Mike,
I don't know the answer to you question.
If it were me, I think I would try some out on the missus's most favored roaster andthen put it in the oven at 110 degrees for about 2 hours. (any longer than that and sure as heck she will need it for something and you'll be sunk). See how simulating hot car conditions affect the stuff. If no bad odor or fire, then slap it on the car.
You're welcome,
Charlie
BTW: Be sure to clean off the tar stuff and return the roaster to its usual place. Then hope she never discovered your unauthorized use of it. And, keep your mouth shut.