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post #21 of (permalink) Old 11-25-2012
Bobby B
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Joined: Jun 2010
Location: Long Island
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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.

Bobby B, a patriotic Long Island Senior Citizen who drives a 2011 5.0 Premium GT Coupe, all black, 6-speed MT82, 3.55:1 differential, Bama 87S Tune, 18" diameter wheels, Pirelli P-Zeros, Comfort & Security Packages, spoiler delete.
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