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Living the dream
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Discussion Starter #1
Yet another cooling system problem. I've searched the forum and found many cooling system problems and solutions but none seem to be exactly like the one I'm having. My cooling system is puking into the overflow tank but not sucking it back in when it cools. I'm using a 21# cap on the radiator and have plugged the bung. I'm using a 16# cap on the T-filler. I followed the recommended method for filling the system with the radiator cap off until it overflows and then putting the cap on the radiator and topping off the system. I've checked that my hose is connected to the correct tube on the overflow tank. I don’t think I have a leak in the system because when I take the T filler cap off once the system has cooled it makes a suction sound (like opening a new jar of Planters Peanuts). I even tested the cap by sucking on the check valve to make sure it would let air pass in. Any ideas?
 

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Living the dream
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Discussion Starter #3
Bad how? It seems to be sealing and it seems to be letting flow in.
 

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FFCobra Master Craftsman
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2,033 Posts
As the coolant heats up it expands and the cap lets it go to the overflow bottle (after 16 psi.). After the motor cools down the cap lets the coolant back into the system. Since you hear the sucking sound when you remove the cap I'm going to guess the cap isn't opening back up after cool down.
Jeff Hamilton
 

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Living the dream
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Discussion Starter #5
That's what I suspcte as weel. But when I tested it by sucking on it, it did allow flow back in that direction.
 

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Charter Member
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Worst case, you could be getting compressed air from cylinder into coolant. Run engine with cap off and look for bubbles. Some engines however will only open up small cracks when completly warmed up. Garages can test for these small cracks with specialized equipment.
 

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Jaime:
Is the 21# cap on the radiator hooked up to the overflow tank also? Or is the vent below the radiator cap plugged to prevent it from pulling air into the rad?
 

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Living the dream
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Discussion Starter #9
Yes, there is a vent in the overflow tank so it should allow the coolant to flow back into the system without restriction.

The vent bung on the radiator is plugged.

Like I said, the weird part is that when I open the system once it has cooled, it makes a poping sound like there is a vacuum in the system.

I only have two thouhts.
1. The hose that connect between the T filler and the catch can is about 24 inches higher at T filler connection than at the catch can connection. Coult it be that there is not enough vacuum being created by the cooling of the fluid in the system to counteract gravity.

2. The most logical explanation would be a bad cap that is not allowing flow back into the system, however I tested it by sucking on it and it let air pass. If I dont get any other ideas I may just test replacing the cap with a different one.
 

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Junior Charter Member
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One more..... I've seen the overflow tube collapse because someone used very thin, low pressure hose and when under vacuum, the hose collapsed and effectively isolated the overflow tank from the system.

Just something else for you to do on a Friday night.
 

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Member
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You could have a pin hole in the overflow tube. Did you ever try to suck through a straw with a hole in it?
 

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Living the dream
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Discussion Starter #13
Karl,

The cap has a one-way rubber flapper on the bottom of the spring laoded seal. When there is vacuum in the system this one-way valve allows coolant to pass through small holes located in the upper portion of the cap shaft. If you put your mouth around the bottom portion and suck on it, (this is the part where I start to wonder if you really wanted to know of if you just wanted to hear me describe this procedure in graphic detail) air should pass through it.
 

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Living the dream
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Discussion Starter #14
Jester,

Thats also a very good point, however the hose feeds from the bottom of my overflow tank.
 

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It sounds like the hose is plugged between the t-filler and the overflow tank,or like you said too far away for the vacuum to pull it.
 

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Senior Member
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Some puke tanks have a pressurised side and a open to air side. If you use the pressure side the system won't work very well. I would try it with a cheap bottle with the pipe just tied in so that it stays there, run the engine up to full temp (10 minutes or more) and then watch as it cools.....
 
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