slant 6 oil weight
Mixing in some 20w50 will bring the viscosity up a reasonable amount for engines that run hotter in the summer.
Switching from 10w30 to a 20w50 is a huge jump in viscosity and would not normally be needed. If the engine is that loose, or bearings that worn, then a 10w-40 in the winter is probably a better match.
If we focus on the oil viscosity when the engine is warmed up, for normal driving its temperature going to be in the same ballpark as the coolant and most of the block.
So lets say in winter that oil runs 180 to 212* F
Using Brad Penn 10w-30 as an example, those temperatures put the oil viscosity between 17 and 11 centiStoke.
If summertime oil temperatures are 195 to 220*F, then oil viscosity will range from 14 to 10 centiStoke.
Therefore if the viscosity that provides the best flow and bearing support is in the 10 to 18 centiStoke range, then 10W-30 will be fine all year around.
If we observe that in hot conditions the oil pressure is noticible lower, then mixing in some 20w-50 or switching to 10w-40 makes sense.
But the oil temps would have to be running much hotter before switching to 20w-50; Looking at the graph Brad's 20w-50 drops to 18 cSt around 220*F and does go below 10 cSt until 270* F.
Mixing in some 20w50 will bring the viscosity up a reasonable amount for engines that run hotter in the summer.
Switching from 10w30 to a 20w50 is a huge jump in viscosity and would not normally be needed. If the engine is that loose, or bearings that worn, then a 10w-40 in the winter is probably a better match.
If we focus on the oil viscosity when the engine is warmed up, for normal driving its temperature going to be in the same ballpark as the coolant and most of the block.
So lets say in winter that oil runs 180 to 212* F
Using Brad Penn 10w-30 as an example, those temperatures put the oil viscosity between 17 and 11 centiStoke.
If summertime oil temperatures are 195 to 220*F, then oil viscosity will range from 14 to 10 centiStoke.
Therefore if the viscosity that provides the best flow and bearing support is in the 10 to 18 centiStoke range, then 10W-30 will be fine all year around.
If we observe that in hot conditions the oil pressure is noticible lower, then mixing in some 20w-50 or switching to 10w-40 makes sense.
But the oil temps would have to be running much hotter before switching to 20w-50; Looking at the graph Brad's 20w-50 drops to 18 cSt around 220*F and does go below 10 cSt until 270* F.
