The most moving part in your car

Oil is the lifeblood of our engine but we rarely give it a second thought until it drips on our drive. It stops all the moving metal parts rubbing each other up the wrong way.

Oil is the lifeblood of our engine but we rarely give it a second thought until it drips on our drive. It stops all the moving metal parts rubbing each other up the wrong way.

In scientific terms, the most important property oil has is viscosity. In cold weather it must allow the oil to flow freely to permit easy and less wearing starts. However, at higher temperatures it must retain sufficient thickness to ensure proper lubrication. Of course, we should pay a lot more attention, especially as British motorists covered 308bn miles in 2003.

More significantly, manufacturers are building cars capable of going longer between services. Although a typical service interval is every 12,000 miles, some cars running with intelligent service intervals run over 20,000 miles between oil changes or top up. No wonder so many of us have just got out of the habit of pulling the dipstick and regard the bonnet as a sealed unit. That is a big mistake.

Comma Oil is warning motorists that they run the risk of being part of an annual £300m statistic by failing to check the oil level on a regular basis. Research for the company found that poor engine maintenance accounted for one in 20 of an estimated 7.2m mechanical breakdowns in 2003, leaving motorists with an average repair bill of £1,300.

As part of its "Do You Dip?" campaign, Comma Oil is urging all motorists to check their oil regularly and before they head out on a long journey. "Checking oil is still relatively simple," explains Mike Bewsey, a spokesman for Comma Oil.

"Motorists who rely on the oil light to alert them to the need to refill, or wait for the vehicle to be serviced are risking engine damage, possible breakdown and as well as an engine replacement." How much oil an engine uses is dependent on a variety of factors, including cold starts, ambient temperature and distance travelled. As a result, the need to regularly check oil levels, and more importantly, top-up, in between annual garage visits is even greater. It is estimated that, at any one time, one in four cars on the road need a top-up.

Oil firms are countering the effects by developing oils specifically for longer service intervals. Comma's Eurolite 10w-40 and Eurodiesel 15w-40 oils are designed to improve operation in extremes of heat and cold. The company has also introduced an oil for Volkswagen and Audi engines that run on the long life service regime.

Ten-minute trips to the shops can consume as much oil as a high-mile journey and also causes the most damage to your engine. A car that only does short journeys can suffer serious mechanical wear as the engine internals effectively shrink. That is because the metal is being removed by chemicals or mechanical action so bearings, cams, pistons and cylinders are more prone to this kind of wear. Remarkably, 90 per cent of engine wear occurs during the first 10 seconds of the start, roughly equivalent to the wear inflicted on the engine of a car that is taken for a 500-mile run.

According to the experts, you should check your oil level at least every 500 miles or once a week and park on level ground, where possible. I'll assume you know what the dipstick looks like. On older cars it will be found in the middle of the engine, increasingly it has a yellow cap. Take it out, wipe it and feed it in again. Take it out and read it. This is crucial, as some oil will creep along the gauge when the engine is shut off, so the first measure will be faulty.

On most vehicles there are two marks on the gauge. The oil level must be between the upper and lower marking. You will find in your owner's manual how much oil you must add for topping up. Generally, this will be between 0.5- and 1-litre. Don't hurry, just add a little at time and return after five to 10 minutes to check the level.

You must consult the manual or the manufacturer for the definitive procedure because, although the engine should be switched off for the majority of cars, there are exceptions such as the Porsche 911 and some can have more marks on the dipstick, such as the Land Rover. Wipe around the cap so dirt doesn't get into the engine and never overfill an engine. or seals may start to leak and foaming of the oil occurs which can push oil into other areas.

Checking oil is a priority, but which oil is right for your car? You might want to use Shell Helix because Michael Schumacher does in his Ferrari, but whatever you choose make sure that it is a decent brand. Avoid cheap stuff that may be sold on price rather than performance.

The latest synthetic oils have additives to help keep an engine running smoothly. But a modern oil may be inappropriate for an older car. Modern engines are built to tight tolerances and take less oil so it reaches the right temperature quickly. Today's premium synthetic oils are too thin and full of detergents for older engines, which is why Penrite makes more robust oils specifically for classics.

Oil isn't just honey coloured and slimy, it keeps your car's engine moving. Once it turns black, it's overdue for a change.

motoring@independent.co.uk