My car is a automatic and I drove the car on the freeway while it was in 2nd gear (the one below the "Drive" gear) at 60-70 MPH for several miles without noticing what gear it was in. At the last minute I saw that white smoke was coming out of the exhaust and the did not start up after I shut it off. I returned a few hours later to see if it cooled down and it started but the engine heats up almost instantly. What can be the cause of this, how can I fix it and what did I do to damage the vehicle in the first place. Please & Thank you