what do you guys thank of this idea?
 

here it go's my idea is having a marine battery in your car because with a car battery it takes a lot of its power to start a car and then the alternator charges the battery up. if you use a marine battery it wont lose as much power when you start your car and your alternator will not have to do as much work mpg!

Start by neasuring the temperatures involved.

I don't think this is much of a concern. People who designed return-style fuel systems have had to deal with the problem of heating fuel. Metal gas tanks and metal fuel lines seem to do a good enough job of shedding the heat. Whatever gets vaporized/evaporated will simply get sucked into the engine anyway as part of the EVAP controls.

brent777 -
Do you have some kind of fetish for mods that have the least possible effect?

Far less a "Hot Buton" and better suited is "penchant" and it's synonyms. :thumbup:

every little bit helps and go look at my mod list i got some cool stuff going on:)

i think the vent in the cap is for a worst-case-scenario. like a fiery car crash, rather than building pressure and rupturing in an explosion, the tank will vent in a controlled manner.

i don't want to discourage creativity and ingenuity but you're not likely to make any measurable difference to efficiency when it comes to the engine. if i were going to do any changes to an engine for efficiency, id rebuild it and lighten the internal parts as much as possible without affecting strength and balance, use roller bearings, port and polish the heads, and port match the intake and exhaust.

these are tricks primarily used by performance/racing enthusiasts but they work great for efficiency too because they play entirely upon reducing lost energy. lost energy in the bearings, moving heavy internal parts, and volumetric efficiency.

What car do you have that has a vented gas cap? mine has a check valve so it can let air in to replace the fuel that is being used, but it doesn't let air out, the only way for air to escape is via the evap system where the fuel vapors are stored then burned when the engine is running.

Its been decades since gas was vented directly into the atmosphere. Any vapors are contained in a sealed system, then they are purged by the running engine, with the oxygen sensor correcting the normal injected fuel to compensate for the inhaled vapors.
Net result no difference in mileage.

regards
Mech

even if, and its a big if, your system worked as designed, i think the small additional drag of air through the cooler, and small amount of weight added to the vehicle could negate your gains