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  How to check & top up your engine oil

In this aricle: Some background on what engine oil does, what oil you need to buy, how to check your oil and how to top it up.

On this page: Background | What to buy | Checking your oil level | Top up your oil

First, a little bit of background...

An engine oil check should be top of your car maintenance checklist. Oil covers the moving metal parts of the engine with a thin film, allowing them to slip freely past each other. lt also helps keep the engine cool and cleans away the dirty deposits that are left behind when fuel is burnt.

TOP TIP: Engine oil only fully protects the engine when it’s warmed up. Revving the car too hard in the first few miles of your journey will cause unnecessary wear and tear and shorten the life of the engine.

Engine oil plays a vital role in determining the life span of an engine, so as well as being topped up it needs to be changed regularly or eventually it turns into a gloopy sludge. A filter is used to trap all the deposits collected by the engine oil and must be changed at the same time.

Although modern cars tend to use less oil than older ones, they still need checking regularly between services. The rate at which an engine uses oil will vary from car to car but some can use a litre or more in between servicing.

If an engine gets low on oil it wears out faster and can also suffer from overheating problems. If left to run very low it may seize up altogether and leave you with a big bill for a new engine.

Can I just top up when the oil light comes on?

The low oil warning light tells you there isn’t enough oil to protect the engine so don’t use it as your reminder to top up. Aim to give your oil level a quick check every other time you fill up with fuel.


Engine oil comes in three main types; mineral, synthetic and semi synthetic. Most modern cars will use one of the latter two which are known as ‘multi-grade’ and means their thickness is different depending on the temperature. The oil is thinner when cold so when you first start the car it flows more easily and protects the engine faster.

TOP TIP: Car engine oil usually comes in 5 litre or 1 litre containers. A smaller 1 litre bottle is ideal to keep in the boot for top-ups.

Comma engine oil 1 litre and 5 litre

A multi-grade engine oil is shown by two numbers separated by a ‘W’ i.e. 5W30. The ‘5’ refers to the thickness when cold and the ‘30’ is the thickness when hot. The lower the first number the thinner the engine oil is when cold, so a 5W40 is thinner than a 10W40. The higher the second number, the thicker the engine oil is when the car has warmed up.

The right engine oil for your car will depend on who it’s made by, the engine size and whether it’s petrol or diesel. Find out now by following this link: Comma Motorist Area >
Alternatively, check your car’s handbook or call a local dealership or motor spares store.


When your car is switched off, the oil sits at the bottom of the engine in what is known as the ‘sump’. When the car is running, oil gets pumped all around the engine, so you’ll need to let the oil drop back down into the sump before trying to check the oil level. Leave the car to rest for at least five minutes after you switch it off and be careful what you touch as the engine will still be very hot.

TOP TIP: Make sure the car is parked on level ground when checking engine oil level or your reading will be inaccurate.

Step-by-step guide: Click on the images to enlarge

Find engine oil dipstick
Locate dipstick:
Find the engine oil dipstick and remove it by pulling the handle, which is usually a yellow or orange hoop. On some cars it could be a black handle with ‘OIL’ or a dripping oil can marked on it.
Find MIN / MAX marks
Find Min & Max marks:
Familiarise yourself with the MIN/MAX marks on the oil dipstick but don’t try reading the level yet. Wipe the stick and push it all the way back into its tube.
Check the oil level
Check level:
Remove the oil dipstick again and this time take a look at the oil level. If it’s below the half way mark you’ll need to top up.
Replace the engine oil dipstick
Replace dipstick
Put the engine oil dipstick back once you’ve read the level.


Always top up the engine oil bit-by-bit rather than trying to get it right in one go. Recheck the level on the engine oil dipstick after you’ve added some oil, remembering to give it at least 30 seconds to drop to the bottom of the engine.

If you overfill, the excess oil makes the engine work harder and use more fuel. The increased pressure on the engine can also result in oil leaks and damage to the catalytic converter. A tiny bit over the max mark probably won’t be the end of the world, but if you do go way over, don’t risk damaging the engine by driving it. (Some of the engine oil will need to be drained out from the sump first and you’ll need the help of a breakdown service.)

TOP TIP: On most cars, the difference between the minimum and maximum marks on the engine oil dipstick is about one litre.

Step-by-step guide: Click on the images to enlarge

Find oil filler cap
Locate oil filler cap:
Find the engine oil filler cap and remove it. Have a cloth to hand to help you get a better grip on the cap as they can be tough to unscrew. (Put the cap somewhere safe where it won’t get dirty or fall inside the engine bay.)
Slowly add engine oil
Add engine oil:
Slowly add some oil and give it 30 seconds to a minute to drain to the bottom of the engine. Use a funnel to prevent spilling. (Cut the top off a clean plastic bottle to make a homemade funnel.)
Re-check oil level
Re-check oil level:
Now you’ve added some oil, recheck the level on the engine oil dipstick. If you need to, add more oil until you reach the MAX mark.
Replace oil filler cap
Replace oil filler cap:
When you’ve finished topping up, screw the oil filler cap back on. Double check the dipstick is securely in place.



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