133,000 miles
I'm planning on changing to synthetic oil (first time to my knowledge of this truck) today or tommorrow. I have one can of Seafoam kicking around and was wondering if I should dump some in the crankcase and go for a drive before changing the oil. How many miles (mountain driving) should I drive to give it a chance to work? Do I need to do this? Any precautions other than not using too much?
Thanks

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'95 T100 3.4L 4X4