Why would one use a motor oil with a higher viscosity than the manual specifies for street driving?
In my opinion, it is detrimental to do so because it takes more power to force a higher viscosity oil through the engine.
Since the oil pump is a positive displacement type, it takes more crankshaft power to run it with a higher viscosity oil.
The volume of oil flow through bearings and the filter decreases with a higher viscosity oil and the stock oil pump.
One could argue that a higher viscosity oil has better resistance to squeeze-out from bearings under high power loading. However, the Coyote Design Team made engine bearing design decisions predicated upon a 5W20 oil viscosity.
A higher viscosity oil is a consideration for an engine with a significant increase in torque and power resulting from supercharging or turbocharging.
Because Ford does that crap to advertise higer mpg. 5w20 is to thin for those cars. No one on here has ever had problems with 30 weight etc. At high rpms and highway 5w20 is to thin. Its like water drain it while its hot.
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