Where it's been manufacturer recommended by Honda and Ford; Is there any scientific data proving that 5w20 has not performed as well as or better than using a 5w30 would have over the same time frame? Is there any scientific proof that engine wear on these vehicles has increased in comparison to 5w30 and that the engine life of the vehicles using 5w20 shortened? Is there any scientific data to prove that the vehicles (Honda and Ford) in use over this time span have failed at a greater rate than engines using a heavier weight? I'm not referring to anecdotal rhetoric or viscosity theory. I'm am referring to scientific studies proving that 5w20 has not performed as well or better as say 5w30 or 10w30 over the same period. In other words, any empirical evidence that I should not continue to follow either Honda or Ford's (now others) 5W20 recommendation.