No
Diesel.
No it will not give you better performance or increase gas mileage. Gas mileage and performance will decrease only if you use it. leaving it off is like not having it at all.
No it does not give you better gas mileage, all it does is helps with any loss of horse power and white smoke coming from the tailpipe due to burning antifreeze.
Yes, higher octane gas does give higher gas mileage for your car. However, the increase in gas mileage may not as great as the increase in the price of the higher octane gas.
for any car to get better gas mileage get a better flowing intake and/or exhaust or get it tuned
New spark plugs with the proper gap will give your car the best possible gas milage.
It could, if the old gasket had failed.
Yes it can, depending on your driving habits.
Bicycles give you more gas mileage.
No it does not. But it does give you somewhat better gas mileage.
This was answered on an episode of Mythbusters, you get better gas mileage with the AC on.