Don't go above 5w-30. Based on all the info I have heard, the Duratec is a 'tight' engine, and the higher viscosity just adds more load and friction on the internals at startup.
Rob Weiss
'99 Mystique, 2.5L, MTX,Black/Tan, 37K miles
SVT Air Intake & Throttle Hang Plug
Build Date: December 14, 1998
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