We're discussing 2 conditions here which shouldn't be confused with each other. When a engine is first started the oil is cold and thick. It will read high on the guage. As it warms up it thins out, reducing the reading. Depending on conditions the difference can be anywhere from 10-20PSI to 1-2PSI, unreadable on the average guage. The other condition is when the engine has reached it's operating temp. In a perfect motor the the PSI will remain the same from a idle to 5K RPM. Not many motors are perfect. The average engine will show a 2-10PSI swing. A motor with loose clearances can show as much as 20-30PSI change. In order of wear the cam bearings are least, main bearings next and rod bearings showing most. There are exceptions but geeez, be reasonable. The loose bearing gets most of the oil and the tight bearing gets less. Drag race from the stop light, hi revs before shifting, or just plain high milage And bingo, the tight rod goes thru the block, and or pan.