.....and recently found that the 350 needs at least 4.5 - 5 gallons to stay cool, and my radiator now has a capacity of barely 2.5.
Would like to know where that number came from. My bone stock '98 C3500 7.4L only takes 2 gallons and some change.
I'd start with, what do you consider over heating? A '98 5.7L was designed to run at somewhere around 220 degrees all day long.
Last time I accidently put in a wrong rotation water pump, I ran cool at idle and saw the temp rise like crazy at highway speed.
