Changing engine oil can be an enjoyable project

Changing the engine oil is one of the nicest jobs that the home mechanic can do.

Changing the engine oil is one of the nicest jobs that the home mechanic can do.

It has to be done roughly every 12000km, but the interval depends on many factors.

Under adverse conditions, such as when a car is only used for short trips, where the oil never gets hot enough to drive off contaminants, the oil should be changed say, every 7000km. This also applies to a worn engine which has heavy contamination past the rings.

The same applies to diesel engines, which tend to produce more soot and acidic blow-by, and turbo- charged engines, in which the oil can get extremely hot. On the other hand, for an engine in tip-top condition, which sees a fair amount of freeway driving, and which runs on one of the high-quality, long-life oils now available, the change interval can safely be extended to 20000km.

Synthetic oils, in particular, are resistant to the effects of heat, and are not quickly degraded by the shearing action of closely rubbing surfaces.

This has allowed the drain intervals on new engines to be extended despite the fact that today's engines run hotter than ever.

When it comes to choosing the best oil for your engine, the only reliable guideline is the technical information printed on the container. If the following details don't appear there, walk away from that oil:

l The viscosity range of the oil, for example SAE 10W-40 or 20W-50. Keep in mind what your vehicle handbook recommends.

l The specifications that the oil meets, both from the American Petroleum Institute (API) and its European counterpart, ACEA. API has an S rating for petrol engines (S for spark) and a C rating for diesel engines (C for compression-ignition). Look for SL or SM and CH4 or CI4 on an up-to-date oil. ACEA follows a different rating system. In their case A3/B3 or A5/B5 or C3 indicate the better quality oils.

l The approvals that the oil has gained from vehicle makers. Significant ones at present are VW 504, 506 or 507; MB 229.3 or 229.5; BMW LL01 or LL04. Note that a statement "Approved by XYZ", but with no qualification code carries no weight.

For vehicles older than 10 years, it is best to use a slightly thicker multigrade oil, and to drain the oil more frequently than on a newer engine.

Ideally, drain the oil when the engine has just come in from a brisk run. The hot oil will flow easily to carry all sediments and sludge with it before these can settle in the sump.

Allow the oil to drain completely while you have a cup of coffee. Then replace the plug and refill the engine with the correct amount of oil, as given in the handbook. Do not overfill!