#1  
Old 02-16-2021, 06:04 PM
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fbd73 fbd73 is offline
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Default Cooling system holding pressure

Hi All,
I have a 1973 Firebird Formula 350. About 3 years ago I installed a 3 core aluminium radiator from Ledfoot Racing. We also installed twin electric fans and have had no overheating or cooling issues since.
Now to the problem. A couple of weeks ago, I took the car out for an afternoon cruise. No problems. 24 hours later I went into the garage and noticed a pool of coolant on the garage floor. On inspection it was coming from the water pump. I went to take off the radiator cap and coolant sprayed all over the inner and outer fenders. The cooling system still had pressure after 24 hours. I have never heard of that happening. I have since replaced the water pump but the system holding pressure has not been solved.

What are your thoughts as to why this could have occurred?
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  #2  
Old 02-17-2021, 04:22 PM
gtospieg gtospieg is offline
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Is it possible you have a head gasket going bad and pumping presure into the system? I know it seems unlikely. I would think if it leaked in one direction it would "leak back" after shutdown....Unless the leak has to do with heat expansion that cools and stops the leak.

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Old 02-17-2021, 04:54 PM
shermanator2 shermanator2 is offline
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Radiator cap. There is nothing else that is supposed bleed pressure out of the cooling system. The situation you describe is very strange though. Normally when the car gets warm, the thermal expansion increases the pressure until the cap vents at 15psi or whatever it is set for, then as the engine cools the pressure drops back to atmospheric or below. Was it very cold overnight between your afternoon cruise and noticing the puddle and was it then warm? If so maybe nothing is wrong. What kind of radiator cap is that?

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Old 02-17-2021, 05:36 PM
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fbd73 fbd73 is offline
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We are in the middle of our summer here so definitely warm on the cruise and also overnight. Here is a photo of the radiator cap I purchased when I bought the radiator. Sorry for the bad photo.
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Old 02-21-2021, 06:02 PM
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fbd73 fbd73 is offline
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Here is an update. I put the new radiator cap on (16lb) and took it for a drive. All went well. I let the car cool down for about 4 hours and then went to remove the radiator cap. It was still holding pressure.

  #6  
Old 02-21-2021, 09:25 PM
shermanator2 shermanator2 is offline
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OK, for a long shot, what chemicals do you have in your coolant?

  #7  
Old 02-22-2021, 09:18 AM
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Another long shot ... clogged overflow tube? Does the position of the overflow fitting on the radiator require a specific cap to intersect the overflow tube fitting properly?

If the cap seal doesn't lift enough to uncover the overflow opening it might retain pressure.

Just mentioning it because the wild card here is the radiator. The design of the filler neck is pretty important to make the cap work properly. The spring in the cap has to be compressed the right amount etc.

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Old 02-22-2021, 11:53 PM
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fbd73 fbd73 is offline
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I checked the overflow tube and it isn't clogged. When I bought the radiator, I bought the radiator cap with it, so hopefully it was the correct one. It has been working well for nearly 3 years. It is a Champion Radiator 3 core aluminium radiator bought through Ledfoot Racing.

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Old 02-23-2021, 01:38 AM
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I'd drive it a few times with the new cap and see if it's doing the same thing after that. With no coolant recovery system the radiator has to find it's happy place. Expelling enough coolant till it has the proper amount of air space in the radiator. I know systems with no coolant recovery like the right amount of air space in the radiator, not sure if Champion makes any recommendations in that respect.

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Old 02-23-2021, 01:53 AM
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It does have an overflow bottle. One that I had custom made as shown in the photo.
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Old 02-23-2021, 09:39 AM
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Quote:
Originally Posted by fbd73 View Post
Here is an update. I put the new radiator cap on (16lb) and took it for a drive. All went well. I let the car cool down for about 4 hours and then went to remove the radiator cap. It was still holding pressure.
4 hrs cool down might not be enough.
Try letting it sit overnight with the new cap.
Is your recovery tank vented?

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