Choosing car oil

Choosing car oil is a very responsible undertaking. Any car, be it a Hummer, a Mercedes or a Ford, is fairly demanding about this lubricant. You can't afford to get the choice wrong, since doing so will cause serious damage to your vehicle's condition. And conversely, the right product can push a major overhaul of your car off into the indefinite future.

In fairness, it has to be said that new-car owners don't face this problem of choosing a lubricant at all. If the car's under warranty, the oil is changed at the dealership, following all the maker's recommendations to the letter. It's a different matter once the warranty on a Cadillac, Opel or Ford has run out. That's where every car owner goes their own way. Some carry on the fine tradition started at the service centre. Others switch to a different brand of engine oil.

But remember that by blindly following the carmaker's instructions, you're quite likely caring more about the environment than about your own vehicle. The thing is, today's global trend is that saving petrol and being kind to the environment are priorities for carmakers. That's why makers usually recommend low-viscosity engine oils. Oils like these cut fuel consumption, but unfortunately don't do the engine's condition much good.

In Europe, this state of affairs bothers no one: it isn't customary there to run a car for more than ten years. If you share this "European" outlook, you can happily use the oil recommended by the carmaker.

For everyone else, my advice is to choose your lubricant carefully, taking a whole range of different characteristics into account.

So, first, remember that your Chevrolet Cruze, Opel Corsa or Ford Focus deserves better. So don't skimp on its upkeep. When buying oil, check that its quality is certified by the API (American Petroleum Institute).

Second, you need to correctly pick the oil's viscosity grade. It's set by SAE and comes in several forms. As a rule, practically every oil on the market today is an all-season type. But that doesn't mean at all that they're all equally suited to different weather conditions. So, on an engine oil's packaging you'll see an SAE marking made up of two parts. The first is denoted by the letter W together with some numeric figure. By correctly decoding that figure, you can work out its cold-weather pumpability.

There's a fairly rough-and-ready but workable way to work out the temperature an oil is meant for (this refers to the cold-start temperature). To do this, you subtract 35 from the first number in the marking. For example, the winter viscosity grade is marked as 0W. Subtract 35 from 0 and you get -35 degrees. This means the oil can be used in the harshest frosts (down to -35 degrees). If the packaging says 15W, some simple arithmetic will tell you it isn't meant for use below -20 degrees Celsius (15-35=-20).

As for the summer characteristic of engine oil (marked on the packaging by the second number), things are simpler here. As a rule, the most common viscosity figure is 40. That's the most widespread grade. There are, of course, also fuel-saving oils with a lower figure, but such oils should only be used strictly in line with the carmaker's requirements.