I an an owner of a Tino 1.8 petrol and it has recently started using high amount of petrol, it was doing about 36 miles per gallon but has dropped to about 20 over the last year. It was at 67000 miles when bought and is now at 126000, anyone know what might be the cause, it was serviced regularly and when we purchased it our mechanic looked it over and said it was in tip top condition?