How often should the fuel filter be changed?

Diesel: every 20,000–30,000 miles. Petrol: most modern petrols have a sealed lifetime filter inside the tank — only changed if a fault occurs.

Here's a quick, honest answer from a working UK mechanic — what causes it, what it costs to fix, and what to do next.

Can I drain the water trap myself? — On many diesels yes — a drain plug at the bottom of the filter housing. Check the handbook.

Will dirty fuel damage the injectors? — Yes. Common rail diesel injectors cost £300–£600 each — a £100 filter change is cheap insurance.

Bob's Mechanical Repairs — independent family-run garage in Birnam, Dunkeld, Perthshire. Call 01350 727 276 or email [email protected].