Originally Posted By: CATERHAM
The answer is no especially when it comes to OEM 0W-20s that have a very high viscosity indexes of nominally 220.
For example, while Toyota has back-spec'd their 0W-20 many years for most models, some older vehicles are spec'd for 5W-20 and not 0W-20.
The following is a quote of mine from another recent thread that includes the explanation as to why:
"A high viscosity index is generally better as long it is retained in service. And one should not consider an oil's VI without also knowing it's HTHSV. Why? Because the greater the VI difference, the lighter the higher VI oil will be, not only as one would expect on start-up but also at normal operating temp's for a given HTHSV.
For example, TGMO 0W-20 (VI 216) is much lighter on start-up than PYB 5W-20 (VI 150) but it is also somewhat lighter at normal operating temp's (say 90C) although both oils gave the same 2.6cP HTHSV. So if you want to maintain the normal operating viscosity with TGMO as you would have with PYB you'll have to increase it's HTHSV to about 2.7cP. How? One easy way is add a pint of M1 0W-40 . You'll lower the VI of the TGMO to about 210 but it will still be much lighter than PBY 5W-20 on start-up, have the same normal operating viscosity with the added benefit of a higher HTHSV rating for the parts of an engine that get very hot."
All that said, there are lots of people running TGMO 0W-20 and even the lighter Sustina 0W-20 in vehicles just spec'd for the 5W-20 grade without issue, but they are running a somewhat lighter than specified oil.
Of course if your vehicle is equipped with an oil pressure gauge then you'll know first hand how much lighter any particular 0W-20 is vs a 5W-20 and in most applications (but not all) the lightest 0W-20 it still more than heavy enough.
What happens to people who took your comments early on as in a year ago or so ago and ran out and bought the high VI 0W20 oils for their Ford, and Chrysler products calling for 5W20? Just a question that's all, no flaming or attacks intended. Lot of people were doing it I think. Not every one has an OP gauge a lot have stock idiot lights.