Radiator running over
 

I have a 35 ford with a 37 flathead. New water pumps new core new thermostats. When the motor is cold thermostat is closed. Motor warms up thermostat open. I plugged the overflow tube and drilled and threaded a fitting in the radiator cap. Put a balloon on the fitting and started the motor. The balloon didn’t inflate so there isn’t any compression leak in the head gasket. Yesterday I went to a Route 66 cruise and when I stopped the car at different places the radiator would overflow out the tube. When I got home the antifreeze was down 2 gallons? Any ideas.

Re: Radiator running over
 

overheating? do you have temp gauge? one side may be overheating.

Re: Radiator running over
 

Gauge reads ok. I have only one gauge in the drivers side head.

Re: Radiator running over
 

can you see the tops of the radiator tubes? if so fill to there when the engine is warm, do not fill to there when the engine is cold. we have found thru trial and error with a 36 ford with a new brassworks radiator that it will thermosiphone more water out than is necessary to get to that point if you fill it cold. we measured the amount we put in and then ran it hard for 50 miles and it did not blow out any water and ran cool. we are running the hose thermostats/50% antifreeze/50 % water and two bottles of water wetter

Re: Radiator running over
 

Your just pumping water out the overflow tube. Put a plastic recovery
bottle on the left front frame horn and run a plastic or rubber hose from
the over flow tube to the bottle and see what happens. G.M.

Re: Radiator running over
 

Had the same issue with my 39, blowing water out every time I took it out. Wasn't overfilled and not getting hot. Running stats. Eventually replaced radiator cap and haven't had to add coolant since. I can only suggest that the coolant is backing up in the header tank.

Re: Radiator running over
 

Thank everyone for the come back. Will try new cap and install overflow tank. Will let you know the outcome!

Re: Radiator running over
 

rooster--- backing up in the tank-- just what we surmised

Re: Radiator running over
 

You didn't say if your new radiator has a pressure cap. A lot of pressure caps
don't hit and seal down on the washer like seat at the bottom of the filler neck. If it don't hit down on that seat before the underside of the top of the cap hits the top of the filler neck you don't have a working pressure cap I have had to put a rubber washer down on the bottom seat to make it work. 4 lb cap is
all you want. G.M.

Re: Radiator running over
 

no pressure cap. I ordered a new cap. The problem was the mixture of the antifreeze. I had too much antifreeze and not enough water. drained it out and replaced with 50/50 and now runs perfect. I thank everyone for the help.
Flatheads forever!!!!