I would use a thermocouple in the gasoline to a data-logger. You can get simple data-logger from omega (  http://www.omega.com/subsection/temperature-humidity-data-loggers.html  )

It will be safe to put in the gasoline, just be sure to use a good fume extraction hood that is suited for combustable vapours and keep all metal in contact with the gas grounded and bonded to prevent sparks.

Drew K

I would use a thermocouple in the gasoline to a data-logger. You can get simple data-logger from omega (Temperature & Humidity Data Loggers)

It will be safe to put in the gasoline, just be sure to use a good fume extraction hood that is suited for combustable vapours and keep all metal in contact with the gas grounded and bonded to prevent sparks.