Well it's been several weeks since i poured a bottle of Tufoil into my engine. Reason I tried was because i had run a little low on Motul 8100 5w40 which tends to burn off easily. The bottle of tufoil was not enough, so topped up summore with Castrol RS 10w60.
Result: (Driving a Mazda 323 hatch, B8 180 engine)
Very little improvement in fuel economy, if any (maybe 5% or less). But that's hard to judge because when I started using tufoil coincided with the increase in petrol price. I'm just a normal driver on the roads. Hardly boost one.
The engine SEEMS to run smoother ONCE WARMED UP. Please note this is a highly subjective opinion. However, on cold starts cranking seems to take a little bit more effort and tappet noise now takes a long time to go away. However, once the engine is properly warmed up, everything is smooth and yummy.
I also seem to note (SUBJECTIVELY) that the turbo now spools up faster. This may be due to the reduced internal friction as I'm running on a journal bearing turbo. So the oil does play a big part here.
That's all for now. Please also note that when I started using Tufoil, my Motul was half way through its useful life.