Radiator confusion...need some advice
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
Originally Posted by big_G
I don't think so.....when the pressure reaches 7 lb., the cap will vent...Betcha....
Do any of you guys run a pressure gage?? Have you actually measured rad pressure??? Until you do don't assume anything.
I work in research and until you can varify anything don't believe it.
Le Mans Master
Joined: Apr 2000
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From: cincinnati ohio
St. Jude Donor '09
The only difference in my system as compared to the factory one is that I have a rad with a cap now instead of a closed one. How does this alter the way the system is pressurized???
Race Director
Joined: Nov 1999
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From: Foxfield CO 1970 Convertible
Originally Posted by yellow 72
The only difference in my system as compared to the factory one is that I have a rad with a cap now instead of a closed one. How does this alter the way the system is pressurized???
In a fluid system (ignoring gravity) the pressure on all sides of the system is identical. There is no "adding" of pressure caps. The lowest pressure cap will be the one that opens first. If there were ten 15# caps in various parts of the system and one 7# cap, the highest pressure the system could hold would be 7#. Of course, if your caps are non-functioning because of age or something else, they will open at an unpredictible time...
Le Mans Master
Joined: Jan 2006
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From: Boca Raton Florida
I think Norval is correct, the caps in series ADD together. In his case a 7lb cap on the rad will vent over 7 lbs, into the can which will vent over 7lbs. It will take 14lbs at the Rad to push 7 out of the can.
Race Director
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From: Waterloo ontario Canada
Originally Posted by SIXFOOTER
I think Norval is correct, the caps in series ADD together. In his case a 7lb cap on the rad will vent over 7 lbs, into the can which will vent over 7lbs. It will take 14lbs at the Rad to push 7 out of the can.
Race Director
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From: Foxfield CO 1970 Convertible
Originally Posted by SIXFOOTER
I think Norval is correct, the caps in series ADD together. In his case a 7lb cap on the rad will vent over 7 lbs, into the can which will vent over 7lbs. It will take 14lbs at the Rad to push 7 out of the can.
Another scenario: The can is not connected to the heater hose and the can was just a sealed can with a cap of its own. If the radiator suddenly went to say 10lbs, the radiator cap would pop at 7, and the pressure between the radiator and the can would rise to 10 (almost immediately), at which time the cap on the can would also open since it is a 7lb cap also. Within a fraction of a second, with the cap open, the pressure in the system returns to atmospheric and both caps snap shut.
Edit: in reality, this second scenario might result in both caps cycling at a rapid rate as the pressure is repeatedly raised and lowered between the two tanks and two caps. You'd probably get a weird sound ratcheting, hammering noise from the caps.
They *don't* add...if you have tested some sort of serial cap scenario, your testing methods, cap settings or something else is just wrong.
Last edited by Z-man; Feb 20, 2006 at 12:24 PM.
Race Director
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From: Waterloo ontario Canada
Z man have you tried it?? Theory is great but sometimes you actually have to try it.
This is a pressure container hooked directly to the intake, it sees full engine pressure. I have connected it to another exactly the same container under the fender lip. I have tried all sorts of configurations, I had 4 different caps to play with and notice the pressure gage on the side of the tank.
It adds the total of 2 7 pound caps when they are in series.
Try it yourself. I have many times.
This is a pressure container hooked directly to the intake, it sees full engine pressure. I have connected it to another exactly the same container under the fender lip. I have tried all sorts of configurations, I had 4 different caps to play with and notice the pressure gage on the side of the tank.
It adds the total of 2 7 pound caps when they are in series.
Try it yourself. I have many times.
Le Mans Master
Joined: Jan 2001
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I gutted a cap and put it on the radiator...
I then used a real pressure cap on the "pressurizer" cannister up near the fenderwell.
The gutted cap is nothing but a boundary for the coolant system now. Therefore my system works the same as the original radiator which did not have a filler/pressure cap.
The gutted cap is nothing but a boundary for the coolant system now. Therefore my system works the same as the original radiator which did not have a filler/pressure cap.
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Race Director
Joined: Nov 1999
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From: Foxfield CO 1970 Convertible
I must be missing some info. How is everyone testing these?
Something like this? (assumes two 7# caps):
- pump up system until engine pressure is 7# above atm.
- cap on radiator or main system opens (right?)
- gas/liquid flows to overflow tank
- at this time, engine pressure goes back below 7 because some of the liquid escapes to the overflow and lowers the pressure (right?)
- keep pumping until pressure in both engine and overflow increase above atm (pressure in engine and pressure in overflow might be 4# over atm. but should be about the same because they are connected by a hose, right?)
- keep pumping until pressure on overflow causes cap to open (both engine and overflow tank are at 7#, right?)
- cap on over flow is rated at 7# and opens at 7#, right?? (If it doesn't open, then it's not a 7# cap.)
Is this how the testing is done?
Something like this? (assumes two 7# caps):
- pump up system until engine pressure is 7# above atm.
- cap on radiator or main system opens (right?)
