So far on researching and reading online testimonies I have not found any negatives except for no improvement in MPG. Yes there's always chance of something going wrong by doing it and messing something up (actually you'll more likely to ruin you paint job by spilling some on the paint) You can bet no car manufacturer is going to recommend or approve it if something goes wrong with your car least of all cover it under warranty. However there is risk in everything, there a risk everytime you step in your car. Albeit a small risk I feel it about the same about as Acetone. I have tried for the last few tanks and there is some improvement yet unfortunatley I did not record any data on before starting it. So where I see the improvement is going up hill the MPG gauge is definetly higher than before.