[mwebb]

all systems run most of the time at an
Air to Fuel ratio of 14.64 to 1
1 part fuel
14.64 parts air
by weight

so
1 part of fuel will have much less influence on the temperature of the complete mass entering the combustion chamber than the 14.64 parts of air

and
on systems that have a return line
that extra unused very heated fuel goes back to the fuel tank , heating the fuel in the tank
which causes heavy duty evaporation and pressure build up in the fuel tank much of that pressure and HC
can
be vented
to atmosphere
because most systems are not designed to handle that scenario
fuel vented to atmosphere does not increase FE as it is
wasted

10% improvement .... not very likely

Originally Posted by smokey442

I have found that heating gasoline to 180 deg. F yields about a 10% return improvement in fuel economy. Detonation threshold seems about the same for a given octane value. Greater tendency to vapor lock during hot restart. Most OBII ecu s have the ability to recognize this condition and will keep injectors closed until engine restarts. May take 2 or 3 tries but it will fire up. Heating intake air also improves fuel economy but I have found a greater tendency to go into detonation especially when ambient temps. go above 60 deg F. If you run a dedicated water or water/methanol system you can effectively supress detonation with even the lowest octane fuel.