[donut]

I do something similar, esp with a "new to me" truck or if I'm tearing into the engine anyway. I'll add a qt of kerosene to the engine oil, warm it up, drain. I'll change it again fairly soon (or atf instead of kero, I've done both.) IIRC the "engine flush" you can buy at the major parts houses say the same thing.

Draining first doesn't sit well with me. In my mind, you still need the oil to flush the old nasties away.