i have " mercedes" van here at present which has a deriviative Mercedes Diesel ( normally a OM602 it's a SSang Yong OM611) i haven't got it running yet because i'm still trying to find a new head,but i fiound this site
Ssangyong Owners Club
where they have been running their Mercedes diesels on cooking oil bought straight from the supermarket. That's right ! ,straight from the check out and into the fuel tank..We'll beat them yet! ha ha