It's no more expensive to fill up when half full, unless visits to the fuel pump make life difficult operational wise. Do diesel stabling points not have fuel facilities.
Do diesel locos run on normal diesel fuel, or do they use red diesel. I bet their price per litre is a hell of a lot less than we pay, bloody tax.
Whenever I see photos of steam locos there always seems to be a big enough pile of coal, or is it just me ?