My 1931 coupe has to have coolant added about every 100-125 miles.

Is this a stock 31 coupe of an after market engine? If it is an after market engine, and you have a serpentine belt system, the radiator runs backwards. Check and make sure it is rotating in the correct direction. If it is stock, are all the holes for collect flow open and not blocked by the gaskets? How about the thermostat? Is it on upside right? Is it even working correctly? It would appear you have a blockage and causing the overflow to remove the built up coolant. Did you replace the radiator hoses? If they are old, they may be collapsing under pressure and restricting the flow of coolant.

It is a stock engine built in September 1930. The engine rotation is clockwise as viewed from the front. There is no thermostat in the circuit, and there is no blockage caused by any gaskets on the return. The hoses are new and note that this is an atmospheric pressure system.

If it is not a stock pump, just could it be pumping too much coolant through the radiator to coolant? Same as the newer engines that remove the thermostat and the coolant does not have time to cool down? Was the radiator repair/overhaul done correctly? Sometimes modern day equipment works too efficient for the older vehicles. It sounds from what you're tilling us, it is either a blockage issue or the coolant is not getting a chance to cool down. If you can employ a heat gun to find where the hottest part of the engine is, it may help pin pointing the problem. My grandpa, an old farmer, would just hit it with a hammer to fix it, but this may not be the case. Old cars may have used straight water and caused rust on the coolant journals, and now after years of care and driving, may of let go some and causing a blockage. Probably not the problem, but just guessing without looking. With no thermostat, my money would be on the rapid flow through the radiator and not allowing the coolant to cool down. Just a guess.

Is there anyway u can do a pressure check with top n bottom of lines also check radiator cap for cracked n seals never hurts ,start simple first

How much water are you putting in the radiator are you over filling also how hot is it running

This seems to be a very common problem. My 29, all original, stock, professionally restored model A, brand new radiator, stock water pump, also spews at higher rpms. Not overheating. This gets less, when my coolant level is lower. I am thinking of a sight gauge, as the top factory baffle prevents visable level of coolant. Then a motometer, to watch engine temp. If I run 30mph, never a slop. I know of a few other A's with the same simptoms.

Model A forums say that a restricted radiator will cause this problem. You may want to install a thermostat. Apparently there are 3 blade and 4 blade water pumps. A 3 blade pump may reduce the problem.

Forum. https://www.fordbarn.com/forum/showthread.php?t=149057&showall=1

i put a large headed nail in the overflow pipe, stopped the fluid loss and stays loose enough to still act as pressure relief.

I have the same problem with my 31 Coupe. I had H&H rebuild my motor and bought a new Radiator the Show Quality one from Bratton's and at speeds above 35 water trickles out the over flow pipe. What I found is this radiator is a JUNK design in the over flow pipe. On my 31 Roadster I put the $500 radiator on it. Never had any loss of fluid or over heat problem. The difference between the two on the $500 radiator the tube went all the way into the tank and up under the lip of the neck for the cap. The Show radiator from Bratton's the tube just stuck up in the middle of the tank. I did the rubber hose add on but didn't last more that a day or two of driving, so I pulled the radiator and had the over flow pipe re- routed like the $500 radiator and been working fine. John