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.
It could, if the old gasket had failed.
It could.
No
are you sure its just a blown head gasket?... if heads are warped due to overheating replacing the gasket wont help you will need new heads as well. You can get a Haynes Manual or Chiltons, they will give you step by step guidance on replacing your gasket.
Diesel.
yes and more horsepower
63km/ltr
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.
Yes it can, depending on your driving habits.
No it does not. But it does give you somewhat better gas mileage.
Bicycles give you more gas mileage.
The gasoline that is recommended by the manufacturer is the best fuel to use.