I have seen an increase in biodiesel use, and “naughty” fuel use, i.e red diesel, kerosene, parafin, marine diesel, heavy oils etc, these have either been the cause of a fuel problem or been evident in the tank residue , these are all duty evasive fuels that have not had 60p fuel duty paid on them, or 25p VAT, it can seem attractive to use cheaper fuel at the current prices, aside from the moral and legal implications I would not recommend trying to cut corners with fuel.
No one needs told that fuel is getting pricey, my brother told me today that litre for litre supermarket ownbrand cider was cheaper than diesel, (chances are diesel tastes better than supermarket cider).
Modern engines have very low tolerances for fuel variation, kerosene can overheat an engine, marine diesel is too thick to pump, red diesel although having identical properties to white diesel can incur a heavy fine, the serious downside is duty evaded fuels puts the user on the wrong side of the law and since duty free fuel is often sold in the black economy, the chances are it has also been stolen from someone, which makes the user party to a criminal supply chain.
I have also attended a number of BIO diesel “misfuels”, this is cases where biodiesel was used but it did not agree with the car, or was low quality or contaminated with water, a full drain and flush was needed to correct the problem, I think Biodiesel is a great idea and encourage it, the use of it is covered extensively on the net, if you do want to use it, 1) check and see if your car is compatible with it – on the various biodiesel forums and 2) get biodiesel from people who know what they are doing, badly made biodiesel can be contaminated with water or solids and can cuase problems.
If you have used biodiesel and it doesn’t seem to be working for you, you could either thin it with clean diesel or depending on volume have a fuel drain, I would be happy to advise – and I won’t try and talk you into a fuel drain if you don’t need one.