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I'm not convinced Texas engines run substantially hotter than NYC engines. They both have thermostats and radiators. 105 degree ambient summers in South Carolina and 65 degree Virginia days like yesterday, my temp gauge reads the same. Piston and valvetrain temperature are more a function of how you use the beast.
And I'm not convinced cold flow is really a concern. Bottom line is that you need oil pressure. An oil pump picks up a thinner oil easier, but it has a hard time maintaining pressure if the oil is thinner (it moves through the bearings more quickly.) Of course, my cars rarely experience starts below freezing, but really, if it's that cold, people use garages and block heaters.
Yeah, their test had some obvious holes. However, they needed a fleet of similarly driven, identical cars. But seriously, 6000 miles on a taxi is a ton of hours. What's their average speed? That's a lot of idling, and first gear grunting. If they didn't see differentiable wear under those conditions, then really. How many people would have guessed that the "superior lubrication properties" of synthetics wouldn't have shown up in this study?
I'll agree. Synthetics are shown to have lower viscosity changes across the temperature spectrum. Yes, they didn't really test that. As a scientist, I get paid to publish. Any responsible writer always has to acknowledge their holes and speculate possible findings under those conditions based on available data. They found that it's thicker when really hot, thinner when really cold - but someone's going to have to test if it makes a big difference under real operation. You can infer, but...
Personally, I want to have plenty of oil pressure hot and cold, so 10W-40 is my favorite for my operating parameters. Thinner would get better fuel economy, but I'm worried more about not-changing-my-engine economy. I watch my oil pressure gauge and decide what works best. I may even try 20W-50.
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