not important this time of year bu they recon palm oil sets hard in cold weather!
we have a fridge with a digital temp dispaly and i actualy tried to see which oils set at what temps, it might be worth doing and making a note ready for next winter, its not that far away!
a quick addition, i agree with HB the risk 'v' savongs eqation makes it unrealistic to me. paying around a £1 for veg oil or £1.16 for diesel (the price i paid at asda the other day) you would have to use a hell of a lot to pay for even minor issues.
for example it is understood that using veg oil dilutes sump oil, so if you change it twice as often 2 gallons of decent oil, plus a filter, plus time and effort, shall we assume £40-£60?
you have to save a lot of 16p's to pay for it!
and if you can claim any tax back on fuel use (i doubt you can on veg oil as it is zero vat rated) it definately aint worth it!