Somehow, I don't think paint was meant to be ran down tiny passages, even thinned out to the point where it's not paint. Hell, why is it so hard at times to get the air outta the radiator if it's so easy to get water into it?
).
But hey, don't let us sway you from trying to paint the inside of your radiator. When the paint dries and you clog it up because it's too thick and won't flow through it, be my guest. You obviously can afford another radiator if you're willing to do so. I wish you the best of luck in your endavour.
