Coolant flowing from radiator cap at speed

N

namvetmike

Junior Member
If I drive over 40mph coolant comes out at the radiator cap. The radiator is new with a qual radiator cap. Any suggestions on how I can fix this!


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Over filled radiator ,, should be at the level of the internal upper tank baffle

Bad seal on the cap

It should be coming out of the radiator overflow tube
 
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Very common of having the radiator filled too full. As long as the tubes are covered with water you will be fine. If you are adding water back up to full each time out you may never stop having water flow out of the radiator. Keep an eye on it and let it find the level that it likes. Use a meat thermometer placed in the water to make sure that it is not actually over heating. As Mitch said you should not have water coming out of the cap regardless. Any overflow should be out the tube at the bottom of the radiator. Your cap is not sealing.
 
Not to high jack this thread, but does the seal on the quail or on any other cap have anything to do with an over heating engine? Thanks.
 
No, since the standard system is not pressurized a leaky cap would have no affect on the cooling. Unless too much coolant leaks out of course.
 
You say the core is new. If it really is a new core, it will flow over 36 GPM. More than enough to handle whatever the pump can put out. Therefore, somehow you are getting gasses into the water jacket. If it's not steam, it has to be combustion gasses.
 
Service Bulletins discusses "bending" the overflow tube inside the radiator neck to make it less "in the flow" coming up from the motor. Overflow was a problem even "in the day."

Its possible to "add on" to this tube also using a short piece of Tygon tubing - and extend that overflow level up into the radiator cap (almost.)

Other solutions involve trimming down your water pump vanes (to reduce the quantity) or putting a "flow restrictor" (sold by the parts vendors) in the upper tube, or incorporating a thermostat (sold by the parts vendors.) Any of these will not make a sensible change to your motor temperature as the wide open flow is probably too high anyway. (and the biggest resistance to heat travel is at the copper tube/air juncture at the radiator exterior.)

As others have said, the Model A was designed such that as long as the tubes are covered by water at static level, there will be enough cooling.

Joe K
 
I had exactly the same problem. It turned out to be a cracked head. I also had tell-tale white smoke on start up from coolant leaking into a cylinder and burning.
 
I had that problem going up a steep hill near my house. Turned out that I checked the coolant level before we left, and I forgot to tighten the cap. I also have a quail and it is loose so i thought i had tighten the cap.

My wife was driving the car so I also suspect that she may not have adjusted the spark lever correctly going up the hill. I put a new seal just in case.

David Serrano
 
OK I'm going to highjack this thread a bit. I have the same problem on my speedster. Overflow at the cap at high revs/throttle. My first thought was a blown head gasket. This is a 100 mile motor, so anything is possible. I did a compression test and all across the board was an even 82 (B head skimmed). So my question. Is it possible it only leaks at higher pressures? I can do a leak down, but that's only 100 PSI or so. Should I assume the head's OK and start looking at all the other overflow ideas on this list? Remember, it spurts out the cap, not just dribbles out the overflow tube. Is there a better head gasket test?
Luckily, it is a speedster, so I catch the antifreeze with my face, thus saving the environment.
 
If you don't have a thermostat, I'd start there by installing one.

Also use a gasket that will seal the cap. Some guys have used a fat O-ring.
 
The cheap large HF Oring kits has one that fits nicely. They have 2 kits a metric (blue box) and a standard (red box) assortments. I believe the better fitting oring came from the metric kit..
 
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