There would be several reasons to capitalize: the device can be used for several years; cost is about 10 percent or more of auto cost and more important, it could be a betterment because of possible operating cost saving. However, I am trying to convince myself to expense it, reasons are: the cost saving might not be significant enough to consider it as betterment (some auto mechanics say it will save more than 50 percent than gasoline, but no authoritative sources), and one main consideration for conversion would be it is environment friendly.