If the filter has not been replaced in time and the filter paper is clogged with dirt, then the safety valve opens, bypassing the oil filter, oil supply is ensured.
From the filter, the lubricant enters through the holes in the cylinder block to the lubrication points of the crankshaft, intermediate shaft (4-cylinder engine only) and cylinder heads with camshaft. Through the holes, the oil flows back into the oil pan, from where the oil pump can take it again for the next cycle.
Oil pump
In full load mode, 30 liters of oil passes through the engine per minute:
- In a 4-cylinder engine, the intermediate shaft already mentioned is the drive element for the ignition distributor shaft, which transmits rotation to the oil pump.
- In the 5- and 6-cylinder engines, the oil pump is located in the direction of travel from the front directly on the crankshaft.
The way the oil pumps work in different Audi engines also varies.
The toothed belts of the 4- and 5-cylinder engines are equipped with so-called heat-sensitive tensioners.
Left: Timing belt drive for a 4-cylinder engine.
1 - tension roller;
2 - thermoelement;
3 - toothed belt.
Right: Toothed belt drive for a 5-cylinder engine.
1 - toothed belt;
2 - tension roller;
3 - thermoelement.
- The 4-cylinder engine is equipped with a gear oil pump. Two interlocking gears of the same size simply pump oil from the intake side to the pressure side.
- The 5- and 6-cylinder engines are lubricated by an Eaton system rotary oil pump. Thanks to the rotating gears, the oil is pumped to the outlet side of the pump and from there to the lubrication channels.
Oil temperature
The temperature of the oil is very important for the reliable operation of the engine. This information is only available to the Audi driver via the built-in additional instruments. For comparison purposes, the temperature of the engine oil at the oil filter flange or in the oil pump is of interest; where the oil is coldest. On piston rings, on the other hand, temperatures up to 300°C can prevail. If your car is equipped with an oil thermometer, then you need to remember: Audi shows a temperature of 145°C in the oil pan as the maximum allowable.
However, too low an oil temperature is harmful to the engine. In this case, the oil has not yet reached its full lubricity. Therefore, after a cold start, if possible, you should not accelerate the engine above 3500 rpm until the oil temperature rises to about 60°C. It is estimated that engine oil takes about twice as long as coolant to reach its operating temperature.
Oil pressure
If your car has a built-in oil pressure gauge, then you can check the oil pressure yourself within the accuracy of the measuring instruments. Test conditions: seasonal oil class SAE 20 W/20, oil temperature 80°C. You should get the following stats:
However, the oil pressure in an Audi car is perfectly monitored even without instruments. This is taken care of by two hydraulic switches. You will learn more about this control system in the chapter «Instruments and accessories».
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