Phase separation of gasoline — avoid it if you can! I’ll tell you why and have a simple experiment that lets you measure the ethanol content in your gasoline too.
Phase separation (PS) is what you can get from the ethanol content in your gasoline. It can damage your engine and possibly get you stranded at an out of way place. It is more likely to occur with lubricant-added gasoline used for two-cycle engines commonly found in ATVs, outboard motors, motorcycles, snowmobiles and other equipment with small engines, but can also happen with regular gasoline.
“New” Gasoline
Gasoline without any ethanol used to be what you got when filling up your gas tank a decade ago or so, but the wannabe-savers-of-the-world had a “better” idea. Why not dilute the gasoline with ethanol. At first your “new” fuel was limited to an ethanol content of 5{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} (E5). Then the US Environmental Agency (EPA) mandated up to 10{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} ethanol content (E10) and as of late EPA is talking about a 15{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} ethanol (E15) mandate.
If you have experienced problems with E5 or E10 gasoline, E15 could just about be disastrous. The main reason is that the likelihood of PS occurring increases exponentially with the ethanol content in the gasoline.