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Oil Consumption of an engine? What is normal?

What has an effect on oil consumption?

We get many questions on what oil consumption is normal - the answer is it depends! What does it depend on? The key points are:

  • Age of the engine (new or old)
  • Its condition
  • The engine loading
  • Its size
  • The grade of oil used

  • Age of engine: A new engine may use a bit more oil until it is run in. Therefore it might be a little higher than its specification sheet. Typically it will be run in after 250 hours.
  • Its Condition: An engine is good condition will use less oil than one that is old and/or badly maintained. For example, if the piston rings are warn, you may notice higher oil consumption as the oil moves past the rings.
  • Engine loading: The engines oil consumption will often be quoted in g/kWh, therefore the higher the running load, the more oil will be consumed. At low load levels (under 30%) for long periods the lower pressure in the cylinders will cause the oil to seep past the piston rings, so at low levels of load, you would expect the amount of oil to increase again from the quoted level.
  • Engine Size: The larger the engine, of course, the more oil it is likely to use.
  • The grade of oil used: If you use a grade of oil that differs from the engine manufacturers recommendations, you might see increased oil consumption. A different grade may cause engine wear leading to shorter engine life and increase oil consumption. You should also use oil only from reputable sources! If you cannot be confident of the source, you cannot be sure you have the right grade, or that its performance will match the required standards.

Example calculation of engine oil consumption

A customer enquires if the Perkins 4012-46TAG2A engine should of used 40L of oil in its first 100 hours of use.

We consult the specification sheet. On it it states:

"After running in (typically after 250 hours) g/kWhr 0.52"

The 4012-46TAG2A engine will produce 1309kWm at prime rating. The average for a prime load should be 70% load factor, so we will use 70% as the figure for calculation, as the customer has not specified a load level. 70% of 1309kWm is 916.3kWm.

Over 100 hours, at 916.3kWm, the oil consumption would be:

916.3 x 100 x 0.52 = 47647 grams.

At 20 degrees C, the density of 15W40 oil is about 0.8787 Kg/L.

So 47647 grams of oil would equate to:

47647 / 0.8787 = 54.225 Litres of oil.

Therefore we can assume that the oil consumption is actually about correct for this engine, as our calculation, based on our assumptions says we should of used more than has actually been consumed.


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