Originally Posted by oilman
Unquote:
You see thicker was better when all that was available were mineral oils but chemistry and oils have moved on and synthetics have given birth to a breed of tougher lower viscosity oils which are superior lubricants in every area.
I cannot dispute that. But quite common experience of competition/hard road use is that e.g. high power turbocharged engines tend to use MUCH more thinner oil. I mean thicker ones usually greatly reduce oil use and that is also in new engines - so it's not engine wear. The other thing is that though I am no big expert th xxWxx numbers tend not to show all the oil capabilities - if you study very carefull producers numbers oils which are the same viscosity e.g. 5W40 can be of completly different actuall viscosities in operating temperatures. As far as I remember firts number is in 0 degrees and the other in 100? I understand then modern synth oils are very stable in high temperatures but there is some point at which their qualities degrade and so I was told (in example by people from Castrol Poland) that as a general rule you can think that this happens to thicker oils in higher temperatures.
If there is no point for such thick oils why eerybody uses them? And why the thickest synth oils are the most expensive and adviced to be used on the ost advanced sports-car engines?