Devices of this type include: Slick 50, Duralube

There are plenty of oil additives on the market that claim to reduce engine friction and so save fuel. Often they also claim to reduce wear, and sometimes support this with tests showing engines running without any oil. I have included some information on these products here for completeness, although they are not technically fuel saving "devices".

Now, my field of expertise is combustion, not friction, so I can't say anything definitive about these additives. A couple of people who apparently do know about them are Chris Longhurst and The Skeptic's Dictionary. Both of these sites - and there are others, if you care to look - suggest very strongly that these oil additives are less effective than the makers claim.

Many people have observed that a modern engine will actually run for a surprisingly long time without oil anyway, so the demonstrations of engines treated with Product X and then drained of oil are less conclusive than you might think. The fact that the makers of such products are regularly prosecuted for false advertising is cause for scepticism. Finally, there is the standard argument over why the oil companies with their multi-billion dollar research budgets have not found this miracle product while some fairly small outfit has.

Having said that, reducing friction is undoubtedly a powerful tool in reducing fuel consumption, and this has been a major factor in driving the "typical" oil from 20W50 to 10W40 or even 0W30. Providing the manufacturer has approved its use in your car, switching to one of these lower-viscosity oils will give a small but significant fuel economy benefit. Adding a "friction reducing" additive as well seems unlikely to be cost-effective.

My general advice on oils would be: use a high-quality synthetic or semi-synthetic oil from a reputable manufacturer and you won't go far wrong. A good fully-synthetic oil should offer just as much protection as the essentially random combination of cheap oil and an aftermarket additive (and may well be cheaper), and gives the confidence that the "mix" has been fully tested by the manufacturers. If you use your car in "extreme" conditions (either lots of high load/high speed, or lots of cold town driving) then it is probably worth changing the oil more often than the handbook recommends.

However, some engines are especially demanding in their oil requirements (for example VW's PD diesels and extended service interval engines) and in this case you must use an oil specifically approved by the manufacturer. In some cases this may mean actually buying the oil from your local dealer, which is expensive but does give you 100% confidence that the oil has been tested with your specific engine.

Oil change intervals

In Europe, it is common practice to change engine oil after 10,000 miles, or in some cases as much as 15,000. Strangely, in the US it seems normal to change at 3,000 miles (even when a much longer interval is specified by the manufacturer). Of course there are differences between Europe and the US - for example extremes of climate, and differences in fuel type - and it never does any harm to change the oil more frequently. But potentially you can save a lot of oil, and a fair bit of money, by following the manufacturer's recommended change intervals rather than always changing every 3,000 miles. In particular, if most of your driving is steady cruising down the freeway on long journeys, you are putting a lot less "stress" on the oil and under these circumstances "every 3,000" seems much too often.

The usual warning applies, though: check your car's handbook carefully, and don't exceed the recommended change interval. And if you are going for long service intervals, it's especially important to use a good-quality oil.

A useful guide to engines oils in general is the Engine Oil Bible; indeed the other Car Bibles are worth a look, although not of particular relevance to this site.

Please also read the general comments on fuel "saving" devices, if you have not done so already.

If you found this page helpful, you may like to support my work. If you think I have made a mistake, or am talking complete nonsense, please take a moment to read the Response to Critics before saying so in public (on discussion Forums and the like).