Why does my engine make a knocking sound when I start my car?
Welcome to just answer! The term rod knock is a serious problem and I do not want to go there without having heard the car or asked a few questions. First, please check your oil level before you start your car again. Does this knock go away after say 5 seconds of running the engine? That would mean you have a rod noise but only while your oil pressure is building up. Engines can do that for years without failing but is not a good sign. Rod bearings alone with most of your engine bearings consist of two smooth surfaces that oil is pumped in between. The space between these two surfaces can increase with wear. If they increase too much you can hear them knock. If they knock all the time the end is near for your engine. However, there are other things that can knock in your engine. Pistons can rock back and forth in their bore and make a sound that is hard for an expert to distinguish from a rod knock. I cannot do it from here with only a description to go by. How heavy is this noise and how constant?
Well it only does it during start up sometimes. If the engine is already warm from sitting outside in the sun all day, I wouldn't hear the noise, but if its cold I hear it sometimes.
That is very cold news indeed. No repair is practical at this time. Maybe a little thicker oil or additive will help minimize this condition. Do not go overboard! I do not want to switch to straight 50w or anything that extreme. Just live with it as long as it quits soon after starting.