Simple Site Tests

Simple sensory tests such as appearance, colour and smell will provide an indication of the lubricant condition. A comparison should be made using either a glass bottle or test tube between the used oil and a sample of the original unused oil.

Water or refrigerant contamination will cause the oil to appear hazy. Water content in excess of 0.1% will bubble or crackle when a few drops of the oil placed on a hot plate heated to 120°C.

Darkening of light coloured oils may signify oxidation or contamination with dark coloured products. Used oils from gasoline and diesel engines may show a variety of colours ranging from light brown through red-brown to black. Colour assessment in these cases is not particularly reliable, although an intense brown colour may be indicative of lacquer and a clear black colour indicative of soot rich oils.

An acrid smell with dark colouring and thickening of the lubricant would indicate serious oxidation.

A further simple check of oil degradation is the use of the blotter spot check. This test which is particularly useful for testing engine crankcase lubricants requires a drop of oil deposited on a piece of blotting paper which will show a distinct ring when dry.

• A ring of light debris on the outer circumference of the circular spot indicates that the oil has retained its dispersancy properties.
• A black central spot indicates sludge and the loss of dispersancy.
• A brown or yellow stain on the blotter spot indicates oxidation.
• A white halo around a central deposit indicates the presence of water.

Examination of the system filter is another simple test procedure that is overlooked. The debris trapped by the filter is a historical accumulation of the debris generated by the system. Debris on the filter may be washed with petroleum spirit and examined using a low powered magnifying glass. Identification of the debris will then provide valuable information concerning the operation of that equipment.

The particles of metal found may include one or more of the following: steel, tin, aluminium, silver, copper, bronze, chromium, cadmium or nickel. A visual examination as to colour and hardness will often suffice to identify the metal particles. Positive identification of the metals present may be determined by a few simple tests e.g. a permanent magnet, soldering iron and caustic soda (oven cleaner) - safety standards should be observed.

• Ferrous particles are attracted to the magnet
• White metal or lead will melt on a soldering iron and
• Aluminium will react with caustic soda