I've been starting a Nissan 2.7 tdi every morning 'iced up' & down to minus 7C with no problems at all ie 'first button'with neat biodeisel with no additives at all. I would like to ask all you cleaver folks out there about storage of the finished fuel. I am now storing in the underground tank (unfortunately mild steel)ready for spring/summer use. Does any one know if the fuel stores any better if a 'cap' of readily available CO2 is put on it instead of air - would it be beneficial ??????

You're taking a gamble running at low temps without additives of some sort. You'll get away with it for a while with good rapeseed or soya wvo but sooner or later your pump, filter and hoses will block solid. Even a little petrol mixed in does a reasonable job (5%).

I dont know much about oxidation rates but if youre going to have a CO2 'atmosphere' it'll have to be airtight. You'd have to drive off any dissolved air which might be present too.