Engine oil is one of the most important parts of any car. But because it’s out of sight it’s out of mind. And that makes it all too easy to neglect. It’s needed to lubricate the engine, help collect and capture microscopic particles of debris and keep things cool. As oil ages, it loses its ability to do these things, which is why it’s vital drivers check their engine oil and have it changed at recommended intervals.
In extreme cases, having too little oil or old oil in the car could cause a catastrophic engine failure. So it’s alarming that a survey conducted by oil manufacturer Mobil 1, revealed that three quarters of British drivers don’t know how to check their car’s oil. And half of those questioned weren’t even sure why oil was used in their car’s engine.
What does engine oil do?
Every engine is packed with fixed and moving metal parts. As these operate together, oil is needed to form a thin, protective barrier. This lubricates the parts, helps manage heat caused by friction and minimises gradual wear and tear.
How often should engine oil be checked?
Experts recommend drivers check their car’s engine oil level once a week. Nick Reid of Green Flag said: “Ideally, we’d recommend drivers check their oil weekly. If you can’t manage that, at least do it monthly. Most cars have an oil warning light that should glow red if the oil level gets too low. However, if you leave it until the red light comes on, the engine may have suffered seriously.”
How to check engine oil with a dipstick
A dipstick does what it says on the tin. It’s a stick that you dip into the engine’s oil reservoir, then pull out again to see whether or not there’s enough oil.
If you haven’t done this before, the best time is roughly five or ten minutes after switching off the engine with the car parked on level ground.
Read the vehicle handbook first and grab a couple of pieces of paper towel. Then open the bonnet, secure it with the bonnet stay, and locate the dipstick. Use one piece of kitchen towel to grasp and pull out the dipstick, and the other to wipe it clean at the end. Re-insert the dipstick, then withdraw and see where the oil sits in relation to the ‘maximum’ and ‘minimum’ levels marked on the stick.
How to check engine oil with a digital display
Modern cars sometimes use a digital display to tell the driver how much oil is in the engine. This can be checked by reading the vehicle handbook and following the instructions for selecting the correct menu on the dashboard’s digital display.
If you think the engine needs a top-up of oil, the vehicle handbook will detail the type of oil required. Alternatively, oil makers offer easy-to-use search tools on their websites, or speak with the vehicle manufacturer’s customer service department.
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It’s important to check this: different cars and engines use different grades of oil, offering protection across a varied range of temperatures. Only add very small, 100ml amounts, before checking the dipstick or digital level again. Overfilling can cause as much damage as letting oil run out.
How often should oil be replaced in a car?
The car manufacturer will have set a service schedule for your particular make and model of car. The most common oil change requirement is once a year or every 10,000 miles (whichever arrives soonest). However, some cars are able to go for up to two years between services and oil changes. When it is changed, the old filter is removed and the oil is drained out of the car, before a new filter and oil are added. Watch the Fifth Gear film to find out whether old oil affects a car’s performance.
What are the obvious signs of old engine oil?
New oil is almost amber in its appearance. Old engine oil turns to a dark brown shade over time. This is because oxidation takes place and minute particles of debris build up. You’ll be able to notice the difference in colour on the dipstick, and also by lifting the engine’s oil cap, which is where any top-up lubricant is poured.
James is a motoring journalist and former magazine editor at BBC Top Gear and Auto Express. He has scooped, reported on and reviewed most new cars of the past 20 years, and currently contributes to the Driving section of The Sunday Times.