I used this stuff a couple of years ago on a citroen hdi I had it was low mileage and in good nick but lacked power for a 136hp version, I thought it was because the little old dear who had it before me hadn't taken it anywhere at more than 30mph. it gave superb short term results improving the power and fuel economy, it wasnt until about 12 mths later it started to go wrong at first i didnt make the connection, first off the head gasket went and at 38,000 miles was a bit of a shock, but just thought it was one of those things and got the garage to sort it. they stripped it and I got a call from them telling me that when they removed the head the valve stems were worn and there was some scoring on the bores they said it looked like something had caused the engine to run hotter and caused a lack of upper cylinder lubrication but they cannot find any cause for it they also said it was extremely clean inside the combustion chambers etc I told them the only thing that i had done was put fuel in changed the filters and put in a fuel treatment, it was when i said this that the guy said that explains it then, I didnt know but chemical solvent fuel additives cause your engine to run hotter in the combustion chamber and not only remove carbon but also break down lucricants in the cylinders.
so a word of warning they only give positive results short term and can cause more harm than good long term and if there is a slight problem they can cause it to rapidly get worse. now I'm not blaming BG for the problem but with what I have learned about fuel additives, that is the last time I use one.
one question to ask is why do the fuel companies not put what ever is in these additives into the fuel to start with, it would be a good marketing opportunity our fuel keeps your engine clean. I will tell you why because they can cause damage and that is why.