What Do You Do With Leftover Engine Oil After Your Oil Change?

How many of us have heard our mechanic say – just as you collect your car after a periodical oil change - “Boss, minyak lebih saya sudah letak dalam boot… you simpan la”.

Most times, there should be a few ounces of oil left at the bottom of your typical 4-litre container (for ease of packaging and market requirements) of oil which your car didn’t need.

Nevertheless, why is it there? And more importantly, what do you do with it?

To understand this we must first understand what engine oil does and how much your car needs.

So what does engine oil do?

Well, you probably already know this, but put simply, engine oil is there to reduce friction and protect your engine’s moving parts. That is it. Engine components – such as the crank assembly, camshafts, and valves – move, rotate, or oscillate at very high speeds when you drive, so it is necessary for them to have sufficient oil to lubricate each part, keep them clean, and reduce wear and tear during operation.

Just how much oil is needed is highly dependent on the type of engine (i.e.: petrol, diesel, hybrid, turbocharged, with or without variable valve timing), and its size (displacement and number of pistons). Typically, the larger or more powerful an engine is – the more lubrication it will need, and hence more engine oil.

The majority of cars sold in Malaysia are naturally-aspirated, four-cylinder, and under 2.0-litres in size; typically these engines would need just under 4-litres of engine oil. However, keep in mind that certain engines, such as turbocharged and six- or eight-cylinder engines typically use (far) more engine oil than the aforementioned 4-litres of oil, but we’ll get back to this.

So what happens with that extra bit of oil?

Typically, nothing. In most cases after your service, you might be left with 50-500ml of unused oil, which your mechanic will tell you to keep in case a top-up is required.

Here is the thing though; your engine – if maintained properly and is in good health – is a sealed system. Therefore, there should be approximately the same amount of oil at the end of the service period, as there was on the first day. Meaning that if you do have to use up that excess oil, it probably means your engine has an oil leak, which needs to be looked at. Therefore, in cases like this where you have to periodically top up your oil – we suppose it makes sense to keep the excess oil and top up your engine oil so it is always at the manufacturer's stipulated level.

However, if you are simply keeping the oil, most leading lubricant manufacturers advise that engine oil – if left unopened in the container and stored at moderate temperatures – have a shelf life of approximately two years. This to guarantee the quality of the oil and its many petroleum-based additives.

So if you have a bit of oil left after your service we can assume that it is probably safe (since the container is already opened), will last another year or so. Now for the purpose of this discussion, let’s assume you buy a 4.0-litre oil pack and only use only 3.5-litres – meaning you can only keep that excess 500 ml for another year or so.

And assuming you change your oil (and use the same oil brand and type) at 7,000km intervals as is stipulated for most semi-synthetic oils – this means you can keep and accumulate these leftovers for use at later service – however, you’d need nearly seven services before you accumulate enough to use all your additional oil. However, by now the oil is probably too old – so why would you want to put it in your engine?!

Honda Malaysia service centres actually have a simple solution, they actually measure and pour just as much as your car needs, and crucially only charge you for that specific quantity. This means that they actually charge you less and there’s no wastage. However, a large majority of manufacturers still sell you 4.0-litre packs during your service.

However, this is isn’t the case with larger engines…

Larger displacement engines, diesel, and turbocharged engines typically use between 5- to 6-litres (even up to 8-litres) of engine oil at every service interval. In this case owners have the option of buying either a single 5- or 6-litre pack of oil (which are limited to a few brands and types), or buy two 4-litre packs of oil – which means you have to purchase 8-litres at one go.

In cases like this, it makes perfect sense to keep your leftover oil – let us say your car uses 6-litres and 2-litres are leftover – one only needs to buy another four-litre pack of oil for the next service and you’re good to go. All you have to do is purchase oil that you know will be available and obtainable when the time comes for your next service.

So if no use to me, why keep it?

This is a perfectly valid question – and note that you can’t just throw your old oil in with the garbage and call it a day. Engine oil should be recycled properly and there are companies that licensed to do this.

Therefore, this is what we advise. Once you’re done with your service, keep the excess engine oil for a period of time, store them in a cool and dry place, and if you don’t use it after the next service or the service after that – give it back to your mechanic. It is highly likely, they will find use for it to top up other cars, and if not, they will recycle it the correct way. At the very least, they are the most convenient point of disposal.

Now if you service your car at a service centre and they don’t take it back from you, you can still do the same by simply passing it back to a nearby workshop for them to dispose of.

If I cannot use it in my car are there any other uses for it?

Well, actually yes, there are many practical uses for engine oil around the house. At its core, engine oil lubricates and keeps out moisture, so there’s no shortage of items that need lubrication at home.

Here are a few uses around the house:

• Use to lubricate creaky gate, door or window hinges – use an old paintbrush to apply engine oil to creaky window or gate hinge.
• Use it to clean your tools – pour your unused engine oil into an old container, and simply dip or drop your DIY tools into the container for a few minutes, remove and wipe dry. Engine oil will ensure your tools are properly lubricated, free from moisture, and shiny to look at.
• Use it on wood items – If you have outdoor furniture and/or structures made of wood, you can simply use an old paintbrush to apply engine oil on the wood surface. Give the engine oil some time to seep into the wood, and wipe off the excess. The oil will serve to keep moisture out of the wood surface, inhibit bacteria and fungi growth, and give the wood surface a nice deep shine. Think of it as cheap wood shellac.
• Use it for your bicycle or garden tools – Use your engine oil to lubricate your bike chain or power tools such as your lawnmower and power drill. Use an old paintbrush or syringe to lubricate rotating parts.

Engine oil has the added benefit of maintaining its viscosity for long periods, hence it will normally last longer than other lubricants such as WD-40 for uses such as this. Again, always remember to dispose of your used oil carefully.