Originally posted by Rara:
Unfortunately it isn't data I can post or do anything more than allude to, because it was Ford internal testing for proving out the use of the 5w20 oil. As far as I know, all the testing still passed Ford's wear requirements, but that it wasn't as good as the 5w30. Some of you seem to think that 5w20 will instantly blow up your engine or something, it won't it will work fine. The difference you would see, is if you took two identical engines, run them exactly the same for 100,000 miles, and then tear them down, and you will see more significant wear on the engine that has run the 5w20. It will be especially noticable for engines run in hot climates.

The real truth is just that it was done for fuel economy reasons and nothing else. It netted something like an overall 0.5mpg improvement in Ford's CAFE numbers, which meant big bucks for the struggling automaker.





Ah, probably that old one discussed at length on bobistheoilguy.com.

The truth is, not only is the difference in wear minimal, but it really depends on which oil we're talking about.

20w oils go up to about 9.1 cSt at 100�º C. 30w oils start from about 10.0. At those viscosity differences, it's just semantics.

When we throw HTHS viscosity cP at 150�º C numbers into the mix, this becomes even more the case. 20w oils go up to 3.3, which is above many 30w oils, which will drop below 3.0.