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Knowledge Centre / FAQ


Application & Useful Information

 

Miscibility of Engine Oils

Basically, engine oils are supposed to be miscible with each other, no matter if they are synthetic or mineral. Such is the claim made by automotive firms. However, engine oils of different brands or formulations should only be mixed if there are no other possibilities for replenishment at hand.

It is not recommended to mix synthetic and mineral engine oils, because thereby the rather higher quality of synthetic oils would be reduced. The reached quality is just as good as the weakest link in the chain.

Oil Consumption

1. Mechanical causes (construction of the engine)
  • Design of piston rings: piston rings clearance --> stroke clearance, slot clearance, ring tension
  • Valve stem clearance, valve stem seal clearance
  • Crankcase ventilation system
  • Breaking-in stage of the engine – piston rings are in a hinge position not sooner than the breaking-in process is over
  • Leakage
  • Defect cooling system due to extremely high operating temperatures
  • General operating conditions
2. Physical/chemical causes (engine oil formulation)
  • Tendency to strong evaporation at high temperatures
  • Fuel dilution --> decrease in viscosity (slippage and evaporation losses)
  • High frothing tendency
  • Strong oxidation
  • Too much oil filled in
  • Decrease in viscosity due to mechanical stress (viscosity loss due to the shearing strain)

Drop in Oil Pressure

1. Construction-conditioned and mechanical causes
  • Capacity fault or malfunction of the oil pump
  • Advanced engine wear (bearings clearance)
  • Dimensioning of oil supply tubes
  • Very low revolutions at idle running
  • Positioning, function, and precision of the oil pressure sensor
  • Very high ratio of oil in engine (e.g. sump construction)
  • Defect cooling system due to extremely high operating temperatures
2. Engine oils and extern influences
  • Too heavy shearing strain (drop in viscosity)
  • Extreme dilution of fuel
  • High water content in oil --> bubbles and froth developing
  • Strong frothing – high rate of trapped air
  • Congestion (oil)
  • Overheating of engine oil (e.g. defect cooling system)

Frothing

  • Engine congestion causes high mechanical stress for oils --> trapped air
  • Too much water in oil (bubbles emerge at high temperatures)
  • Oils with poor air-releasing properties
  • Heavy oil contamination
  • High degree of oil dilution by fuel

Heavy oil frothing increases wear and thus causes overheating. The oil supply can break down altogether if the oil pump operates in the “dry mode”. Especially hydraulic slides are very sensible to heavy frothing.

In the oil supply tubes, the trapped air can cause malfunctioning and imperil pressure equalisation (noises). Bubbles in oil can also cause damage of materials, e.g. on large end bearings. Another aspect is the so-called cavitation (under high pressure, air bubbles implode and cause severe damage of the surrounding material).

Some thoughts about engines with high mileage: if such engines (mileage of 60,000 – 100,000 km and more) operate with mineral oil, carbon deposits (e.g. on piston rings or valve guides) can develop over the years. The engine is likely to be polluted, because mineral oils are thermally less stable than synthetic ones.

Due to the rinsing and cleaning effects of some synthetic engine oils, carbonisation and deposits are being removed by and by. Since the cleaning process in an engine does not take place simultaneously and homogeneously, higher oil consumption is possible during the transitional period. The oil consumption, e.g. in the piston rings area, will normalise after the rings are rinsed clean and clear.

In case of a heavy pollution it is recommended to clean the engine with a special engine cleaner. There is no danger that deposits will be removed all at once and block the oil supply system.

Storage of Engine Oils

Every lubricant should possibly be stored in closed and dry rooms and at a constant temperature. When stored inappropriately (extreme temperature fluctuations, high humidity), oils can absorb moisture because of “package respiration”. Packages are indeed impervious to fluids, yet not to gases.

Water can cause clouding of oil and not least precipitation. In addition, the products should preferably be stored at temperatures above 0°C. Oils in plastic packages can age under permanent direct sunlight (UV light).

 

 

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