Finn:-best possible person to ask that I know is Shane Richins, hands on ,MD of Swadlincote diesels, Derby's, a longish way from you but the guy's a gem on diesels. I had a chat with him about derv fuel and he explained that modern derv has had most of the lubricants i.e. sulpher, etc, has been removed to make it "cleaner", one the worst being so called city diesel, his recomendation was " chuck some vegi oil in when you fill up," in what quantities I don't know, so it's Shane Richins tel 01283 222316, just a phone call away....callie