radiator over flow tank
Thread Starter
Le Mans Master
Joined: Jul 2006
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From: charlotte north carolina
radiator over flow tank
it's back to work after a long weekend, and i'm going to ease into it by posting another dumb question.
how does an over flow tank work? the tube that goes to the radiator sits high in the tank, so it seems to me that air would get sucked back into the radiator rather than fluid. if the tube had an extension that feed to the bottom of the tank, fluid could flow back and forth between the two.
jeff
how does an over flow tank work? the tube that goes to the radiator sits high in the tank, so it seems to me that air would get sucked back into the radiator rather than fluid. if the tube had an extension that feed to the bottom of the tank, fluid could flow back and forth between the two.
jeff
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
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From: charlotte north carolina
overflow tank may have been an incorrect term, but the question remains the same, how does a pressurized expansion tank allow fluid to be drawn back into the radiator?
Le Mans Master
Joined: Jan 2006
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From: Boca Raton Florida
The tube from the radiator goes to the bottom of the overflow tank. When the pressure release cap vents, it will vent coolant and air into the tank. The tube end will be under the coolant so that when the radiator cools off and creates a vacuume inside, it will suck the liquid in the tank back in. If there is less liquid than the radiator vacuume can take, then yes, it will suck in air. The answer is to check the overflow tank when cold, if its dry, add a little coolant. When cold, there should be enough coolant in the tank to cover the bottom of the tube.
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
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From: charlotte north carolina
six
thanks for the reply. my question was prompted by my install of my tank yesterday. i noticed that the tube from the radiator did not have an extension that went to the bottom of the tank-it just stopped at the surface where it was welded to the tank. i couldn't understand how it was designed. i got my tank from ecklers. i'll give them a call.
jeff
thanks for the reply. my question was prompted by my install of my tank yesterday. i noticed that the tube from the radiator did not have an extension that went to the bottom of the tank-it just stopped at the surface where it was welded to the tank. i couldn't understand how it was designed. i got my tank from ecklers. i'll give them a call.
jeff
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
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From: charlotte north carolina
just got off the phone with ecklers. their tech said that the expansion tank feeds from the bottom, and overflow goes into the rad thru the small tube at the top. he also said that a vented rad cap will pass fluid in both directions-that's why a non-pressurized overflow tank will allow fluid to be drawn back into the rad. it makes sense, but i'm going to check it out when i get a chance.
jeff
jeff
Race Director
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I think you've been given a mixture of good and bad advice, especially by the guy from Ecklers. Most people don't understand how the two different systems work on pre '73 Corvettes.
If you have a radiator with a cap on it, you are not supposed to have an external expansion tank at all. Radiators with caps (pre '73) have internal expansion tanks. If they are overfilled or overheat, they puke on the ground.
If you have a radiator with NO cap on it (usually an aluminum rad) then the only place you should have a cap is on the separate expansion tank. Aluminum rads have no internal expansion tanks- which is why they need an external tank and all the extra plumbing. If they are overfilled or overheat, they puke on the ground.
Only '73 and up Corvettes have overflow tanks-usually plastic- that catch and return the overflow from the rad when it gets up to temperature. There are no internal or external expansion tanks, the rad gets filled 100% and the pukage gets caught by the overflow tank.
Trying to mix and match parts or technology from the two pre-73 systems with some post '73 system will cause confusion at the very least.
If you have a radiator with a cap on it, you are not supposed to have an external expansion tank at all. Radiators with caps (pre '73) have internal expansion tanks. If they are overfilled or overheat, they puke on the ground.
If you have a radiator with NO cap on it (usually an aluminum rad) then the only place you should have a cap is on the separate expansion tank. Aluminum rads have no internal expansion tanks- which is why they need an external tank and all the extra plumbing. If they are overfilled or overheat, they puke on the ground.
Only '73 and up Corvettes have overflow tanks-usually plastic- that catch and return the overflow from the rad when it gets up to temperature. There are no internal or external expansion tanks, the rad gets filled 100% and the pukage gets caught by the overflow tank.
Trying to mix and match parts or technology from the two pre-73 systems with some post '73 system will cause confusion at the very least.
