I am now reporting that in at least one aspect (the most important one in my book), mileage. Ethos does not live up to the hype. I'll give you my results in a minute.
As far as a performance enhancer, I think this depends on many variables: the driver, the make of car, the engine, blah, blah, blah. Where some might feel a little increase in performance, another might not. The only way to really measure this, is to put the car on a dynamometer and measure it properly. Of course I don't have one in my garage, so it was just done by subjective feel and impression. Personally, I couldn't tell that much difference, but Sue said she could feel something. Your mileage may vary on this.
As far as reduced emissions, this is another item relegated to equipment designed to do so. I have no clue whether it made any difference, but I may save some of what I have left of the Ethos I bought to validate this when it comes time to reregister our cars.
Now for the big one, mileage. I'm disappointed to say that it made no impact. In fact, my own empirical data shows that it did just the opposite. Our driving is painfully predictable, so the driving conditions were nearly exactly the same from the start to the finish of our home test. We also tried different gases... economy gas (Costco), good gas (Chevron). This had no impact.
We drive a Mazda 3. The first tank without Ethos gave us 29.66 mpg. I never have checked the mileage on the Mazda, so I was pretty impressed, and looking forward to an increase. The second and third tank full with Ethos gave us 24.44 and 26.17 mpg respectively. As you can see, the mileage actually went down, and never approached the mileage without Ethos.
We also drive a PT Cruiser. The first tank without Ethos, yielded 22.27 mpg. about what I expected, maybe a little better. I ran three more tank fulls with Ethos. The first one gave me 23.31 mpg. Although it was a slight improvement, it was still within what I would consider the margin of error for combined highway and city driving. Not impressive enough to support the claims. My next two tank fulls yielded 20.79 and 20.28 mpg respectively. Certainly less that I got without Ethos, when I expected better. As you can see, it leveled off, giving a couple miles less per gallon than without it.
Conclusion: I don't consider Ethos the miracle additive that it's claims have made, and will not be using it in the future. I used about 2.0oz for each tank full, and at the price I paid plus shipping, this comes to roughly 3.75 a tank full, which is roughly equal to another gallon of gas. I should expect Ethos to extend my mileage by at least the mileage I was getting, not cut it short, making my tank of gas more expensive for the same or less mpg. So in essence, I'm not going to advocate using Ethos as a mileage enhancer. I'm sorry to those who have gotten better results, and feel it is the best thing since sliced bread. I didn't find it to be so.
