SAE viscosity ratings in order of preference from best to worst:
The best possible: SAE 0W-60 (Very expensive)
The best available: SAE 5W-50 (Possible only with fully synthetic motor oil)
2nd best: SAE 5W-40 for colder climates (Synthetic or Blend)
SAE 10W-50 for warmer climates (Synthetic or Blend)
3rd best: SAE 5W-30 for colder climates
SAE 10W -40 for normal climates
SAE 20W-50 for hot climates
Average: SAE 10W-30
SAE 15W-40 for heavy duty diesel applications
Accepatable: SAE 30 for normal climates, but not in winter
SAE 40 for warmer climates, but not in winter
SAE 50 for hot climates, but not in winter
SAE 5W-20 for sub-zero temperature, winter use only
