I have no doubt that a 0W20 or 5W20 in an application calling for that weight might protct it just fine. I do doubt though that 5W20 is the best comprimise for most engine designs and driveing cycles. This is especialy the case for trucks actualy being used most of the time as trucks/work vechiles not HWY qeens.
I also find it interesting that for the most part this huge push for 20Wt. oils started in N. America were or crazy CAFE system encourges it's use by default. Sure Japan is starting to get the push for 0W20 and 5W20 oils now as well but hat leaves a huge part of the world out. It is hard to push something as counter intuitive as running a thinner oil for all driveing conditions and temp.'s! Remember most drivers in other countries still get to chose the viscosity they want to use from a viscosity chart in their owners manual. It has only been the USA that has been pushing a single weight as the recomended viscosity. THis has only been going on for about 10-15 years and started mostly with the domestic brands and has only slowly trickled over to the imports. CAFE has had a huge inpact in this area. Last I checked Mercedes,BMW,Audi and Hyundai(sp) are the last companies that still give their owners a choice of viscosities on vechiles imported to the USA. Feel free to correct me if I am wrong.
Oh I almost forgott!!! You know this whole thinner oils flow better debate??? Well not only does the oil flow into the parts,spaces and cavitys faster but it also flows out of them faster. This means that when under load the film is going to be squeezed out from between the two floating surfaces faster as well. Now under normal conditions this does not mean much but under shock loading conditions, over heating, detonation even momentarily this makes all the difference in the world. It could also make a huge diffence under high load low rpm conditions.
Someone mentioned that the Ford GT requires 5W50 oil instead of 5W20. Aside from the super charger the block,oil pump,rods, rod bearings,crankshaft,crankshaft bearings and all of the clearances on these parts is basicly indentical to the normal asperiated modular ford block. This alone should demonstrate that 5W20 is not the ideal compromise for this engine series! No one designs an engine around an oil the oil is always picked after wards as an after thought to meet minimum durability standards and to maximize fuel effiency. In the case of the GT CAFE is not an issue so only durability is an issue with the oil selection.
