Gas oil or 35sec oil is 2.00-5.00cSt - so is ULSD from the pump. Now I know that light fuel oil is 250sec and it's viscosity is about 8cSt - Corn oil at 80°C is 10.98cSt so that is greater than 250sec!
I don't have the figures in the "Little Black Book" for Rape Seed oil at 84°C however I do have almost all the other oils from 35° - 180°. So lets take Canola - Canola oil at 160°C is 4.29 cSt. Of the cheaper oils, it looks like Corn oil would be the most suitable oil as it has the lowest viscosity of them all at 95° of 8.56 - the best being Walnut oil at 8.21 - however, generally these are all quite high - so some mixing with DERV would be required to bring it down but it may end up more DERV than oil.
This is not really something that is ever encountered in a normal diesel engine but I wonder how hot a Bosch VE pump could handle pre-heated oil going into it. From about 145°C all oils are within the correct viscosity range but that is blinking hot - if that leaked out and sprayed over a red hot manifold you could be fairly sure of a good fire risk. At that all your fuel lines would need to be high temp stuff and you would need an fuel cooler on the return side as you couldn't end up with a tank of red hot oil sloshing about - the sender, among other things would melt. At this is sounds more like a mad experiment.
No one that i know heats any hotter than coolant temp - they generally start and stop on dino, and, when the motor is up to temp, manually swap (solenoid valves) to run the veg oil through a flat plate heat exchanger in parallel with the heater matrix.
I make bio for our 300tdi daily driver, as the savings from running on wvo would be cancelled out by then having to have a modified vehical policy (ie i keep the car stock, and modify the fuel) but the 101 is already on a modified policy, so, when i get around to it, ill put a secondary tank on that.
Indeed, ill probably install a webasto engine preheater, running on kerosene, so maybe not even bother with the diesel tank.
I assume your posted data is correct - again, i have a personal friend who has done about 8 years on a PD VAG engine so i can only conclude that the level of difference in viscosity difference makes no odds. Well, it certainly hasnt in his motor and im confident enough that it wont in my bosch driven 101. I spent a little time looking at tables of viscosities - your comment said veg was double or triple, but these things are still relative - i mean there were things on the tables i was looking at that you would still think of as pretty fluid, and they were tens or even hundreds of multiples out. I mean, if it was 3% out, im sure people would say that was unacceptable. 1%? 0.1%? I wonder how all these people who do manage to drive about on veg oil do it?
People are very quick to jump in with "it will break your car" - which it will, if youre a mug about it - if you take care and pay attention, then.... well all can repeat is i know (in real life, not just on forums - like i say, im keen enough to go to biofuel meets) people who have had long term success.
Sometimes (on the bio forums) someone will ask a question about how to fix their indicators / wipers / car radio, and ts rare that the comment does not come up "That will be the bio..." in mockery of those who things it breaks anything its within meters of.
Really, im not even sure why im getting sucked in to this one - if you want to believe that it will break your car, then thats fine with me. If you want to believe people on a forum who probably have no real experience in the area, but are just relaying what theyve heard elsewhere, then, again, i guess it makes no difference to my life.
If youre really interested, there are a uk forums - http://www.biopowered.co.uk is more technical, but with less traffic. http://www.vegetableoildiesel.co.uk is busier, but also has more noise.