What happens to used oil when it's replaced? | AutoGuru
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What happens to used oil when it's replaced?

Rachel White

Updated 11 Oct 2019

Rachel White

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Oil keeps car engines and other machines running smoothly. Moving parts create friction and heat and oil is required to create a lubrication layer between moving parts and to disperse heat effectively.

When oil moves through an engine it picks up impurities such as water, chemicals and dirt. Over time, this causes the oil to become less effective and, if left indefinitely, this can lead to engine damage. This is why engine oil needs to be replaced at regular intervals.

In Australia, more than 500 million litres of engine oil is purchased every year. A vehicle will be serviced on average one to two times per year, depending on how many km’s driven and every time it is serviced around four to five litres of oil is replaced. That’s a lot of used oil!

How to dispose of engine oil
Used oil can contain hazardous contaminants and has the potential to be a nasty pollutant, not only waterways but also the ground around us. It is slow to degrade, sticks to everything and is insoluble. This is why oil has to be disposed of appropriately. Oil isn’t something that can be thrown away, poured down a drain or dumped on the garden.


Can they be recycled?

Never throw away used engine oil or sump oil. If you have used oil, place it in a leak-proof container and take it to a used oil recycling facility. Council transfer stations accept used oil and may even take your used oil filters and oily rags too. Automotive workshops will usually accept your used engine oil as well, taking it off your hands and adding it to their used oil storage. Workshops store used oil and arrange for its collection on a regular basis.

Local authorities and automotive workshops are required to manage the handling of used oil properly to make sure it doesn’t have any environmental impact.

How is used oil recycled?

Used oil can actually be cleaned and reused. The oil is refined into new oil, fuel oils, lubricants and used for raw materials. The used oil also contains metal which can be recycled. The recycling process is:

Dewatering the oil

: This process splits the free water from the oil. Extracted water goes to waste water treatment.

Filtering and Demineralisation

: Filters remove inorganic materials and unwanted additives. The first stage waste extracted includes acid, oil contaminants, additives and metals. Second stage waste removes fine particles.

Propane De-asphalting

: This is a pre-treatment step. This produces a de-asphalting lube oil. Propane is used to separate insoluble material. The propane is used, recovered and reused in this process.


: This stage uses a boiling process to separate components of the oil. Removed components are hydrocarbons (gases, petrol and solvents). This is done via atmospheric and/or by a vacuum method. The vacuum method will separate the oil into levels of light, medium and heavy oil. Any remaining additives and contaminants that make it to this stage will be separated from the finished refined oil.

Used oil goes through the same refining standards as virgin oil and is refined and transformed back into high-quality lubricating oil. This process can happen over and over again and means the oil that was removed from your car at its last service might be reused as new, refined oil for the next one. Now that’s how recycling is done!

Rachel White

Written By

Rachel White

Rachel spent her early adult life around cars, motorsport and hands-on with her own cars. This interest moved into various careers within the Automotive industry. Joined with her passion for writing, Rachel loves putting the two together to share her experience, so we can all become AutoGuru’s.