Engine rod knock is often caused by low oil levels. Your engine requires oil to lubricate moving parts, as well as cooling. Without sufficient oil levels in the engine, there is bound to be excessive heat as well as wearing of parts, and this will lead to a rod knock. If your car gets an engine rod knock, you will most probably need to have the lower half of your engine replaced if not the whole engine, depending on the extent of damage. It will normally affect your pistons, crank shaft and rods. Replacements of these parts will cost you quite a good amount of money and time, as your car will have to be in the garage for a while after experiencing an engine rod knock.