Originally Posted by bobs

If you're going to store the car for the winter, change the oil first! Moisture combines with combustion by-products in the oil and will form acids that will do nasty things to your motor.

Why would you want to run 15W50 in that engine? The mechanical tolerances are so close that it needs a thin oil to get lubrication everywhere. If you start running that pancake syrup sooner or later you're going to spin a bearing or score a cylinder and then your beautiful Crossfire will become a lawn ornament because you're not going to be able to afford a new engine and there's no way DC will honor the 7/70 powertrain warranty when they see you've been running the wrong oil.

Quit being cheap and use the oil that the engine designers told you to use.