firstly DON'T use thinners, it'll eat the seals in the dizzy pump...
you CAN you WVO, BUT... WVO is acidic, and its full of crap which your engine won't like. and, during winter it turns to sludge, and your van won't start.
i bought a volvo 760tdi, it was run on WVO from dirty dans burger vans... OK, i got the volvo cheap, but it cost nearly 400 quid to sort it out. (reconned distributor pump and exhaust system) after that it ran for 4yrs without a hiccup..;
if you want to mix WVO then use diesel to do it! we use 1gallon of diesel to 10g of WVO...the colder it gets, the more diesel we add.
oh, and change the fuel filer EVERY OTHER MONTH, they clog really easy. youre saving a fortune on fuel, buy a few more filters.
type biodiesel or WVO into google