At a risk of taking a lot of flak from some members on here, I always do and have been adding to my fuel for a long time. Again, at a risk of taking flak, I use Sthil two stroke oil. Why the Stihl two stroke oil, well I think the oil is made to add to fuel to lubricate, and as I use it for my saws and buy it by the gallon at a good price, so there always some in the shed. Occasionally I put some in the fuel of my car, a 4 year old Mercedes, and I also add a small amount to the petrol [Gas] of my mower. My thinking is that the fuels today have had a lot of the additives removed for pollution reasons, and are too `dry`. I never seem to have any problems with my engines even though I been doing it for years. Our cars have to be tested every year, and mine always come back and is always well within the limits. It might just be me, but I think you can hear when the oil gets to the engine as it seems to run sweeter. I did have an old diesel fishing boat, and that old engine was as good when I sold it as it was when I bought it after many hours of hard work.