Radiator Issue

Joel's explanation seems most plausible to me.

The hot/cold zones in the new radiator gives it away. Remember that a sprite pumps hot water OUT of the top of the head.......what else could explain a hot top and cold bottom? Jay
 
When you replaced the radiator, did you install new radiator hoses? If so, were the hoses packed in packing peanuts?
 
Mention of hoses reminded me:

Twice I've experienced a hose that "delaminated" and let the inner wall collapse with no indication on the outside. This chocked off all flow on the suction side. Hoses were very old, and on a Ford flathead, but may still be possible.

RJS
 
Ron, you have a lot of good suggestions to consider and I have another. I ran into a similar situation that ended being up a very small crack in the cylinder wall near the top of #1 at the front that would open up a little with heat and high rpm. This would over pressurize the cooling system and blow the coolant out. I could not find it by pressurizing the cooling system because it would not leak coolant into the cylinder. The high compression could get through it aerating (foam) the coolant which also reduced the cooling efficiency. It took me a long time to figure out the cause out the problem and I don't remember exactly how I found it.

Replacing the block resolved the problem for me. You may not have a problem with the block but I am sure a head or head gasket could also give similar results.
 
A real quick and simple check, if you have the type cap with the red release lever.

Let it run long enough to build a little heat, there should now be some pressure. Lift the little lever for a second or so, you should see some water / coolant enter the catch tank. Release the little red lever and the flow of coolant to the catch tank should stop.

This simple test will let you know the system is building at least a little pressure and if it does vent it will then re-seal.

If the cap is leaking it won't build pressure and won't re-seal.

Yes there are better ways of testing the system, with actual test equipment. But this simple test keeps all the parts where they will have to work.

Might need to use a system pressure tester to find some problems, also would be good to test the cap for the relief pressure. It should vent at about the pressure the cap is rated at, if not the cap could be bad. Or just try a different cap, they are fairly cheap, carry a spare.

With all winter to plan, what spares should we carry to the track??
 
Gary.... Have a still unrepaired Comptune head with a less than pin size hole in the #4 exhaust valve chamber that caused the same symptoms. Took forever to figure that one out. Not enough metal in that area to take the radical porting.

Bob
 
Before you remove head, fill sys. install coolant pressure tester.
Warm engine to operating temp, bleed pressure to 10 psi.
Rev engine and watch for pressure increase.
Blip throttle and watch for increase in pressure.
Cylinder pressure is around 10 times coolant pressure.
You should be able to tell if you have an internal pressure leak.
Never liked red lever caps. One more thing to fail, Woody
 
Thanks to all for the tips on trouble-shooting. The problem was a blockage in the radiator itself as a result of the relocation of the outlet tube. Joel wins the prize as his analysis was spot on.
 
Ron, I am pleased that you had a good weekend at Sebring for the Majors, and that I had the right diagnosis on the radiator problem. For what it's worth to anyone else reading this thread: the key was a sudden change in an otherwise good system, shortly after the installation of a new part - in this case, a new radiator that had a sudden internal failure. In these situations, the new part is always the most suspect...example:
I had a brother-in-law who raced an ITA Mazda RX-3 for a while. At one outing, it would start and idle okay but couldn't run on the track. I asked him, what have you done since the last race? "Nothing" Are you sure? Finally -"Well, I changed the fuel filter."
AHA! On the RX-3 the fuel filter was held in a bracket under the rear window/top of the trunk area, and had rubber hoses to/from it. The filter he bought did not fit in the supporting clip like the original, so he let it hang. When it filled with fuel, it sank down and pinched the inlet hose 'almost' shut. A couple of Ty-wraps secured it and relieved the problem.
The lesson is: when you change anything, be prepared for either the ripple-effect change (like that different fuel filter) or for the possibility of a new part failing early. In some work, early part failure is called "infant mortality"... Do watch for this. Joel
 
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