#1  
Old 02-16-2021, 06:04 PM
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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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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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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.

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

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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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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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Old 02-28-2021, 09:03 PM
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An update.
I was working away for the last week and went to remove the radiator cap yesterday and there was still pressure behind it, to the point that some coolant sprayed out onto the inner fender and motor. That is after sitting for a week.
Also, the overflow tank is vented.

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Old 02-28-2021, 10:13 PM
shermanator2 shermanator2 is offline
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I am leaning toward something chemical going on here. If the cooling system had 16 PSI in it when at normal operating temperature, then cooled down to ambient temperature, the pressure would drop to below atmospheric pressure ant suck coolant from the overflow tank. I think the next step would be to drain and flush the cooling system and fill it with clean coolant and distilled water. It is scary to think that some chemical in your cooling system could be eating away metal. Maybe this has something to do with your water pump going bad. Did you completely drain the cooling system (including pulling both block plugs) when you changed the water pump? What do you guys down under put in your cooling system other than water?

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Old 02-28-2021, 10:36 PM
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I am using a mixture of 90% Ethylene Glycol and distilled water.

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Old 03-01-2021, 08:22 AM
gtospieg gtospieg is offline
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I thought the mix should be 50/50...

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Old 03-01-2021, 10:32 AM
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Yep I'd start with a 50/50 mix. Should actually cool better that way too. No telling what is happening chemically at that mixture. A 50/50 mix actually has about 35% more heat transfer abilities than pure anti-freeze, the freezing point is also lower with 50% water added.

Bear in mind, the water is not just there to dilute the antifreeze, there are chemical changes that take place in the Ethylene Glycol when mixed with water. Water produces vapor when heated that pressurizes the system, and condenses when the engine cools drawing down that pressure. Who know how pure anti-freeze behaves in the same cycle ... might expand and contract totally different than a 50/50 mix.

Almost sounds like there is somehow electrolysis taking place in the engine producing gasses. Is your battery by any chance going dead? Do you have any unusual electrical device attached to the engine? Maybe an electric temp gauge hooked up wrong that is shorting to the coolant or something of that nature?

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Old 03-01-2021, 11:50 AM
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I like the electrolysis idea.. I should have thought of that. I hope whatever is acting as the anode is not something important.

Here is another question. If after taking the cap off and relieving the pressure, you just put the cap back on without starting it and leave it over night, does the pressure build back up? If it does, then try the same thing with the battery disconnected.

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Old 03-01-2021, 03:23 PM
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Yep, when you think about it, a system with a recovery tank, radiator completely full of coolant would pressurize very quickly.

There is some guy on YouTube that makes electrolysis compressors ... they make thousands of PSI. I would guess on a car it would just relieve to the recovery tank now and then.

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Old 03-01-2021, 10:38 PM
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I just fitted a new OE radiator out of a Pontiac G8 to my car and run a factory 20psi cap. I went to open the cap the other morning when it was stone cold and it had pressure and spat a bit of coolant out. There shouldn't be any issue if it holds a small amount of pressure, your cap is doing its job.

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  #20  
Old 03-02-2021, 02:02 AM
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I totally agree with that, holding a couple PSI should be a non-issue.

If like Shermanator says .. it builds pressure after you take the cap off and put it back on ... then there is definitely something strange going on

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