Heat is the most damaging you can do to your bow. If you need to leave it in the car, get the windows cracked, try to park in the shade, or at least get your bow on the floor and covered with something to keep it out of direct sun.
I have saw this happen three times I can think of. Yes, the heat and sun through the glass will make those nice lmbs wacko.
Same thing can happen if you keep it stored in a shop. If it gets hot hot….not good friend.