1979 400 overheating drama solved?
 

So, got the truck from my dad, 1979 f250 4x4, always ran hot, blew the top tank, replaced hoses, replaced radiator, replaced 3 stats, 180 and 192 etc. was dragging ass on changing water pump, ran it with 1 gallon of CLR for a day, ran it full of calgon for 2 days, flushed this thing 9 times in 2 years. Nothing! Flex fan, then fan clutch. Timing, carbs, nothing. Always overheats, moving, not moving, highway, standing. So, finally in traffic, blows the top hose off and a ton of what looks like wadding comes out, like never dull pad. Great, unclogged? No! Overheats still. So, frustrated, I fill it with a bottle of Lemishine, the dish washing additive. It's used to clean dishwashers. The stuff stays in for 40 mins, turns green. I flush it out. No more overheating. Gets a little over temp 65 due to fan / shroud / weirdness. I suspect no fender wells adds to air bubble or whatever. Go figure. Fighting this for 2 years, and a bottle of Lemishine? What the hell? This is radiator number 3 and the smallest if the 3. Maybe block was lined with something? Lets see how many days it stays fixed.

Are you sure you don't have a leaking head gasket? How does the oil look?

I have to ask, where did you get the thermostats?

Sounds like your water jacket is clogged up, plus a corroded water pump.

I second this. Lol. Seems silly but 335 series takes a different thermostat.

Thermostats
 

The thermostats have been from oreilly's, they have the flanged skirt on on the pellet.