Thread Starter
Le Mans Master
Joined: Jul 2006
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From: charlotte north carolina
mike
thanks for the reply. i've got a dewitts aluminium rad that has a cap, but as you said it doesn't have an internal expansion tank. hence, the external tank as per the 70 aim.
but i'm still confused about how the plumbing is supposed to work. the hook-ups are clearly shown in the aim, but what about the details? type of cap for the rad, how the fluid flows thru the small overflow hose, and in fact, why is there a small hose if the tank is feed from the bottom?
jeff
thanks for the reply. i've got a dewitts aluminium rad that has a cap, but as you said it doesn't have an internal expansion tank. hence, the external tank as per the 70 aim.
but i'm still confused about how the plumbing is supposed to work. the hook-ups are clearly shown in the aim, but what about the details? type of cap for the rad, how the fluid flows thru the small overflow hose, and in fact, why is there a small hose if the tank is feed from the bottom?
jeff
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Le Mans Master
Joined: Jan 2006
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From: Boca Raton Florida
Hey Jeff;
I don't think it matters much how the car was oroginally, if you have a regular radiator with a pressure cap and a vent nipple, the nipple should feed the overflow/expansion tank. It doesn't matter if it feeds in at the bottom of the tank, or in thru the top thru a hose to the bottom. The point being the opening to the feed/return line should be the lowest point to it is under water all the time. The regular 16psi pressure reliefe type rad cap will vent steam/coolant thru the cap and into the nipple when the pressure exceeds 16psi. Whatever comes out will follow the tube into the tank and keep the hose end covered. Once the radiator cools off and the coolant contracts it will create a vacuume in the radiator. There is a spring valve arrangement on the cap that will open to expose the vent hose to the vacuume in the radiator and it will suck the fluid back into the radiator until the tank is empty or the vacuume is relieved in the radiator.
I live in Boca and work in sunrise, be happy yo stop in sometime, see if I can help
I don't think it matters much how the car was oroginally, if you have a regular radiator with a pressure cap and a vent nipple, the nipple should feed the overflow/expansion tank. It doesn't matter if it feeds in at the bottom of the tank, or in thru the top thru a hose to the bottom. The point being the opening to the feed/return line should be the lowest point to it is under water all the time. The regular 16psi pressure reliefe type rad cap will vent steam/coolant thru the cap and into the nipple when the pressure exceeds 16psi. Whatever comes out will follow the tube into the tank and keep the hose end covered. Once the radiator cools off and the coolant contracts it will create a vacuume in the radiator. There is a spring valve arrangement on the cap that will open to expose the vent hose to the vacuume in the radiator and it will suck the fluid back into the radiator until the tank is empty or the vacuume is relieved in the radiator.
I live in Boca and work in sunrise, be happy yo stop in sometime, see if I can help
Race Director
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This may help you..l.this is my 78 "puke tank"....the little nipple on right feeds coolant back to rad when radiator cools....the bigger line on left at top of tank just vents to the atmosphere..(.no pressure cap..just a plastic one...)
I have a Dewitts rad with pressure cap/nipple...
This is my 69 (below)with NO Pressure cap on radiator...note hose routing on this system...the little hose off cap just vents to atmosphere...the other hose feeds from/to radiator...if overheating occurs,the pressure cap on tank will allow coolant to puke out on ground via the vent hose..
Note: The big line off bottom of tank connects to waterpump....
Rich
I have a Dewitts rad with pressure cap/nipple...
This is my 69 (below)with NO Pressure cap on radiator...note hose routing on this system...the little hose off cap just vents to atmosphere...the other hose feeds from/to radiator...if overheating occurs,the pressure cap on tank will allow coolant to puke out on ground via the vent hose..
Note: The big line off bottom of tank connects to waterpump....
Rich
Last edited by rihwoods; Sep 5, 2007 at 10:26 AM.
Race Director
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If the rad is correct for the car (and Tom DeWitt could confirm) then there is no need for an additional expansion tank. See my previous thread about the config of the two pre '73 systems.
Again assuming you've got the correct rad, you must leave a few inches of air space at the top when filling the system. This is the internal expansion space I referred to. If you fill it to the top (like a '73 and up system) then guaranteed you will puke coolant every time the engine is run, usually after shutdown.
Find out WHICH system your car is supposed to have and go from there NO Corvette has two radiator caps!
With all due respect, please ignore info on how post '73 cars are configured and operate. None of it applies to your car.
Melting Slicks
Joined: Jan 2006
Posts: 3,028
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From: North NJ
I was/am confused too.
Good post.
I have to confirm which radiator i have but it does have a nipple neck on the radiator to vent pressure and overflow. When I bought the car from Bubba there was just a hose from the radiator neck nipple to the ground. All my newer cars have overflow tanks so I thought the 68 should too.
I have been looking around for a tiny aftermarket overflow tank to suffice but now I must find out if my radiator has the internal expansion setup.
Do the GM radiators have part #'s? what are the tell tale signs of what radiator you have so you can identify it?
I don't see a problem in running an overflow tank with a vented top so if the radiator has extra fluid it goes into the tank and when it cools it sucks it back up. Will it hurt my radiator if it has an internal expansion and I put an overflow tank on it?
Good post.
