1938 cadillac 346 v-8 losing antifreeze at overflow tube

[1938CADI007]

my 38-60 kepts losing  coolant at overflow tube. at idle when it warms up it is ok, but running at higher rpm or driving antifreeze comes out of the overflow tube.
if i take the cap off and race the engine the coolant is foamie.after driving about 5 miles it looses enought coolant to get on the hot side when i slow or stop.
i was told the the 38 uses a non pressure cap. that is what i'm using.i did a test to check to see if exhaust gases are getting in the radiator. and non are.
the shutter are wide open in front of the radiator. the car starts good hot or cold.
any help will be appreciated
jim

[Stinson]

Is an old hoses collapsing?
Ty Stinson
CLC22330

[Steve Passmore]

This seems like a classic case that I have seen many times before and have had happen to myself and not just on Cadillacs. The radiator is unable to keep the flow from the water pump circulating so a build up occurs in the header tank forcing water out the overflow.  Usally points to a blocked rad.

[Jim Stamper]

     In the opening statement in the 1937 Cadillac-LaSalle Shop Manual in the "Radiator" section,  a 4# pressure cap is described as the correct cap, which raises the boiling temperature a few degrees. This is not to say the problem isn't a plugged core or scaled core, collapsed hose or loose fanbelt or whatever. Since the shutters open it isn't that.

     Anyway, the book calls for a pressure cap. Does anyone ever go to a higher pressure cap to raise the boiling temperature more?

                                                                Jim Stamper CLC# 13470

[Jim Stamper]

     Jim;

     Forgot to mention, when you find a 4# cap, you have to make sure it is the right height in the pressure apparatus. The Cadillac radiator filler neck is a bit tall compared to later/other radiators, so if the sealing end of the cap doesn't reach the bottom of the neck, you still have an open system, and the fluid can still go right out the tube as it expands upon heating up. I use about a 1/4" slice of the size of a radiator hose that fits inside the neck to make a seal for a shorter cap. Just enough to come up just below the overflow hole. Under pressure, the spring moves and the fluid can escape. Seems to work OK, meanwhile I am looking for the correct depth cap.

     The book also says fill to 1" below the filler neck, to allow for a bit of expansion upon warming up.     Jim

[Bill Ingler #7799]

The proper cap for your car is an A/C cap RC-4 which is a 4# cap. A 4 # cap will add about 12 degrees to the boiling point so 224 at sea level. I have found each radiator will seek its own level of coolant. I have seen some radiatiors will stop expansion and carry the coolant just over the top of the tubes others just about 1/2 way on the upper tank. Does your radiator boil or are you just loosing coolant from expansion? I reccomend that you find out on your car what is the temp of the coolant when your dash gage reads 1/2, 3/4, or right on the H. Get a meat thermometer, block the shutters closed, run the engine and record the temp as it passes through the readings on the dash gage. Although the hottest part of your engine is the left rear where your temp sender is located, you still will get a fairly accurate reading from the top of the radiator. I have run both my cars right on the H and past without boiling. Both the sender and dash gage could be off so that is why I like to know what is close to the actual temp when I look at the dash gage.

[Edward Hurst]

Jim,

If the coolant is getting "foamy" you can pretty well bet that it is losing compression into the cooling system, most likely from a leaking head gasket.  When you look in the radiator do you see and brown stains?  This is a sure sign of a compression leak.

Ed

[John Washburn CLC 1067 Sadly deceased.]

The 37 and 38 had a long neck on the radiator to cap. The original caps had a seal at the bottom of the radiator neck, one would install a "O" ring to stop the fluid from going out the overflow. Seem to work for me, plus the old AC caps show this gasket.

Good luck

[Steve Passmore]

As Ed states, if the coolant is foaming it leads to a bigger problem than the Cap, and besides, unless Jim has recently changed his Cap, what type he has is academic.
How did you check that gases aren't getting into the rad Jim? A compression test would maybe tell if the head gasket was blown into a waterway, but its not always conclusive.
Steve

[Edward Hurst]

It's me again.    You can also put a pressure gauge on the neck and let the engine get hot to check the accumulated pressure, but don't pump up the tester.  Let the pressure build inside the radiator to check it with.  A slight bit of foaming is natural when it is rev'ed, but a good bit of foaming is not.  if you see any kind of rust stains in the radiator something is leaking somewhere.

Ed