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What is included in an oil analysis?

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During a complete oil analysis, you should test the sample for both physical properties and metals. Some of the physical properties tested for and usually included in an oil analysis:

  • Antifreeze. This forms a gummy substance that may reduce oil flow. It leads to high oxidation, oil thickening, high acidity and engine failure if not corrected.
  • Fuel dilution. This property shows that oil has thinned, lowering lubricating ability and potentially causing a drop in oil pressure. This usually causes higher wear.
  • Oxidation. Checking for oxidation is a measure of gums, varnishes and oxidation products. High oxidation from oil that became too hot or was used too long can leave sludge and varnish deposits and thicken the oil.
  • Total base number. This generally indicates the acid–neutralizing capacity still in the lubricant.
  • Total solids. These include ash, carbon, lead salts from gasoline engines and oil oxidation.
  • Viscosity. Viscosity is a measure of an oil’s resistance to flow. Oil may thin due to shear in multiviscosity oils or by dilution with fuel. Oil may thicken from oxidation if it is run too long or too hot. Oil also may thicken from contamination by antifreeze, sugar and other materials.

The following are some of the metals for which oil is tested and some of their potential sources:

  • Aluminum. Thrust washers, bearings and pistons are made of this metal. High readings can be from piston–skirt scuffing, excessive ring–groove wear and broken thrust washers, among other problems.
  • Boron, magnesium, calcium, barium, phosphorous and zinc. These metals normally are from the lubricating oil additive package. They include detergents, dispersants and extreme–pressure additives.
  • Chromium. You typically associate chromium with piston rings. Dirt coming through the air intake or broken rings can cause high levels.
  • Copper and tin. These metals normally come from bearings or bushings and valve guides. Oil coolers also can contribute to copper readings along with some oil additives. In a new engine, these results normally will be high during break–in but will decline in a few hundred hours.
  • Iron. This can come from many places in the engine, such as liners, camshafts, crankshaft, valve train and timing gears.
  • Lead. Lead is associated with bearing wear, but fuel source (leaded gasoline) and sampling contamination (use of galvanized containers for sampling) are critical factors in interpreting this metal.
  • Silicon. High readings generally indicate dirt or fine sand contamination from a leaking air intake system, which cause excessive wear from abrasion.
  • Sodium. You normally would associate high readings of this metal with a coolant leak. But they also can be from an oil additive package.