Technical Model A radiator

Okay here is my situation.


I have a model A with a 4 banger engine. I got one of these aluminum radiators for the build. ( shaved cap for a 32 grill shell). Had no issues until it got hot out. The car started puking it’s guts out through the over flow bottle.

Long story short , I have not touched the car in 3 weeks, went to check it out today and the upper hose had pressure in it. Opened the cap and got water all over the place.

1. How did pressure get in there ?

2. This aluminum job has a modern rad cap.

Should I switch to a zero psi cap? Or just get rid of this aluminum radiator ? ( I think I know what most will say )


I’m baffled how it got so much pressure with out driving the car , and how do I resolve this issue, while keeping my 32 filled grill shell ?

Thanks for any tips and pointers !

- Jon


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Got a photo of how your upper hose is routed?

 

I had a stock 29 Coupe which would do that when it got hot or on hill climbs and that ran a stock cap.
Turns out that the water pump had been replaced with repo replacement.
They look the same and fit in the same place up front on the engine, however the impellor design is such that it pumps the water thru the radiator way to quick and the water does not cool down in the radiator, so in hot weather or when extra heat was generated during a hill climb, it would boil and blow out all over my windshield.

I'm not sure if this is a part of your problem but it is worth knowing about.
I removed the pump and ground down the impellor vanes to match an original pump and then no more problems...

 

I think these new aluminum rads lets the water flow through to fast, you know no obstruction like an old half clogged radiator. That said maybe a 3 lb water cap and try that for a while. It’s only a few bucks if the problem still exists.

 

are you pumping compression into the water ? … gasket or cracked head/ block...

 

I don’t think that is the case, car sat for 3 weeks with out moving/ starting. No water in oil and cylinders dry.


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Best picture I have handy. The top hose was hard as a rock while the engine was cold.



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Hmmm, is there a thermostat involved anywhere?

 

Cooling systems build pressure because of expansion of the coolant due to increased temperature. Not because of the action of the water pump. Sounds to me like it is pumping compression into the cooling system due to a head gasket leak or cracked head.

 

How much room did you leave for coolant in the top of the tank when you filled it? Normally as soon as the engine and cooling system cools off the pressure drops off and unless it was sitting in the hot sun it shouldn't heat up enough to build pressure sitting.

 

Cylinders are dry and the head is Brand new. (Not saying that can’t be ruled out, but i have my doubts about it) oil does not show any water on the dip stick


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I topped it off to the top, I have not driven the car in 3 or so weeks, and it sits inside. I was shocked when there was pressure in there


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Z

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Well, there's not much else that will pressurize the system like that. System pressure that occurs due to expansion goes away when the system cools. The only thing that comes to mind that would force all the coolant out and then leave the cooling system pressurized is combustion pressure. Even then, for the system to hold pressure for 3 weeks is bizarre. You would think that wherever the combustion gases were entering the system would allow it to bleed off over 3 weeks time of not running. Strange....

 

If it is filled to the top with no air space it would take very little temperature rise to get positive pressure, the cap would let it go as high as 14 lbs before blowing. On the bright side it looks like your system is water tight.

 

Although this doesn't address the over heating when running problem.

 

After 3 weeks of not running whatever temperature rise there was would be gone. No?

 

A real 3 pipe puzzle.
Maybe get a sniffer to see if there is combustion stuff in the coolant. Like Blues said, it's like there is a high pressure leak from cylinder into the coolant but not large enough to push coolant into the combustion chamber. Copper head gasket?
That is a sweetie you got there. If there is something going on with a headgasket maybe when fixed it'll run cool as it should.

 

If it was filled with cold coolant and now the weather has been hot for the last few weeks?????

 

I doubt that kind of temperature change will build much pressure.

 

Man, you guys are making this way too hard, just go get a non pressure cap, Or, like I have, a seven pound cap, Let the rad find it's own level and drive the bag off it.

 

Does the radiator have an overflow tube? Or is it one of those that needs a pop off/pressure relief valve like Speedway's aluminum Model T hotrod radiators?
Most any car with pressure cap will hold pressure, sometimes for a very long time. I have pulled the cap off of some of my cars that have set for a month and still have a little pressure in it. Not so much it would hose ya down of course but they will hiss at ya.

Dave