How often should you change the engine oil?

Which is more important – the quality of engine oil you use or how often you change it?  Many readers

Both matter, but generally, the very high quality of almost all modern engine oils sold in reputable station forecourts puts a greater emphasis on change intervals.

Whatever oil you choose – as long as it meets the “grade and weight” standard set by the engine manufacturer – will give adequate protection and performance. 

It will do no harm.  A more expensive higher grade (including the most advanced synthetic oils) might, or might not, do any “extra” good. 

Every type, grade and weight of oil degrades with use and needs to be periodically changed to maintain its full function. There is no absolute answer to how long it lasts because there are so many variables…in engine design, age, condition, and general usage (journey patterns, driving style and the road, traffic and climate environments).

The oil itself is not the only item of maintenance discipline. Its efficiency and longevity also directly depend on the quality and condition of the oil filter (direct) and variables in the cooling system, fuel injection and ignition timing (indirect).   

If the filter is fouled or faulty, it will accelerate degradation whether the oil you put in costs you Sh150 or Sh1,500 per litre.   There is plenty of scope for false economies or wasted investments in this area. 

All these variations can halve or double the life of an engine.

So, while it is impossible to say to every reader “this is exactly how often you should change your oil, no matter what”, I can offer two suggestions:

For a very wide range of “ordinary” cars used in a wide range of “ordinary” conditions, the oil grade and weight specified by the engine manufacturer will maintain its adequate level of protection and performance for about 5,000 km. 

On average!  So use that figure as your benchmark unless there are compelling reasons to do otherwise. There is no good reason to wait until your oil is sub-standard before changing it. 

In out-of-the-ordinary circumstances, the original oil quality might decline sooner or last longer, and the change interval could be adjusted.

If you assess your motoring to be “extra-ordinary” (in either direction, in either general or special circumstances), then adjust your change intervals accordingly.

In making that decision, bear in mind that if you change the oil more often than necessary it will do no harm. The new stuff will always be in better condition than the used stuff – the oil does not improve in any way whatsoever from the moment you drive it off the service pit.   

And if you don’t change the oil often enough, don’t kid yourself that you will be saving money. In the long run, motoring with degraded oil will affect performance and fuel economy and increase engine wear… often by much more than you would have spent on an oil change… with a good filter.

So make 5,000 km your benchmark, and only vary it for “good” reasons.

Meanwhile, there is a technical difference between the best and the rest, and if you can readily afford top-of-the-range synthetics, they are well worth considering.

Not because they will revolutionise your motoring experience (in “ordinary” cars any benefits will be marginal), but because over time they will maximise (by some degree) the durability and reliability of your engine.  

And if, for any reason at any time your engine is starved of oil, lubricants designed for very high performance might reduce the amount of damage that is done before you find out.

In safety-belt terms, cheap oils are lap straps.  Recommended qualities and grades have a diagonal shoulder strap, too. And high-performance oils are double harnessed with a crotch strap. No one has invented the engine oil equivalent of an airbag. Yet.

And, as mentioned in this column before, if your engine ever seriously overheats, when you have the cooling system fixed, change the engine oil, too.