrication system are as follows:

  1. High oil consumption (oil must be added frequently)
  2. Low oil pressure (gauge reads low, indicator light glows, or abnormal engine noises)
  3. High oil pressure (gauge reads high, oil filter swelled)
  4. Defective indicator or gauge circuit (inaccurate operation or readings)

When diagnosing these troubles, make a visual inspection of the engine for obvious problems. Check for oil leakage, disconnected sending unit wire, low oil level, damaged oil pan, or other troubles that relate to the symptoms.

High Oil Consumption
If the operator must add oil frequently to the engine, this is a symptom of high oil consumption. External oil leakage out of the engine or internal leakage of oil into the combustion chambers causes high oil consumption. A description of each of these problems is as follows:

  • External oil leakage—detected as darkened oil wet areas on or around the engine. Oil may also be found in small puddles under the vehicle. Leaking gaskets or seals are usually the source of external engine oil leakage.
  • Internal oil leakage—shows up as blue smoke exiting the exhaust system of the vehicle. For example, if the engine piston rings and cylinders are badly worn, oil can enter the combustion chambers and will be burned during combustion


Do not confuse black smoke (excess fuel in the cylinder) and white smoke (water leakage into the engine cylinder) with blue smoke caused by engine oil.

Low Oil Pressure
Low oil pressure is indicated when the oil indicator light glows, oil gauge reads low, or when the engine lifters or bearings rattle. The most common causes of low oil pressure are as follows:

  1. Low oil level (oil not high enough in pan to cover oil pickup)
  2. Worn connecting rod or main bearings (pump cannot provide enough oil volume)
  3. Thin or diluted oil (low viscosity or fuel in the oil)
  4. Weak or broken pressure relief valve spring (valve opening too easily)
  5. Cracked or loose pump pickup tube (air being pulled into the oil pump)
  6. Worn oil pump (excess clearance between rotor or gears and housing)
  7. Clogged oil pickup screen (reduce amount of oil entering pump)

A low oil level is a common cause of low oil pressure. Always check the oil level first when troubleshooting a low oil pressure problem.

High Oil Pressure
High oil pressure is seldom a problem. When it occurs, the oil pressure gauge will read high. The most frequent causes of high oil pressure are as follows:

  1. Pressure relief valve struckopen (not opening at specified pressure)
  2. 2. High relief valve spring tension (strong spring or spring has been improperly shimmed)
  3. 3. High oil viscosity (excessively thick oil or use of oil additive that increases viscosity)
  4. 4. Restricted oil gallery (defective block casting or debris in oil passage)

Indicator or Gauge Problems
A bad oil pressure indicator or gauge may scare the operator into believing there are major problems. The indicator light may stay on or flicker, pointing to a low oil pressure problem. The gauge may read low or high, also indicating a lubrication system problem.

Inspect the indicator or gauge circuit for problems. The wire going to the sending unit may have fallen off. The sending unit wire may also be shorted to ground (light stays on or gauge always reads high).

To check the action of the indicator or gauge, remove the wire from the sending unit. Touch it on a metal part of the engine. This should make the indicator light glow or the oil pressure gauge read maximum. If it does, the sending unit may be defective. If it does not, then the circuit, indicator, or gauge may be faulty.


Always check the service manual before testing an indicator or gauge circuit. Some manufacturers recommend a special gauge tester. This is especially important with some computer-controlled systems.

Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy

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