I'm sorry about this one sentence in my reply. I was so caught up in my reply and wanting to get it posted that I forgot something. The 0W40 I used was EURO Castrol. For some reason it made my engine run somewhat more quiet then the other weight oils I had used. Maybe because Castrol oil is thicker? When my engine got up to operating temperature the thicker 40 weight made it quiet? My engine has never made any loud valve train noise with 5W20 and 5W30 oils. I can't explain it. But, I have always believed that all Castrol oils were somewhat thicker then other oil.The 4.2 V6 in my 07 F150 was built 1997-2008. In all those years of production the tolerances and clearances had NEVER changed. Up until 1999 the spec'd oil was 5W30. In 2000 Ford spec'd 5W20 for CAFE reasons ONLY. In the 159K miles on my engine since new I have used 5W30 about 90% of the time. And, I can't tell the difference between that and 5W20. I have also used 0W40 a few times and couldn't tell the difference with that oil either.