Originally Posted by
lilman320
This is off the Ford Fleet Website...
5W-20 oil is a thinner oil with lighter viscosity that creates less drag on the crankshaft, pistons and valvetrain. Additionally, the oil pump can pump thinner oil more easily, improving oil circulation. Any increase in fuel economy may not be noticed by the average motorist. Machined internal engine parts are more precise than the parts of 20 years ago. This means that clearances between moving parts are smaller and more exact. Thinner oil such as 5W-20 can flow more freely through the engine while still filling the spaces. Thicker oil is harder to push through the spaces between the parts. This causes the oil pump to work harder, which in turn increases oil pressure while simultaneously decreasing oil volume. A lack of oil volume results in a decrease of lubrication and cooling, which may decrease engine part life.
The lighter viscosity of 5W-20 oil flows faster at start-up compared to higher viscosity oils, which helps reduce engine wear in critical areas by lubricating parts faster. Valvetrain components at the top of the engine require immediate lubrication at start-up.
And that was written by the marketing dept, not the engineers. The fact that Ford itself recommends 5W-50 for at least 3 different US Modular applications casts those comments in a rather dubious light. A primed oil system will circulate oil through the engine almost instantaneously regardless of viscosity, unless the the thicker oil is simply too cold to pump. When talking 0 deg F and above, the different in viscosity is minimal in regards to how fast it moves through the engine on cold starts.
Then there's the fact that many synthetic 0W-30 and 5W-30 have superior cold flow properties to Motorcraft 5W-20. The issue isn't as simple as some would have you believe.
I'll say it again, 5W-20 will be fine, 5W-30 will be fine, 10W-30 will be fine.