A Beginner’s Guide to Checking Engine Oil

I learned to check engine oil at the age of seventeen, standing on a forecourt outside Crewe with my dad’s old Sierra and a small paper handkerchief I had pulled from my coat pocket. He had pulled over because the oil pressure warning had flickered for half a second on the dashboard. He showed me how to find the dipstick, how to wipe it, how to read it, and what to do about a low level. I did not appreciate it at the time. I do now, because the same five-minute habit has saved me from at least two expensive engine repairs since.

Engine oil is the single most important fluid in your car. It lubricates every moving metal surface in the engine, it carries heat away from those surfaces, it cleans, and it seals tiny gaps between moving parts. An engine running on low oil, or on oil that has been left too long, ages dramatically faster than one running on a healthy supply. The good news is that checking the oil is genuinely something anyone can do, and it does not require lifting anything except the bonnet.

What you are actually looking at

The engine has a sump at the bottom, which is essentially a metal pan that holds the oil when the engine is off. From the sump, a pump pulls oil up through a filter and around the engine while it runs. When you switch the engine off and let it sit for a few minutes, all the oil drains back down into the sump. The dipstick is a long thin rod that reaches into that sump from the top of the engine, and on the bottom of it are two marks (often labelled MIN and MAX, sometimes shown as a hatched area) that tell you whether there is enough oil.

The reading on the dipstick is only meaningful when the engine is cold and has been off for at least five or ten minutes. If you check immediately after switching off, the oil is still draining down through the engine and the reading will be misleadingly low. If you check while the engine is still hot, the oil expands slightly and may read higher than it really is.

Finding the dipstick

Open the bonnet and look for a brightly coloured handle, usually yellow, sometimes orange or red, with a small loop or T-shape. It is almost always near the front of the engine, sticking up from the engine block. If you genuinely cannot find it, the handbook will tell you where it is. A few modern cars have replaced the dipstick with an electronic oil level sensor that reads on the dashboard; if yours does that, the dashboard reading is the equivalent measurement.

The check itself

1. Park the car on level ground. A car parked on a slope will give a slanted reading.
2. Open the bonnet, find the dipstick, and pull it out. It will be coated in oil.
3. Wipe the whole length of the dipstick clean with kitchen roll or a paper towel. You are removing the oil that splashed onto it while the engine was running.
4. Push the dipstick fully back into its tube. Make sure it seats properly; it should click or stop firmly.
5. Pull it back out. Now look at the bottom. There will be a clean wet line where the oil reaches up to. This is your reading.

The line should sit between the MIN and MAX marks. Roughly two-thirds of the way up is ideal. If it is at MAX, you have plenty. If it is below MIN, you need to add oil. If it is between the two but closer to MIN, top it up at your convenience.

Reading the colour and texture

While you have the dipstick out, look at the oil itself. This is the part most people skip, and it tells you more about the engine than the level does.

• Honey-coloured to dark amber: healthy oil. This is what fresh oil looks like, gradually darkening over thousands of miles as it picks up combustion soot.
• Dark brown to black, still translucent: normal used oil, working as it should. Time for a change is approaching but not urgent.
• Opaque black, treacle-like: overdue for a change. The oil has stopped doing its job properly and the engine is wearing faster than it should.
• Milky, beige, or coffee-coloured: water has got into the oil. This is a serious problem (head gasket or coolant leak) and needs a garage straight away.
• Gritty or with visible metal flecks: internal wear. Also needs urgent professional attention.

Rub a drop between thumb and finger. It should feel slick and slightly slippery. If it feels gritty, watery, or has a strong burnt smell, the oil has either degraded or been contaminated and needs replacing before the engine is driven much further.

Topping up

If the oil is low, you need to add the correct grade. The grade is written in the handbook and usually on a small sticker under the bonnet. It will look like “5W-30” or “0W-20” or similar. Using the wrong grade can affect fuel economy and, in some modern engines, can cause genuine damage. Do not guess; check the book.

Find the oil filler cap on top of the engine, usually marked with an oil can symbol. Unscrew it. Pour oil in slowly, perhaps 250 ml at a time, then wait two minutes for it to drain down to the sump, then re-check the dipstick. Going too fast risks overfilling, which is almost as bad as running low (excess oil can be churned into foam by the crankshaft, which then cannot lubricate properly).

The capacity between MIN and MAX on most cars is about one litre. So if you are exactly at MIN, you need about a litre to reach MAX. Add half, recheck, add the rest gradually.

When to actually change the oil

Topping up replaces what has been lost. It does not refresh the oil itself. Oil should be properly changed (drained from the sump, filter replaced, new oil added) on the schedule your handbook specifies, usually every 10,000 to 20,000 miles or once a year, whichever comes first. Many drivers stretch this to two years to save money, and on a modern engine it is usually fine in the short term, but it adds wear over the life of the car.

An oil change at a garage is one of the cheapest services they offer, usually well under a hundred pounds. It is also one of the highest-value pieces of maintenance you can do, because clean oil dramatically slows the rate at which the engine wears. If money is tight and you have to skip something, do not skip the oil change.

Why some engines genuinely drink oil

A small amount of oil consumption between changes is normal in any engine. Quarter of a litre over 5,000 miles is unremarkable. More than that, and especially on a regular basis, suggests the engine is using oil, either through worn valve stem seals, worn piston rings, or a small leak somewhere. None of these are immediate disasters, but they should be investigated, because they tend to get worse.

The same logic of small, repeated care that we wrote about in our Sunday morning car routine applies here as well. A monthly oil check, taking five minutes, gives you several months of warning that an engine is starting to consume oil, which gives you time to fix the underlying issue before it becomes serious.

The habit that costs nothing

I check my engine oil on the first Sunday of every month. I am rarely surprised by what I find. The point is not that the oil is always low; it usually is not. The point is that once a month I am paying attention, and on the rare occasion when something has changed, I notice it within four weeks rather than four months. That is the whole game with engines. Catch the change early, and the engine lasts.

For a related angle, our piece on The Honest Guide to Washing Your Car Without Damaging the Paint covers a closely connected problem.