As you don't specify exactly which 1.8 (B4184SM, B4184S or B4184S2) or how you use it it's difficult to say. If thrashed up and down motorways (which I did far too often last year) mine (B4184S2) uses a litre about every 3-4k, driven more sensibly it's about a litre every 7-8k. Hope this helps..