My '07 Corolla has 5W-30 on the oil cap and in the owner's manual, but a TSB by Toyota says that 5W-20 is now preferred. I've got 5W-20 in it now...no problems.
I've recently started learning about HT/HS viscosity, and what it means. I generally understand the kinematic viscosity numbers, and understand that the shearing of oil reduces these viscosity numbers. Some oils appear to shear out of grade after so many thousands of miles. It appears that 5W-30 conventional oils are really at a 20W oil after a few thousand miles.
But does the HT/HS number lower also? I understand that the minimum HT/HS viscosity for 5W-20 and 5W-30 oils are 2.6 cP and 2.9 cP respectively. Figuring that I'll see absolutely no change in fuel economy between the two oil grades (I have not in our minivan), I reckon I'll use 5W-30 in it next time just for the better HT/HS viscosity. But if the 5W-30 oil shears down to a "5W-20" after a few thousand miles, do I lose the benefit of the higher HT/HS also? Does the HT/HS viscosity...well...lose viscosity as the miles pile on, as the kinematic viscosity tends to do?
Sorry if this has already been covered before...the search engine never seems to find what I'm looking for, even if I know I've read it here before.
Thanks.
I've recently started learning about HT/HS viscosity, and what it means. I generally understand the kinematic viscosity numbers, and understand that the shearing of oil reduces these viscosity numbers. Some oils appear to shear out of grade after so many thousands of miles. It appears that 5W-30 conventional oils are really at a 20W oil after a few thousand miles.
But does the HT/HS number lower also? I understand that the minimum HT/HS viscosity for 5W-20 and 5W-30 oils are 2.6 cP and 2.9 cP respectively. Figuring that I'll see absolutely no change in fuel economy between the two oil grades (I have not in our minivan), I reckon I'll use 5W-30 in it next time just for the better HT/HS viscosity. But if the 5W-30 oil shears down to a "5W-20" after a few thousand miles, do I lose the benefit of the higher HT/HS also? Does the HT/HS viscosity...well...lose viscosity as the miles pile on, as the kinematic viscosity tends to do?
Sorry if this has already been covered before...the search engine never seems to find what I'm looking for, even if I know I've read it here before.
Thanks.
