Engine Oil: Testing and Inspection
WM 1701IN Information on engine oil consumption
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Causes of engine oil consumption
Every combustion engine uses a normal, system-conditioned amount of lubricating oil. Engine oil is mainly used in the following main areas:
- Pistons with piston rings (interaction with cylinder liners)
- Valve-stem seals in the cylinder head (lubricating oil used in the valve guide)
- Positive crankcase ventilation
- Turbocharger status
Pistons with piston rings (interaction with cylinder liners)/valve stems and valve-stem seals: Minute amounts of engine oil stick to the cylinder walls during each piston stroke. Some of the engine oil is used during combustion and is expelled together with exhaust gases. The effect increases as engine speed increases. For this reason, high-speed engines and turbocharged engines tend to use more engine oil than low-speed engines.
Positive crankcase ventilation: Positive crankcase ventilation carries oil spray (thoroughly atomised fuel) and feeds combustion air back in again. Here, the oil spray passes the oil separator, the main function of which is to filter the oil from the blow-by gases. Oil separation systems work best at a defined gas volume. Oil consumption can increase if the volume is different.
Turbocharger status (position of the turbocharger shaft): Engine oil is supplied to the turbocharger's turbine shaft while the engine is running. During operation, varying amounts of oil get into the combustion gases, depending on the turbocharger status and the driver profile.
Possible causes of increased engine oil consumption
Measurement errors when measuring the oil level =>
- Vehicle is not parked horizontally. The same measuring station is not always used.
- Tyre inflation pressure is very different.
- Vehicle centre of gravity is not consistent (imbalanced load).
- Incorrect engine oil test temperature.
- Engine oil level measured too soon after stopping engine (allow sufficient time for oil to flow back completely into oil pan.).
- Incorrect reading of oil dipstick or instrument cluster.
Important and often disregarded factors relating to engine oil consumption =>
- Driver profile : Vehicles that are used for very sporty driving tend to use more engine oil than vehicles driven normally.
- Driving conditions : Frequent cold starts/driving short journeys result in a higher percentage of fuel in the engine oil (oil is diluted). If the same vehicle is then driven until it gets hot, the fuel in the engine oil evaporates and the engine oil level drops.
- Engine run-in : The components are "run in" during the first 10,000 kilometres/6,000 miles (even in modern engines). This can increase oil consumption. After 10,000 km/6,000 miles, oil consumption should level off to a lower level.
- Engine load : Engine oil consumption can increase during long motorway journeys in the summer, when pulling a trailer, or when driving over high mountain passes for example.
- Loss of engine oil : The engine is leaking and loses oil (possibly onto the underbody panelling).
- Fuel quality : Small amounts of diesel, bio-fuel (ethanol) or bio-diesel in the petrol (e.g. contamination as a result of using the same fuel tanker for diesel/petrol) affect how it enters the oil and how it is evaporated.
Consumption values for analysis purposes
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- If oil consumption is low, the vehicle can be driven further.
- An analysis must be carried out once the specified oil consumption values are reached.
Measuring oil consumption
Measuring oil consumption based on engine-oil refilling capacity
1. Find out about the driver profile, driving conditions, condition of the vehicle, and so on (see above - interview, test drive, make enquiries).
2. Record the mileage, VIN and measurement date.
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Observe the basic rules for measuring the engine oil level:
- Park the vehicle on a level, horizontal surface.
- Check the tyre pressure.
- Do not overload the vehicle (maintain centre of gravity).
- Observe prescribed oil temperature.
- Wait at least 5 minutes after stopping the engine (to allow oil to flow back into the oil pan).
- Pull out the oil dipstick and wipe it off, then insert it back into the guide tube. Pull dipstick out again and read off the oil level.
- Check the engine oil level using the instrument cluster (see relevant operating instructions).
3. Measure the engine oil level in accordance with the "Basic rules for measuring the engine oil level" (original measurement). When taking the original measurement, you must make a sketch of the oil dipstick with the oil level marked.
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Engine oil must not be filled above the "MAX" marking. Too much engine oil can damage the engine and is used up faster due to the dilution effect.
4. Top up oil exactly to the "MAX" marking if necessary.
5. After the customer has driven the vehicle for several hundred kilometres in the course of day-to-day driving, check the engine oil level again in the workshop.
6. Compare the engine oil level with the sketch of the original measurement. Bear in mind the mileage and driving conditions.
7. The amount of oil consumed is the amount of oil that must be added in order to top up the oil exactly to the "MAX" marking. In other words: oil consumption based on mileage driven since the original measurement and amount of oil added.
Measuring oil consumption based on volume measurement
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Oil consumption based on volume measurement can best be measured during an oil change.
1. Find out about the driver profile, driving conditions, condition of the vehicle, and so on (see above - interview, test drive, make enquiries).
2. Record the mileage, VIN and measurement date.
Determine original quantity by recording the oil change refill quantity =>
3. Perform a complete oil change including filter.
Drain engine oil when it is at operating temperature (at least 80 °C). Make sure that the oil-filter housing is completely empty (wait 15 minutes).
4. Determine amount of oil to be filled in (new oil) to the exact millimetre and fill it in (at room temperature of approx. 20 °C). For instructions on changing oil, see -> 170117 Changing engine oil and oil filter Service and Repair or -> 170117 Changing engine oil and oil filter on DFI engines Service and Repair
5. After the customer has driven the vehicle for several hundred kilometres in the course of day-to-day driving, check engine oil consumption in accordance with the following steps.
Determine oil consumption by measuring the remaining oil quantity =>
6. Record the mileage, VIN and date.
7. Drain engine oil into a clean collection container when it is at operating temperature (at least 80 °C). Make sure not to lose any oil (measurement error.). Make sure that the oil-filter housing is completely empty (wait 15 minutes).
8. Let the drained oil cool (room temperature of approx. 20 °C as for first original measurement) and measure the exact oil quantity (in millilitres).
9. The difference between the original filling capacity and the amount of oil you have just drained, depending on the vehicle mileage, gives the oil consumption in kilometres.