Loud knocks in your engine are not to be ignored rather you have to pay attention and give immediate inspection before it leads you to a severe situation. I would like to share with you an experience to explain what this means to a car owner.
My wife and I traveled around 60 kilometers distance using their 1996 model Toyota L, Tamaraw series, jitney type AUV. Approximately 30 kilometers far from our point of destination and where we are bound to, we have noticed knocking of the engine.
Hearing that tolerable but disturbing sound, the loud knocks, we continued and were able to reach a ten-kilometer distance. As we climbed up the road the car stalled. We rested for a while to cool the engine that is above 180 degrees F temperature. Maybe the temperature gauge was not functioning correctly because 180 degrees is still tolerable.
The engine was started and upon trying to advance had a loud knock and right there, the engine is dead. We left the car in the rural site taking a bus downtown. The following day the car was towed to a mechanic to their shop for an engine overhaul.
Possible causes could be traced from several reasons like overused oil, lack of oil, defective valve seats, valves.
Never ignore symptoms rather address it immediately and you will save time and money. Check here.