All this talk about RUCs and diesel led me to do some more research into a side-interest I've had of fueling a vehicle on used vegetable oil - think takeaways on wheels.

Yes, there is a small movement in the United States of America in particular to partially convert vehicles to run on both diesel and vegetable oil, but I am only aware of a few light vehicles being run on it in New Zealand.

It's nothing new, Diesel himself was writing about using vegetable oil as far back as 1912, when the French government suggested running an engine on peanut oil. 

I do wonder though whether it would induce irrepressible cravings for those good old Kiwi greasies!?  You could perhaps scent the oil and ooze aromas of chocolate, liquorice, jellybeans, or pineapple chunks instead as you travelled through the city and countryside - a confectioner's marketing dream.

Back to fundamentals...

A conversion involves fitting a secondary tank (although some installations swap the tanks over thereby using the main tank for the oil and a smaller secondary tank for the 'back-up diesel'), filling entrance, hoses, heating elements, and a few other bits and pieces.  

When you start your vehicle you start it on diesel until the oil in the tank is heated enough, press a button to switch it over, and hey presto you are cruising on canola or whatever your preference is.  When you have almost arrived at your destination you switch back to diesel for a bit to flush out the lines.

There is the extra effort required in hunting and gathering your ingredients - approaching a restaurant or takeaways that would otherwise pay to have their waste oil removed from their premises.  Transferring that into your holding container - this can be a messy business; then into your fuel tank after filtering.  [Sometimes you can skip the middle step and put the oil into the vehicle tank but it still needs to go through a process of filtering at some point - it depends on how your system is set up.]

Conversion of a light vehicle (under 3500kg) requires an inspection by a Low Vehicle Volume Technician.  These are usually people who look at sports cars, cars that have been lowered, or had improvements to make them more efficient over and above your regular off-the-factory-line automobile.  The fees start at $500 and go up from there.  After inspection they order a metal plate be made and fitted to your vehicle that a WOF/COF agent will need to see each time your vehicle needs it's regular road-worthiness testing.

Low Vehicle Volume Technical Association

NZTA have information on their website for light vehicles about CNG and LPG conversion but no other fuel sources; so I guess it comes down to a case-by-case basis and the individual discretion of the technician 

As far as converting heavy vehicles (anything over 3500kg) is concerned NZTA's preliminary advice is that a change to the fuel system would need to be inspected by a Heavy Vehicle Certifying Engineer (pdf list).  

Different certifiers are allowed to inspect subject to their different areas of expertise.  These areas are the codes in the last column of that table which are explained on the Heavy Vehicle Engineers website.  None of which are specifically 'fuel systems'.  The closest one gets is HVEC being engine transmission.

The difference in this process is that you are best to contact the certifier prior to starting any work as they will need to inspect before, during and after a change has been made.  Then they will issue a LT400 paper certificate (instead of the metal plate mentioned above for light vehicles) which you lodge with any heavy vehicle testing station (CoF agent) for loading onto the NZTA Landata database.  

So far it doesn't look as if there are any widely-publicised guidelines for heavy transport fuel conversions.  Has one even been done in New Zealand?  You would definitely want to know that you had a chance to be approved prior to installation as you don't want to go to all the cost, time and effort to have it declined.  Watch this space as we update the post with further information as it comes to hand.

One of the overseas veggie fuel system suppliers that we contacted, Golden Fuel Systems recommended that overseas customers (given the specifications we were enquiring about) purchase a tankless system as this would be less expensive to freight, and source a locally-made tank.  The question would be finding a knowledgeable installer.

It seems that for about NZ$4000, plus installation, and certification ($500+) you could convert your vehicle to run on veggie grease.

The real question is 'how easy would it be to source vegetable oil around NZ to fuel the vehicle after conversion?' and 'would getting it remain free?'.