Why cant I use Bio Diesel ?

[everogere]

I have just purchased a A4 Advant 2.0 TDI and have just filled up with fuel for the first time. I used Shell Bio Diesel. I have noticed smoke from the exhaust today which I dont think was there before I filled up. I also notice in the handbook and on the filler flap it says not to use Bio Diesel. What I need to know is why cant I use this and now that I have, would it do any damage and would it account for the exhaust smoke? Thanks

[s4marsh]

it might not be reccomended as the fuel pump or seals used must not like it probably due to certain additives i cant see one tankfull being that harmful for it just dont tell audi

[johnnythepie]

Id be tempted to drain it

[dunk]

bio per se isnt the problem, as most euro or uk mixtures are only 5% or upto 30%

there are a couple of potential problems:
1) the bio is a far better solvent than diesel and it washes out all the crud from your fuel lines, filters etc resulting in a blocked fuel filter - this can result in a misfire, failure to accelerate or smokey drive as you get uneven fuel delivery - it goes away as soon as you change your filter and is worse the higher % of bio

2) any properly made bio wont have too much methanol or soda left in it so wont rot your filters, lines or seals any more than petrol or diesel - homebrew or cheap ebay stuff may not be washed properly but anything made to en standards for europe should be ok

3) you do get slightly less power cos the bio has less energy in it, but you are talking 5% or less

4) the higher viscocity may cause problems with the later peizo injectors, but again 5% to 20% mixes really shouldnt be a problem

5) audi cars in europe have to be made to take bio cos all their diesel contains 5% minimum by law, they just insist on the uk cos there isnt the infrastructure to deliver en standard bio to the same level

i ran my 2.0tdi on 80% bio both in standard, chipped and then hybrid big turbo for 2 years without any probs except for the blocked fuel filter at about 1000miles. i got imported eu bio at 60p/L and added some diesel and millers to ensure a good cold start.

[everogere]

Thanks Dunk that was very informative and exactly what i needed to know. Thanks