1. If you have an original or replacement honeycomb radiator performing a flush / reverse flush is a good start.
2. Pull off the side cover plate on the drivers side of the block. The back of the block and the areas on the other side of the outside of the cylinder walls accumulate rust and debris and need pressurized water to clean them out properly. Get some stiff wire and form it so you can snake it behind the cylinder walls to encourage the accumulated material to dislodge.
3. Check the block side plate cover you removed for blockage and rust thru holes in the distribution plate that is on the inside. You should have a plate on the inside of the side cover plate that has multiple holes in it, each about 5/8" dia. These holes supply water from the water pump and direct it to the spaces between the cylinder walls and thru to the valve area. If this distribution plate is missing or has rusted out, the block is not going to be cooled properly.
I've cleaned out significant amounts of "sludge" in the back of these blocks by removing the side plate cover, even after performing reverse flushing. Reverse flushing will not generate enough flow to properly clean out the insides of the block. Worse, just reverse flushing loosens up material that ends up, you guessed it, in the passages of that nice clean reverse flushed radiator you just finished.
4. The following links show similar type distribution plates, different make and years from your car, but it will give you an idea of what to expect.
forums.aaca.org/topic/336684-plating-a-w ... acket/?tab=comments#comment-1961112forums.aaca.org/topic/362237-water-jacke ... nd-block-opinions-sought-31-auburn/ 5. I had an overheating issue on the same year /model as your car. Drove me crazy until I started looking closer at the Detroit Lubricator carburetor. My issue was running hot under intermediate to higher load. Under light load temp. would drop right down, speed didn't make much of a difference. The DL carburetors have a tendency to run lean if they are not set up properly or have worn parts. My issue was a lean mixture under intermediate to higher loads.
6. Other things to check, if the above doesn't help. Remove the water pump and use some clay to measure the gap between the pump impeller and the back of the block. To large of a gap and the water pump capacity will be reduced. Radiator hoses soft and collapsing, due to pump suction, and restricting flow. Check for correct ignition timing, retarded timing will cause overheating. Fan belt should be tight, loose belts will decrease pump flow.
Some other common cause of overheating:
rootesparts.com/id201.htm 7. A leaky water pump packing can sometimes allow air to get sucked in. I've had good results with graphite or teflon braided pump packing material, readily available from McMaster.
mcmaster.com/products/pump-packing/mcmaster.com/products/pump-packing/oil-and-water-resistant-packing-seals/ 8. A leaking head gasket or combustion gases leaking into the coolant can also cause overheating. Harbor Freight / Amazon / Auto Zone, etc. carry these. Easy to use and will detect a combustion leak.
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