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Further Parameters

 

Borderline Pumping Temperature

This is a way of defining operating limits for lubricating (wear) behaviour of engines after cold start. Above the borderline pumping temperature, enough oil flows to the oil screen / oil pump; below this temperature, a sufficient oil supply to the lubricating system may not be provided, so that it would pump air instead of oil.

Maximum borderline pumping temperature according to DIN 51511:

SAE 0W - 40 °C
SAE 5W - 35 °C
SAE 10W - 30 °C
SAE 15W - 25 °C
SAE 20W - 20 °C
SAE 25W - 15 °C

Cold Start Reliability

This parameter lies about 5°C above the borderline pumping temperature and defines the oil temperature at which the starter just can spin the engine at its initial speed.

Pour Point

The pour point is very similar to the previously used solidifying point; indicates the temperature of the flow limit.

Evaporation Loss

The thinner a raffinate, the higher its evaporation loss at operating temperature. Hydro-cracking oils (HC synthesis) and first of all synthetic hydrocarbons (PAO ) are much more convenient in this respect. A high evaporation loss results in a higher oil consumption and carbon deposits on plunger and intake valves. The evaporation loss is determined at 250°C oil temperature over an hour. ACEA  as well as diverse engine manufacturers stipulate threshold values.

The usage of engine oils at low temperatures

The choice of appropriate engine oil is a crucial factor to provide excellent starting up and working characteristics of an engine under low temperatures. The following parameters should be taken into account: oil viscosity and the chemical basis of the oil (base oil).

It depends on the base oil if the end product can be applied under extreme low temperatures e.g. synthetic ester can be used under extreme low temperatures; the application of mineral oils is limited by the temperature of -20°C.

synthetic ester
polyalphaolefins (PAO's)
hydrocrack oils
semisynthetic oils
mineral oils

Society of Automotive Engineers in the USA uses SAE J300 standard to describe the change of viscosity under high and low temperatures.

low temperature viscosity high temperature viscosity
SAE viscosity classes max. viscosity in Pa s at temperature of ... C° viscosity at 100C° in mm2/s
viscosity at 150C°
and high shear rate (106s-1) in mPa s
cranking temperature borderline pumping temperature min max min
0W 6200 at -35 60 000 at -40 3.8
5W 6600 at -30 60 000 at -35 3.8
10W 7000 at -25 60 000 at -30 4.1
15W 7000 at -20 60 000 at -25 5.6
20W 9500 at -15 60 000 at -20 5.6
25W 13 000 at -10 60 000 at -15 9.3
20 5.6 <9.3 2.6
30 9.3 <12.5 2.9
40 12.5 <16.3 2.9
40 12.5 <16.3 3.7
50 16.3 <21.9 3.7
60 21.9 <26.1 3.7
 

The borderline pumping temperature is determined with the help of the cold cranking simulator during the laboratory tests. This is a kind of a rotational viscosimeter that allows measuring the viscosity under low temperatures.

The cranking temperature is calculated by means of adding +5°C to the borderline pumping temperature. This is the maximum temperature for a cold-start. A vehicle in a good technical condition can be started at this temperature without any problems.

Example: engine oil with the viscosity class SAE 5W-40.The borderline pumping temperature for this engine oil is -35°C. +5°C are added. The temperature of a cold start (cranking temperature) is -30°C.

It is very important to take into consideration other aspects that have a negative impact on the borderline pumping temperature:

oil ageing and oil thicknesscaused by the polymerisation

the degree of oil contamination and oil thickness as a result of it

water that penetrates into the oil because of the numerous cold starts or short distance drives

As a conclusion, it is worth to mention that a commonly used explanation of the term “Pour Point” is not absolutely correct. The technical parameter Pour Point doesn’t coincide with the borderline pumping temperature. According to ISO 3016 Pour Point describes the temperature, when the oil is just about moving during the period of 5 sec. while a test tube is being inclined. That means that, the oil is freezing at this temperature. This is a laboratory parameter that should be indicated in the safety pass of the engine oil according to the EU standards. If the temperature of the engine oil achieves Pour Point, the engine can’t be started anymore.

 

 

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