- gas/liquid flows to overflow tank
- at this time, engine pressure goes back below 7 because some of the liquid escapes to the overflow and lowers the pressure (right?)
- keep pumping until pressure in both engine and overflow increase above atm (pressure in engine and pressure in overflow might be 4# over atm. but should be about the same because they are connected by a hose, right?)
- keep pumping until pressure on overflow causes cap to open (both engine and overflow tank are at 7#, right?)
- cap on over flow is rated at 7# and opens at 7#, right?? (If it doesn't open, then it's not a 7# cap.)
Is this how the testing is done?
Le Mans Master
Joined: Apr 2000
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From: cincinnati ohio
St. Jude Donor '09
O.K. riddle me this guys......what's gunna' happen when I run a 27# cap on my radiator which I don't want to ever open (remember mine works just as the factory system except my radiator now has a cap) and a 13# on my expansion tank where I want pressure to escape if need be?
Race Director
Joined: Sep 2004
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by yellow 72
O.K. riddle me this guys......what's gunna' happen when I run a 27# cap on my radiator which I don't want to ever open (remember mine works just as the factory system except my radiator now has a cap) and a 13# on my expansion tank where I want pressure to escape if need be?
well not sure but i bet your radiator will blow up before any fluid is released......i say this because the cap has to release in order to discharge fluid to your overflow tank....i'd say you should go the other way and run a 1-2lbs cap so it automaticdally opens up and let the overflow control pressure, on mine the discharge tube is blocked until the cap vents
i suspected that what Norval is stating would happen to a small degree due to the increased volume of the second tank but never thought it would be doubled
Le Mans Master
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From: cincinnati ohio
St. Jude Donor '09
Originally Posted by bobs77vet
well not sure but i bet your radiator will blow up before any fluid is released......i say this because the cap has to release in order to discharge fluid to your overflow tank....i'd say you should go the other way and run a 1-2lbs cap so it automaticdally opens up and let the overflow control pressure, on mine the discharge tube is blocked until the cap vents
i suspected that what Norval is stating would happen to a small degree due to the increased volume of the second tank but never thought it would be doubled
i suspected that what Norval is stating would happen to a small degree due to the increased volume of the second tank but never thought it would be doubled
Race Director
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by yellow 72
I'm not using the radiator overflow, check the pics. My system operates the same as the original....
edit how does the water get to the over flow tank??? through the heater hoses???? if so you theory might be correct
Last edited by bobs77vet; Feb 20, 2006 at 08:25 PM.
Le Mans Master
Joined: Apr 2000
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From: cincinnati ohio
St. Jude Donor '09
Originally Posted by bobs77vet
sorry i must have misread/misinterpretted what you were asking
edit how does the water get to the over flow tank??? through the heater hoses???? if so you theory might be correct
edit how does the water get to the over flow tank??? through the heater hoses???? if so you theory might be correct
Former Vendor
Joined: Jan 2000
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From: Brighton
Originally Posted by norvalwilhelm
I know this sounds strange and I have trouble believing it but I run a pressure gage on my cooling system and I found when I had two 7 pound caps in series like in the picture you ADD the two caps together. A pair of 7 pound caps gave me 14 or 15 pounds of pressure. Without a gage you don't relize that a pair of 16 pound caps are actually making the system operate at 32 pounds.
The caps do add up if in series.
The caps do add up if in series.
This would be true, only if you did NOT connect the bottom tubes to the heater hoses and no other hoses are connected to the tank.
So the "vent" tube from cap A goes directly to the tank with another cap (B) on it. Cap B vent port goes to the floor. Then total cap pressure is A + B. If the tank is connected to the heater hoses, then cap B can blow independantly and pressure would be B only.
Former Vendor
Joined: Jan 2000
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From: Brighton
Originally Posted by Z-man
Like You said, the cap overflow is not sealed - it is open to the atmosphere. Any overflow may dribble out of it, but it will never get drawn back in, right? In fact, if you hook the cap overflow up to the expansion tank, the entire radiator system will be operating in a non-pressurized manner which defeats the purpose of pressurized caps. Your coolant will boil at a lower temperature.
No
Maybe
Yes--- the cap is vented to atmosphere
No--- most pressure caps WILL allow suck back. If you run the non-pressurize vent hose into an empty pepsi (or Coke) can it will suck the coolant back into the radiator when it cools down. That's how the 73-82's work.
Maybe---Again, everything depends on what the surge tank is connected to. It has four total connections. Two heater (3/4) connections, and one 3/8" tubes. These are all pressure ports. Then you have the filler neck vent.
Burning Brakes
Joined: Jul 2001
Posts: 853
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From: Foxfield, Co
OK I'll try. A #7 cap releases when it has a #7 differential from inlet to outlet. By having a second cap the 2nd one will charge up to 7lbs. So now the 1st cap has 7lbs on its outlet so it will build 14lbs on its inlet to get to its 7 lb rating. So now you have 14lbs in the radiator and 7lbs on the 2nd tank. 
Greg.
Greg.