All cheap and good on the car front
unless you get rumbled by the police who do occasionally pick up on this wheeze in a regular tank-dipping exercise, then you may get knackered for fuel excise duty avoidance...

EDIT oops, apparently the law has changed and you can do it for the first 2500 litres per year so long as you keep a record/receipts etc. but not all diesels will take straight vegetable oil, some require modifications, some need a preheater before the fuel pump but it's also more viscous in the cold so best use it as a mix...
( Rotating Wobbly Hat That's not a banana. THIS is a banana., Fri 11 Nov 2011, 11:18, 1 reply)

I have indeed been "dipped" by the nice people from HM customs.
Simply keeping Tescos receipts and knowing about the 2500 litre allowance helps (2500 liters = 21000 miles, I only do 4000) as for cold weather I just bung 5% petrol in the tank.
The old Merc engine doesnt need a preheater but I did fit a larger inline fuel filter.
(Orkstomper, Fri 11 Nov 2011, 11:46, closed)

Top hole then :-)
proceed.
( Rotating Wobbly Hat That's not a banana. THIS is a banana., Fri 11 Nov 2011, 11:59, closed)

If you're getting the oil for free
it would still save you money if you had to pay the fuel duty wouldn't it?
( thistle, Fri 11 Nov 2011, 21:28, closed)