"PENNZOIL® SYNTHETIC MOTOR OIL is available in four viscosity grades, SAE 5W-20, SAE 5W-30, SAE 10W-30 and SAE 5W-50 and meets the requirements of API SL. The SAE 5W-20 surpasses the performance requirements of ILSAC GF-4, and Ford WSS M2C153-H and WSS M2C930-A specifications. Both the SAE 5W-30 and SAE 10W-30 surpass the performance requirements of ILSAC GF-4, GM 4718M, GM 6094M and API CF. SAE 5W-50 has been formulated to provide extra protection through a thicker oil film and does not provide fuel economy benefits like the other oils.
I don't see even a CF rating for 5w50 here... (although the 5W30 and 10W30 do have it), so I would avoid it...