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Hi Jack, I have recently bought a used BMW X3 2litre diesel. More recently I've become aware of potential problems regarding poor quality fuel and wonder if it affects all motors or just some. I understand the problem to be water in the fuel causing a "bug" and wonder if I should change my fuel filter more regularly. Your thoughts and any advice would be welcome.

Malcolm

The issue isn't poor quality fuel as such but rather diesel contaminated with water. Water contamination has always been a risk with any mineral fuel, but modern common-rail diesel engines are very intolerant to the presence of water, or more specifically 'diesel bug', which may form after the water has been sitting for some time. This very rarely happens with services stations, but some people have been caught using diesel from farm tanks that don't have the strict maintenance regime or frequent turnover of service stations. Water can also form in your own car tank, particularly from condenstation.

As a tip, its best to try and keep the tank topped up, particularly if you don't use it often, or if you park it outside overnight, to minimise the risk of condensation forming. If you are concerned about fuel quality, try to buy from (the same) large, modern service station with high turnover, and keep your receipts. As for replacing the filter, this is very important to minimise damage to the fuel system so you must stick to the recommended service intervals.