Ethanol free gas?

[911monty]

Originally Posted by MWS

For daily use, definitely the higher octane w/ ethanol. For long storage, the ethanol free. I never really bought into the "fears" of keeping the ethanol fuels over time, but I was wrong. In as short as 1 year, they can begin to gel and cause all sorts of problems. Thankfully I didn't discover this in my Boxster, but in a pressure washer....totally gummed up the carb, which resulted in having to disassemble and clean. Learned my lesson...for any item I use infrequently or store, I keep ethanol free fuel around, don't even mess with adding stabilizers.

Fuel "gelling" is actually caused by evaporation of the volatile components of the fuel and leaving the heavy "varnish" behind. This varnish is what plugs jets and coats the floats in a carbureted system. This will happen with free or ethanol fuel. Best practice is to run carb dry or drain for storage and use Stabil to minimize varnish formation.

Carburetors are prone to this issue since they are a vented atmospheric system, this allows the volatile components aka "light ends" to freely release to the atmosphere until everything in the carburetor evaporates and dries out. Gasoline in an EFI system is enclosed and does not vent to the atmosphere. Since the system is closed the volatile components will vaporize only until the Reid Vapor Pressure (RVP) of the fuel is attained. This is the point where vapor pressure is in equilibrium and the light ends no longer vaporize but remain in solution. This pressure is the pressure you release when you remove the gas cap. There is a standard RVP for fuel and it is typically ~7-9 psi. Just FYI.