Originally Posted By: tig1
I used M1 5-20 in 1978 in an engine calling for 10-40. No CAFE then and the 5-20 performed very well.
Quote:
Enacted by Congress in
1975, CAFE's purpose is to reduce energy consumption by increasing the fuel economy of cars and light trucks. NHTSA has set standards to increase CAFE levels rapidly over the next several years, which will improve our nation’s energy security and save consumers money at the pump.
https://www.nhtsa.gov/laws-regulations/corporate-average-fuel-economy
Again, and we've been over this ad nauseum...
in 1978, 10W40 was a woefully inadequate grade, and was one of the primary drivers for research into High Shear viscometry, where it was found that the temporay and permanent shear on this grade made it worse than a 30 grade.
So Mobil's 5W20 (monograde, via their own blurbs and the papers of the time), with a 2.9 to 3.0 HTHS would have been protecting as well as a poor 10W40. the 0W, 5W, and 10W 40 grades had a 2.9HTHS minimum, just the same as the 30s up until recently.
M1 5W20 is not typical of the (clearly) CAFE driven 20s of today...nor of the 16s, which (clearly) have a single driver.