Probably because they can make a heavier grade oil into a 10w-30 from group II stocks without using too much viscosity modifier. For the 5w-30 grade they probably need to add some more thermally stable Group III base stocks to get the viscosity index needed.
Probably because they can make a heavier grade oil into a 10w-30 from group II stocks without using too much viscosity modifier. For the 5w-30 grade they probably need to add some more thermally stable Group III base stocks to get the viscosity index needed.
That's one of the reasons why I use 5w30 HM blend instead of 10w30 HM conventional. I assume the 5w30 HM blend has better based oils, plus likely less wear at cold start.
I used 5w30 Maxlife Syn for a decade. It leaked a small puddle on concrete after each drive.
I switched to 5w30 Maxlife Blend (red bottle). Then it leaked only a few drops after each drive.
Then I had my valve cover gasket replaced. No more leak.
My car isn't an oil burner and only had a minor leak using Maxlife 5w30 HM blend (red bottle). Leak now fixed completely be replacing valve cover gasket.
If my car was an oil burner or a severe leaker, then I'd use a 10w30 HM conventional oil. Likely Pennzoil or Quaker State. Maybe Valvoline. And thicker the better (within grade) @ KV100.
As a last resort, I'd go up a grade in a HM oil. Ideally a conventional. 2nd choice a blend.
The spec sheet shows that 20w-50 has a viscosity index of just 126 so it is likely to be all or mostly all Group II or Group II+ base stocks. If there is any Group III included it will be a small fraction of the total.
The only Chevron oil I've seen in last 20 years said ISOSYN on the bottle, which an Oreilly store manager told me is Chevron's brand trademark name for synthetic blend. Am I missing something?