Re: switching from mobil 1 to Royal Purple
With as tight as the clearances are on these motors there is a reason ford put 5/20 in them. My motor has been run on moble 1 since day one and it looked brand new inside when we pulled it apart (except for the headgasket) I'll never run anything but moble 1 in a modular motor.
Usually when you have black burnt oil built up it from lack of changing the oil.
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03 OW 5 speed 84k miles very clean. For sale!
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