How to check your engine oil

Engine oil is one of the cheapest things to keep on top of and one of the most expensive to ignore. It lubricates hundreds of fast moving metal parts, carries heat away, and helps keep the inside of the engine clean. Let the level drop too far and those parts start to wear against each other, which can lead to a repair bill many times the price of a bottle of oil. The check itself takes about five minutes and needs nothing more than a rag.

This guide covers why oil matters, exactly how to read the dipstick, what the level and colour can tell you, how often to check, and how to top up without overdoing it.

Why oil matters

As the engine runs, oil is pumped around to coat every moving surface in a thin protective film. That film stops metal grinding on metal, reduces friction so the engine runs cooler, and picks up tiny particles and carries them to the filter. Over time the oil gets dirty and breaks down, which is why it is replaced at each service.

The problem with a low level is that it is invisible from the driving seat until it is serious. Many cars only light a warning lamp once the pressure has already dropped, by which point damage may be under way. A regular manual check is the reliable way to catch a slow leak or a thirsty engine early.

The dipstick method, step by step

Most petrol and diesel cars have a dipstick, usually with a brightly coloured loop handle near the top of the engine. Some newer cars have done away with it in favour of an electronic reading on the dashboard, so check your handbook if you cannot find one. If your car has a physical dipstick, here is how to use it.

1. Park on level ground. If the car is on a slope the oil pools to one side and the reading will be wrong. Flat and level is essential.

2. Switch the engine off and let it cool. Oil is best checked cold. A warm engine is acceptable, but wait at least ten minutes after switching off so the oil drains back into the sump and settles. This also avoids the risk of burning yourself on hot parts.

3. Pull the dipstick out and wipe it clean. The first reading is unreliable because oil is splashed all up the stick while the engine runs. Wipe it completely clean with a lint free rag or kitchen roll.

4. Reinsert it fully, then remove it again. Push the clean dipstick all the way back into its tube, pause for a second, then draw it out steadily. Now the oil film shows the true level.

5. Read the level. Look at the marks near the tip. There will be a minimum and a maximum, sometimes shown as MIN and MAX, LOW and HIGH, or a pair of notches or holes. The oil should sit somewhere between the two, ideally nearer the top mark.

What the level and colour tell you

If the film sits between the marks, you are fine and no action is needed. If it is at or below the minimum, the engine is low on oil and you should top it up before driving far. The gap between minimum and maximum usually represents a meaningful amount of oil, often around a litre, so even a reading just under the minimum means a fair bit has gone.

Colour is a softer clue. Fresh oil is amber or light brown, and it darkens naturally as it does its job, so dark oil on its own is not a cause for alarm. What is worth attention is oil that looks milky or has a mayonnaise like texture, which can suggest coolant is mixing in, or oil that feels gritty or smells strongly burnt. Any of those is a reason to have a garage investigate rather than simply topping up.

It is also worth glancing at where the car has been parked. Fresh oil spots on the driveway point to a leak that is worth getting looked at before the level drops again.

How often to check

Getting into the routine of checking every few weeks is a sensible target, and always check before a long journey. Cars with higher mileage, or any engine known to use a little oil between services, deserve a closer eye. Keeping the level right between services is one of the simplest ways to look after an engine and protect its value.

Topping up without overfilling

Use the oil grade specified in your handbook, as the wrong viscosity can affect how well the engine is protected. When you top up, add a small amount at a time, wait a moment for it to drain down, then recheck with the dipstick. It is far easier to add a little more than to remove excess.

Overfilling is a genuine problem, not just wasted oil. Too much oil can be churned into foam by the moving parts, which reduces lubrication, and the extra pressure can push oil past seals and cause leaks. Aim to bring the level up towards the maximum mark, never above it. If you go over, the excess should be drained off rather than left in.

When to see a professional

Top up small drops yourself, but book the car in if the level keeps falling, you find milky or gritty oil, the oil warning light comes on, or you spot leaks under the car. These point to something an oil top up will not fix. A full oil and filter change is part of routine servicing, so it is worth knowing how often you should service your car and roughly what a car service costs so nothing creeps up on you. If in doubt, a quick check by a garage is money well spent.