sustainablog: Lubing Your Engine with Coke Bottles...

May be a possibility in the future thanks to "...a new process for converting waste plastic into lubricating oil for engines." Mike at Green Car Congress notes that such a product would provide several environmental benefits:

First, a more stable synthetic oil (an oil with high paraffinicity and, therefore, high Viscosity Index (VI, signifying high stability to change in viscosity over a wide temperature range) and low viscosity) will extend the interval between oil drains. That in turn reduces the amount of used oil requiring disposal. According to the EPA, some 200 million gallons each year are dumped into the environment.

The other benefit of a low-viscosity oil is reduced engine friction and thereby improved fuel economy.

Second is the obvious benefit in being able to recycle a portion of the ever increasing stream of waste plastics. Plastics represent 11 wt% of municipal solid waste today, up from less than 5 wt% in 2001.