Hi Alex,
Actually, no, the vegetable-oil addition does not affect the warranty. I have been running my car on the fuel modification since 2009, which is noted in my service book. When my con-rod started giving trouble at the beginning of the month, I left the vehicle with Nissan. They simply disconnected my new pipework, removed the engine, and sent a copy of my service book to Nissan UK along with all other relevant stuff. Contrary to popular belief, vegetable oil, when used in conjunction with an authentic high-quality conversion - such as the Elsbett one - enhances lubrication and reduces wear; you also get better performance since vegetable oil captures more energy than equivalent volumes of diesel.
Anyhow, after a couple of days, Nissan agreed to provide me with a brand new engine (ÂŁ4500+ parts/I paid the labour of ÂŁ1050), and they simply reconnected my veg oil kit. You simply can't do better: a new engine that runs superbly on fuel more than 40p a litre cheaper! Unfortunately, living in N Ireland, I have no local suppliers of reconditioned SVO, otherwise my savings would be huge.
All best,
Jonathan