I own a couple carbon fiber spinning and casting reels. I keep my rod and reel setup in my car and just wondering if the cars interior, if it gets past 100 degs, will the heat warp my reel or soften carbon fibers?

nope maybe past 1000

No.

Negative

Not likely, but being baked like that for a long time, the grease and oil inside may breakdown and vaporize, also some small plastic (not carbon) parts may get damaged.  I would just put a reel that I don't care about much inside the car all the time.

I think it will be more detrimental to your line than anything

170 degrees is likely where the resin will begin to break down. 

They'll be part gas and part soot by 500 degrees. 

It's not the carbon that will soften but whatever polymer makes up the bulk of the material and that's still of no concern.  Its not going to deform at hot car temps or become weak from having been heated.  The stuff was already molten once when it was made. It's just plastic with a ground carbon fiber power in it for extra strength over the base polymer.