Oh.

David Lawlor writes:

The Green Van man filling up this morning at Tesco station, Dundrum [Co Dublin].

 

UPDATE: When running a diesel engine on vegetable oil, you first need to heat the oil to a combustible temperature. This is done by starting the engine on diesel. Once the engine is running on diesel, lines from the engine’s cooling system provide heat to warm the oil. The driver can then switch fuel lines to use the oil. Unfortunately, this requires filling the diesel tank every now and again. (from commenter Condor D, see below)