Why choosing the right oil is so vital to car engines

By DPA | 26 May 2020

BERLIN: Nobody wants their car engine to seize up on the road, least of all because that can get expensive — and so you need to use oil, which cleans the motor and protects it from corrosion.

But too little oil or oil that's too old won't have the desired effect and not all oil is good oil. So what should motorists know about it?

"You should check your oil level regularly, ideally once a month," says Soeren Heinze from the car club Auto Club Europa (ACE).

Unless it says otherwise in the vehicle's manual, it's best to carry the check out after it's driven at least 10 to 15 kilometres and five minutes after you've turned off the motor.

But it's not just about checking the level, it's also about the oil itself. "If the oil is cloudy or even black and smells burnt you definitely need to go to a garage, but you also need to do that if you know the last time you changed the oil was a while ago," says Heinze.

As for what oil you use, what's most important is to look at the manufacturer's guidelines, which you can find in the manual and which you can compare with the label on the oil container.

There are mono grade oils which are only used either in summer or winter and multigrade oils which can be used all year round.

The viscosity of the oil, which is determined by its SAE grade, is an important factor in choosing the right oil.

The number before the "W" indicates the low-temperature viscosity: the lower the number, the runnier the oil and the more suitable it is for winter temperatures. A higher number behind the "W" indicates it is thicker at high temperatures and so more suitable for the summer.

To make the choice more difficult, most oil manufacturers offer different price categories. So-called long-life oils supposedly last longer, are usually thinner and as high-lubricity oils ensure significantly lower petrol consumption.

They maintain viscosity at lower temperatures and are usually graded between SAE 0W-30 and SAE 0W-40. The most commonly used is 5W-30, making oil changes necessary every 30,000km or every two years. A heads-up: these oils cannot be mixed with others.

"In general it's very important to keep to the classification that the manufacturer prescribes for your car," warns Heinze. "The wrong one, or mixing them, can cause a lot of damage.

Oil manufacturer Liqui Moly says the same thing. "Lubricant has been a custom-made part for years now," its marketing director Peter Baumann says. "You can't put any lubricant in any vehicle, it's technically impossible or at least very risky."

Oils are usually offered in different price categories, sometimes with the selling point that they can save on petrol. However that can only be tested in the laboratory — there are too many other factors at play on the road.

Baumann says the condition of the vehicle and what it's used for as well as the driver's skills are what are decisive. "A factory-new or newly broken in car behaves quite differently to a car that's already been driven for 20 years. To give a generalised figure would be ridiculous."

What's more important than the oil could be your own foot on the gas pedal: "We can save a lot more petrol by paying attention to our own driving, for example by looking ahead more while we're driving," says Alexander Klein of Germany's federal association of medium-sized mineral oil companies.