finally found the 5w-20 TSB...

[Hershey]

may consider the 5w-20 when it's stamped on the oil cap .

[ibanezjeepguy]

have any of you actually hooked up a manual oil pressure gauge to the block to read during various loads and RPM speeds against one oil vs the other.
simple..... BOTH oils are rated to flow "like" a 5 during cold. its the operating temperature flow rating that changes. if the places the oil has to flow are tighter and/or more narrow passages then the 20 would be able to do that better, resulting it better protection. slightly thicker oil would technically mean more protection against thinning out under heat but is really the shearing forces more people should be concerned about instead of the flow ratings which is all viscosity ratings are really intended for. more people should be concerned with the other specs that manufacturers list on their websites and not necessarily on their products bottles. main difference people notice... fuel economy UP on the lower viscosity oil due to less effort for the oil pump to move around the fluid, and guess what drives the oil pump

[1stToyota]

I hear more about increased engine noise, and less about increased fuel economy...and with the info that's being passed around here about the possible oil leak at the head gasket I'll stick with the recommended thicker oil.

[frog13]

Originally Posted by Hershey

may consider the 5w-20 when it's stamped on the oil cap .

AND when they place the info in the manual......they test these vehicles over and over and over.....theres some BS somewhere...use whats in the manual or stamped on the oil cap....if something goes wrong,their responseable