I hear all that your saying people
first of I never said thicker then recomended
i have had and have three vehicles over two hundred K and one gas engine to 500 K - rember I'm RR
still say don't care what anyone else says (if you use the thick end of what's called for and you warm up before driving - like I do 95% of the time - your ride will live longer.
i also hear what you guys are saying about multi grade viscosity and I'm clear on your points.
I took part as a lurker on a dodge diesel forum about 5 years ago in about a 50 page debate on the subject. One thing that I was not aware of and still not sure about is this- 10-40 is not 4 times less viscous hot then cold so 5-40 May never be as thick as 10-40 even at 100 whatever-anyway that's something I took away from that ridiculous long debate but never fully confident about the many arguments both then and now.