I have to confirm which radiator i have but it does have a nipple neck on the radiator to vent pressure and overflow. When I bought the car from Bubba there was just a hose from the radiator neck nipple to the ground. All my newer cars have overflow tanks so I thought the 68 should too.
I have been looking around for a tiny aftermarket overflow tank to suffice but now I must find out if my radiator has the internal expansion setup.
Do the GM radiators have part #'s? what are the tell tale signs of what radiator you have so you can identify it?
I don't see a problem in running an overflow tank with a vented top so if the radiator has extra fluid it goes into the tank and when it cools it sucks it back up. Will it hurt my radiator if it has an internal expansion and I put an overflow tank on it?
Race Director
Joined: Mar 2006
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From: Florida
mike
thanks for the reply. i've got a dewitts aluminium rad that has a cap, but as you said it doesn't have an internal expansion tank. hence, the external tank as per the 70 aim.
but i'm still confused about how the plumbing is supposed to work. the hook-ups are clearly shown in the aim, but what about the details? type of cap for the rad, how the fluid flows thru the small overflow hose, and in fact, why is there a small hose if the tank is feed from the bottom?
jeff
thanks for the reply. i've got a dewitts aluminium rad that has a cap, but as you said it doesn't have an internal expansion tank. hence, the external tank as per the 70 aim.
but i'm still confused about how the plumbing is supposed to work. the hook-ups are clearly shown in the aim, but what about the details? type of cap for the rad, how the fluid flows thru the small overflow hose, and in fact, why is there a small hose if the tank is feed from the bottom?
jeff
This tank stuff is pretty straightforward.
Just work with what you have, unless you are going NCRS.
If the radiator has a pressure cap neck, Then it HAS built in tanks. (It is impossible to build a radiator and put a cap neck on the core alone).
This radiator with a pressure cap uses a overflow/recovery/puke tank, usually plastic.
If the radiator does NOT have the neck for the pressure cap, it may or may not have built in expansion tanks, but it does require the use of a remote expansion tank with a pressure cap. The coolant ciculates thru the remote expansion tank in a lower flow as plumbed in the aim manual.
See Rich's pics in his post above.
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
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From: charlotte north carolina
thanks for the replys.
rich, i have mine plumbed as you do. what cap do you have on your rad-vented or nonvented. i got a cheapo vented cap and cut the spring loaded vent plunger(or whatever it's called) off, so that the rad is sealed but the vent nipple is exposed. then i put a 15# vent cap on the expansion tank. the reason i did this was to allow free flow of the coolant thru the small nipple that is normally sealed by the vent plunger. i can see how it's all plumbed, but i just can't undersatand how the coolant is supposed to flow thru that small hose. with the 3/4" line connected to the bottom of the tank, just what in the heck is that smaller hose for? any pressure in the rad would vent off thru the 3/4 line and pop the vent in the tank cap. am i making too much of this????
thanks again
jeff
rich, i have mine plumbed as you do. what cap do you have on your rad-vented or nonvented. i got a cheapo vented cap and cut the spring loaded vent plunger(or whatever it's called) off, so that the rad is sealed but the vent nipple is exposed. then i put a 15# vent cap on the expansion tank. the reason i did this was to allow free flow of the coolant thru the small nipple that is normally sealed by the vent plunger. i can see how it's all plumbed, but i just can't undersatand how the coolant is supposed to flow thru that small hose. with the 3/4" line connected to the bottom of the tank, just what in the heck is that smaller hose for? any pressure in the rad would vent off thru the 3/4 line and pop the vent in the tank cap. am i making too much of this????
thanks again
jeff
Race Director
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thanks for the replys.
rich, i have mine plumbed as you do. what cap do you have on your rad-vented or nonvented. i got a cheapo vented cap and cut the spring loaded vent plunger(or whatever it's called) off, so that the rad is sealed but the vent nipple is exposed. then i put a 15# vent cap on the expansion tank. the reason i did this was to allow free flow of the coolant thru the small nipple that is normally sealed by the vent plunger. i can see how it's all plumbed, but i just can't undersatand how the coolant is supposed to flow thru that small hose. with the 3/4" line connected to the bottom of the tank, just what in the heck is that smaller hose for? any pressure in the rad would vent off thru the 3/4 line and pop the vent in the tank cap. am i making too much of this????
thanks again
jeff
rich, i have mine plumbed as you do. what cap do you have on your rad-vented or nonvented. i got a cheapo vented cap and cut the spring loaded vent plunger(or whatever it's called) off, so that the rad is sealed but the vent nipple is exposed. then i put a 15# vent cap on the expansion tank. the reason i did this was to allow free flow of the coolant thru the small nipple that is normally sealed by the vent plunger. i can see how it's all plumbed, but i just can't undersatand how the coolant is supposed to flow thru that small hose. with the 3/4" line connected to the bottom of the tank, just what in the heck is that smaller hose for? any pressure in the rad would vent off thru the 3/4 line and pop the vent in the tank cap. am i making too much of this????
thanks again
jeff
Now to your question...I think coolant flows back to the radiator as it cools via vacuum or siphon effect....(there may be a tube projecting into expansion tank off that nipple..) ???
