Originally Posted By: 440Magnum
That's not entirely true, or at least the more viscous oil doesn't necessarily flow in the same pattern through the engine, as demonstrated by skipping to 5:00 and following in this video. Same exact engine (with the same exact oil pump) started at -34C with different oil grades with the valve cover off and watching flow from the cam tower squirters...
https://www.youtube.com/watch?v=OWiQyR7PWII
Ignore the salesman voice-over about "metal-to-metal contact!!!" but the difference in actual oil flow is obvious. The pump may be displacing the same amount of oil per turn, or it may not. The thicker oil may be causing the pump to cavitate. Or it may be causing the pressure relief valve to lift rather than pushing the thicker oil to the last cam bearing in the system.
Of course as others have pointed out... this is not an issue that will EVER happen in Florida. At least not in this geological epoch...
You have to understand that in that Esso video they took two oils, one that was within it's pumpability rating for the test temperature, which I believe was a 0W (-31F rating) and the other was not, which I think was 10W (-13F rating). This is very deceiving to people that do not understand how the W rating is obtained or what it really means.
What this video clearly shows though is that the W ratings are important and should be used according to the outside temperatures the vehicles are operated in, otherwise the oil will be very difficult to pump and hence take longer to reach various components, as demonstrated in the video. However if they only picked a 5W rated oil (-22F) for their test, which coincidently was also done at -22F, there would be virtually no difference in flow because both oils would've been within their pumpability limits.
Pumpability and thickness are two different aspects in positive displacement pump oil systems.
What this video also shows is that oils that are outside their W rating temp. will still provide adequate protection and there is no "dry" start. So they are perfectly fine for an occasional very cold start, but as the video suggests, for vehicles regularly operating in very cold climates, a properly rated oil is the best.
Here are the W rating temperature limits:
0W -35C (-31F)
5W -30C (-22F)
10W -25C (-13F)