Ok heres the issue had a used motor put in my truck. When you first start it up it runs great no knocking. I take it one about a 3 mile drive it starts knocking really bad. I just put new oil filter and 5-30 syn blend in it. Now another mechanic says to use conventional oil 5-30 because it is thicker.So now it will be third time in less than a week changing my oil does that seem right to you guys?he said same thing as me when it cold it runs great but after it warms up it knocks. Temp gauge is reading fine oil gauge seems fine too. too me it seems like its either heating up or not getting enough oil.

 

If there's any kind of warranty on that used motor, use it. It's shot.