http://www.biodiesel.org/pdf_files/f.../Lubricity.PDF
I'm going to add 1 liter bodiesel to each fresh tank of diesel.
Above article suggests it is a great lubricant.
Our cars can take up to B7 according to my fuel cap (7% biodiesel). Fuel in my area may already have up to 5% biodiesel. Our tanks are about 60 liters capacity so 1 liter of biodiesel added to 60 liters is 1.6% --- I think it is safe. Too much biodiesel can damage motor b/c it has a higher flash point and can be left uncombusted in the exhaust phase when our motors inject at times to burn off accumulation in the PDF......or so I understand it. Unburnt biodiesel could damage our oil is my understanding.