Hi. My car is well maintained. I had a checkup recently. But, when I was driving the other day, there was this loud knocking noise in the engine. I was going uphill on an interstate at that moment. I decreased the speed and pulled off. The car kept making the horrible knocking sound even while idling. The mechanic said it is an internal engine damage. At the moment when the engine blew, there were no leaks. The oil I was using was synthetic. Do you have any idea why this happened? I appreciate your help.
It sounds like you may have spun a bearing in the engine on the crankshaft or piston rod bearing. Depending on the cause you may have:
lost oil pressure going up the hill from the oil pump sucking up air from a leak in the oil pickup tube, or
the pump just failed.
You did not state how many miles your engine has on it; this could have been from normal wear if you have very high mileage. Having the engine knock inspected by a qualified mechanic would be a good idea.