The level of engine protection as a function of only oil viscosity really depends on what your expected maximun oil tempetature is going to be. Higher viscosity oil doesn't thin down as much when the oil temperature increases. This is why car manufacturers spec higher viscosity oil for track use, because they know oil temperature is going to get higher and thin down more than normal street driving. Get the oil too hot and too thin from heat and the minimum oil film thickness can decrease to the point of metal-to-metal contact (wear).
It wasn't just the Boss 302 that had 5W-50. The regular GT with the Coyote that had the track package on it also came with 5W-50. What do you have to say about that?
I neglected to mention the regular GT track pack, so thank you for pointing that out. The same motivation as the Boss 302 with respect to CAFE would apply. Because the company is judged as a fleet, lower-volume vehicles (of which that trim level of the GT would counted as) are afforded the opportunity to shift the balance more towards performance at the cost of fuel economy.
Not really, because that temperature and lower ranges are only experienced during warmup (i.e. they're very temporary compared to the lifespan of the engine). The engine itself is designed to run with oil temperatures more in the 185 to 205 F range.
I don’t think any of us disagree with the motivation you cite here.
Ok, but a 0w20 could be upwards of 400 cst viscosity at cold start. A 5w50 might be 17 cst when hot, while a 5w40 is 13, a 5w30 is 10, and a 5w20 is 9. My point is that if 17 is bad and could shorten the life of the engine, wouldn’t a viscosity 20 times higher be 20 times worse and very concerning? I think people get too hung up on the hot viscosity number, not realizing the temp affects the viscosity far more than the sae weight rating.
Based on your numbers, the 50-weight is still almost double the kinematic viscosity of the 20-weight, so I don't think that can be ignored, especially over the the course of 100,000 miles (if we're using Ford's powertrain warranty metrics as a the basis by which the engine's expected lifespan is determined). Components like cam phasers, their complementary solenoid valves for introducing and draining oil into the phaser cavities, and lash adjusters are very sensitive to at-temp lubricant viscosity due to their small sizes and very narrow oil passages, so running heavy weight oils long-term can diminish those components' expected lifespan.
And again, orders of magnitude less viscous than cold 5w20 that no one seems to worry about at all.
And again, all of these components go through the same warm up cycle with oil in the 400+ cst range every time the engine started, so I don’t think 17 cst is going to hurt them. Not to mention, higher viscosities offer a larger film thickness under heavier loads and higher temps, which results in less wear.
You hit the nail on the head earlier. It’s fuel efficiency only that is driving the industry to lower viscosities. They are pushing to lower viscosities and testing to see if the engines can still meet the oem lifespan goal. Some are modifying the engine designs to retain some lifespan with lower viscosity. E.g. modify the engine to deal with less oil film thickness. I think this is craziness. In most cases it will be just fine because most engines rarely exceed 30% load. But enthusiasts generally are harder on equipment than the average joe.
