I know this is a really old post, but i thought I may be able to enlighten anyone else who is reading this.

To start with, you have a chippy, which oil do you use?

The most common oil chippies use is palm oil.

PALM OIL I do not recommend using palm oil as a feed stock for making bio diesel, because it is solid at room temperate. This means any un-reacted oil left in the bio-diesel will also become solid. The properties of the bio-diesel once made will mean that it will gel up around 15 degrees C. You don't want this happening in your fuel tank, living in the UK it will.

You may well be frying in groundnut oil, soya bean (AKA vegetable oil) or rapeseed oil.

All these oils are fine for making bio-diesel.

You can follow this link to see the equation for making bio-diesel

Please bare in mind, this is an equilibrium reaction, to therefore you need to add extra methanol than actually required, then remove the excess. The other 2 options are to react twice, whilst removing the byproduct glycerol.

Now you must consider the cost of actually doing the conversion.

Everywhere will say it costs 10p per litre for the reactants, this is true. But you still need to factor in the fact that you could have sold the waste cooking oil to a collector:

Waste cooking oil collection service for around 20-25p per litre

or gained a better deal from your fresh vegetable oil or rapeseed oil supplier by returning your waste oil to this company.

You must also look at the initial cost of the equipment, waste disposal costs for the glycerol, cost of failed reactions and the cost of the "what if i put substandard diesel in my car" then there's the cost of repairs. Fuel tank cleaning isn't cheap, neither is a new fuel pump or injectors

I'm not trying to put you off here, you just have to factor it all in.

I reckon the actual cost of producing the fuel, is somewhere more like 60p per litre.

I would say the real driving force for you producing the fuel wouldn't be to save money, but more that you enjoy the challenge of this organic chemistry.

This is coming from someone who has produced fuels in the past and has made the mistakes.