Poor fuel economy after service

My Vauxhall Zafira 1.7 diesel (13 reg) used to do about 45 miles to the gallon around town but after my last service it does only 38 miles to the gallon. Can you tell me why this has happened?

It's winter and it's colder, so the engine remaining on heavier mixture for longer will be partly responsible. Try switching to better fuel, such as Shell V-Power Nitro Plus diesel.

Answered by Honest John on 6 January 2016