Got up to 50mph and the motor started knocking, sounded like a sludge hammer hitting the engine, pulled off road couldn't tell where it was coming from. When hitting the excelerator it got faster, then a large bang, and engine quit, wouldn't turn over to restart. Looked under truck and alot of oil started pouring on the ground any ideas of what it could be? Thought at first it was a rod going through motor, has 218,000 origanal miles on it. Can anyone help? This all happened in less than a half mile. After letting it sit for a couple of weeks turns over, made a knock the first time then just cranking.