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Hot at the top of the radiator and cool at the bottom is real good, as long as you know the radiator is clean and flowing right. With the grill off (so you can get to the front of it) you should be able to feel it go gradually from hot at the top to cool at the bottom. Most likely, if it wasn't cleaned out well during a teardown, you've got crud and sediment in the head and in the water jacket around the sleeves. It can be all through, but it does tend to really pile up back around the rear of the engine and work forward, and it tends to be really dense stuff that doesn't break up easily. In both of mine it was solid up against the back of the water jacket, sloped down to where it still surrounded the sleeve of #4 about halfway up the front and continued forward to wrap right around #3 some, too. Bear in mind, that's a worst case. You can try flushing the system, with the radiator hooked up as a first step. Use about two pounds of Arm & Hammer Washing Soda(it's sodium carbonate, not bicarbonaate, and is usually next to the 20-Mule Team Borax in the grocery store) and mix (before filling) about three gallons of water (enough to fill) and take her out and give her a good hot run. Drain, refill with plain water, drain again and replace. Just keep in mind, the thermosiphon doesn't run fast enough to scour like a sytem with a waterpump does. If that doesn't fix it, you'll need to get more aggressive. You can take the hose off the upper engine outlet (the one the fan mounts to) and remove the lower inlet from the face of the block, and you should be able to get something with some pressure in there to knock the heavy stuff loose. (I THINK you can go straight in once the inlet is off -- somebody STOP ME NOW if that's not right!) I'd run water at plain old hose pressure down from the top to keep the crud flushing downward while getting a gentle pressure washer nozzle in the bottom, and directing the spray as far to the back as I could get it to go and keep it all running until she clears up some. You should get chunks. If you get to this point, you may have to get creative about getting a pressure nozzle in the bottom unless you remove the radiator -- maybe get a spare pipe for the PW wand and bend it??? but you have to really get back in there, so you may want to pull the radiator so you can go straight in. I'd follow this up with a flush with the washing soda as described above.
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