First point :-
you smell like a chippie if you recycle oil from a chippie --- its long and complicated (plenty of sites tell you how) and if only a very, very small error in filtering --- it will clog the injectors fast.
As a bynote :- if you use oil from the local chinese, you smell like a chinese chippy --- I tried it.
Police in some areas stop anyone with a "smell" as it must be illegal ---- in fact most recyclers use a recognised "recipe" and pay (used to pay) the fuel duty at 28 or 43p per litre.
IF YOU USE NEW OIL - THERE IS NO SMELL it is "cleaner" smelling than pure diesel.
Second Point:-
I use Oil from the supermarket shelf ---- no processing --- no filtering --- as it comes.
higher priced oil is no improvement ..............
Sunflower oil is the highest cetane and therefore best.
Rapeseed (marked "veg oil" or "canola") is great, better lubricant but slightly lower cetane.
Olive Oil, Palm oil, grapeseed oil etc tend to wax too easily (waxing blocks the filters, pipes and injectors) --- if in doubt, set you fridge to its coldest (not the freezer) and put a bottle of oil in it --- if it goes cloudy, it is useless in colder weather.
Point three:-
Blended with diesel at 5 to 20% oil added to diesel --- no mods are normally needed in most conditions (except Transits etc with lucas/cav pumps)
at 20 to 50% oil added to diesel -- no mods on longer journeys or where stopping does not allow the engine to fully cool (1/2 hr in winter upto 2hrs stopped in summer)
at 50 to 90% oil added to diesel --- no mods but make sure you put in fresh diesel hen parking up or it can be a sod to start in cooler weather.
Generally there are few problems with merc vans and mpv's if the thermostat is good (cold engines do not run oil very well -- 90c is much better than 70c)
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I run blended in all weathers, adjusting the ratio according to the weather (very, very roughly)
I always use Millers Diesel additive slightly stronger than the bottle says (4 to 6 measures in a tank) as it gets rid of the crap (see previous threads on millers from me and others) and stops "caramalising" when the engine is cold.
Low Sulphur diesel is better for the environment than older diesels but the sulphur acted as a lubricant --- you add the veg oil to replace the lubricant effect.
currently I am getting 47mpg from a 1997 108d that managed 32mpg when I bought it ---- No Mods ---- "blown through" with Millers diesel additive and straight diesel (one bottle in 2 tanks diesel) -- it ain't pleasant but it works ------- then the mix as outlined.
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If you follow the rules (1st in this thread) and use under 2500 ltrs in a year --- its fully legal NOW.
If you want to run on pure veg oil ONLY or to make your own bio diesel from used oil --------- I fully recommend
Smartveg UK - advanced diesel to veg oil car conversion system for recipes and/or full veg oil conversions.