My thermostat went and i replaced it but didnt bleed all the air out and the engine over heated. i brought it to the ford dealer and they said i had a lower engine knock and needed a new engine its a 01 cobra engine with dual overhead cams. it burning oil when i start it up. i got a estamate for 8 thousand dollars for a new ford motor would that be the best way to go or is their any other options that cost less money. the car has 40,000 miles on it.