Better not put any pepper spray in our cars. The can instructions say to store in places no higher than 120 deg F which is 48 deg C. The ambient air inside the car cabin (with tinted windows) can reach up to 50 on a hot day. I got this info from two separate tests in local Malaysian conditions.
Worryingly, I also read from the net about people's experience that their pepper spray canister leaked inside their car. They didn't explode like a bomb, of course, but they leaked the fumes into the car cabin. This happened in the US (summer). If it can happen there, I think it can certainly happen here too.
I am sure the true safety limit for the temperature is higher than what is stated in the can but I rather not risk it. Scared I might get self-pepper sprayed while driving one day.
However, I did find out that there is one brand of pepper spray that can be stored in slightly higher temperatures but that isn't sold here. Also, during the Safety Campaign Demo I attended, someone mentioned she put 4 pepper sprays in her car! One at each door...