Nowadays with these common rail diesels it's quite rare to find people running their diesels on straight cooking oil in fact I've not been behind one for a few years. I used to frequently be behind a car that stunk like an overheated chip pan.
I had a Citroën xantia that ran on cooking oil, used to buy it from Makro, around 7 years ago. In the winter I'd put 40 oil to 60 diesel in it.
Surprisingly it is possible to run a diesel car on vegetable oil, in fact some of the very old non hdi engines can run on pure vegetable oil. Back in 2000 when we had the fuel protesters stopping the wagons leaving the refineries and there was massive queues for the small amount of fuel available I ran my Fiesta on vegi oil for 3 weeks bought by the trolley load from Aldi.
First bite of the day (lol)
I'm sure I also read somewhere contradictory to people's beliefs lard and beef dripping is in some ways better for you because it contains less of the dodgy unhealthy fats than veg oil does.