my check engine light has been on and I got it diagnosed and was told it was my evap and that I needed a new gas cap.....will this leak in my gas cap allow for a significant evap of my gasoline?

 

It will be a slow leak; gas caps are cheap; I bought a locking gas cap made by Stant at the local parts store for about $12.

 

A faulty or loose gas cap can easily lead to the SES light. As mentioned above, they are very cheap. I picked up one from the dealer, can't remember how much I paid, but I'm pretty sure it was around ten bucks.

 

you can start there, but it could be somewhere in the evap system itself.
It is reccomended starting there because it is the cheapest fix.

I traced my system when i got an evap code and to my discovery I had a small hose unplugged underneath the hood. (most likely happened when I was working on something else.)