Question about car warrantys?

well i recently bough a used 2007 doge charger with low miles from some guy he gave me a good price so i got it but now i kind of regret it because it stared to give me problems it stared to overheat so i immediately got a extended car warranty since the factory warranty was expired they didn't ask for car inspection because of the low miles so i got it.so a month after went to a car shop i got it checked and it was something with the engine very expensive. now im not sure if they are going to cover it i did not know that the car had preexisting problems .could they find out? would they cover it i have "bumper to bumper".