This happened to me a couple of weeks ago. I parked in the shopping mall parking lot and couldn't help but notice a strong smell of burnt oil. I mean, burnt cooking oil, like when you are going to fry something, put the pan on the stove and forget about it an the oil gets too hot and burns.
A few steps closer to the mall entrance and I see that rastafari-haired hippie on his VW van, you know the kind, the typical sixties WV hippie van. That's where the smell was coming from.
I've heard many times about farmers using used kitchen oil in their tractors. That was the first time I saw it with my very eyes -and smelled with my very nostrils-.
I don't think I'll give it a try on my Audi though.... :-) neither oil nor pee.