On my 78 Dewiits,I have a non-vented pressure cap...same as stock one used for that year...
Since you have obviously invested in the metal expansion tank,maybe disabling the radiator pressure cap on radiator will allow this flow to occur....but risk is just over-pressuring the expasion tank and losing coolant off expansion tank pressure cap vent line(the small one)to atmosphere...
I don't recommend that....
If it were me,I would fit a plastic tank similiar to my 78...you can view these tanks at ZIP Corvette site for 73-77 vettes and would work with your Dewitts Rad pressure cap/nipple set-up..
Rich
Last edited by rihwoods; Sep 5, 2007 at 04:47 PM.
Former Vendor
Joined: Jan 2000
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From: Brighton
This tank stuff is pretty straightforward.
Just work with what you have, unless you are going NCRS.
If the radiator has a pressure cap neck, Then it HAS built in tanks. (It is impossible to build a radiator and put a cap neck on the core alone).
This radiator with a pressure cap uses a overflow/recovery/puke tank, usually plastic.
If the radiator does NOT have the neck for the pressure cap, it may or may not have built in expansion tanks, but it does require the use of a remote expansion tank with a pressure cap. The coolant ciculates thru the remote expansion tank in a lower flow as plumbed in the aim manual.
See Rich's pics in his post above.
Just work with what you have, unless you are going NCRS.
If the radiator has a pressure cap neck, Then it HAS built in tanks. (It is impossible to build a radiator and put a cap neck on the core alone).
This radiator with a pressure cap uses a overflow/recovery/puke tank, usually plastic.
If the radiator does NOT have the neck for the pressure cap, it may or may not have built in expansion tanks, but it does require the use of a remote expansion tank with a pressure cap. The coolant ciculates thru the remote expansion tank in a lower flow as plumbed in the aim manual.
See Rich's pics in his post above.
That's right. But this subject could go in many different directions because it isn't year/engine specific. I often see/hear people installing expansion (metal) tanks on cars that don't need them because they don't really understand the function. No car should ever have two caps on it but I see it all the time.
Thread Starter
Le Mans Master
Joined: Jul 2006
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From: charlotte north carolina
ok, i'm going to beat this dead horse one more time and then shoot it-the car, not the horse. rich mentioned a tube projecting into the tank. that's the original point that started this overly extended post. there isn't an extension, the small inlet on the tank ends flush with the inside of the tank. if it was designed to suction coolant back into the rad, it would only draw air. that means to me that the coolant flows only one way in the small hose-from the rad to the tank. i just couldn't understand how it was designed. i guess that i'll have to just plumb it as the aim, and accept the fact that the general's engineers are smarter than me!
jeff
jeff
Melting Slicks
Joined: Jan 2006
Posts: 3,028
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From: North NJ
ok, i'm going to beat this dead horse one more time and then shoot it-the car, not the horse. rich mentioned a tube projecting into the tank. that's the original point that started this overly extended post. there isn't an extension, the small inlet on the tank ends flush with the inside of the tank. if it was designed to suction coolant back into the rad, it would only draw air. that means to me that the coolant flows only one way in the small hose-from the rad to the tank. i just couldn't understand how it was designed. i guess that i'll have to just plumb it as the aim, and accept the fact that the general's engineers are smarter than me!
jeff
jeff
Pics would help end this "horses" suffering.
Does it look like the metal one in Rich's bottom pic?? that has a hose on top and a presurized cap so once that container is full it "pukes" the extra fluid out the top port, down the hose and onto the ground (which is why it doesn't need a pickup tube to the bottom of the container). The top port goes thru a hose to the pavement. The bottom port goes to the radiator. BUT as we've learned in this thread, this expansion tank is only for radiators that don't have a cap or no internal expansion tank. If your radiator has an internal expansion tank then just slap a hose on it to a plastic overflow container like in Rich's top pic. Thats what I'm doing. But make sure your radiator cap has the springs and such to open and close based on internal pressure.
Team Owner
Joined: Aug 1999
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From: Ontario
Here is an "expansion" tank. There is no provision for a cap on the aluminum rad. The cap on the tank is non-vented and pressurized at 16psi. The cold/full mark on the tank is 1/2 full. Is too much coolant is added there is a "puke" tube heading downward from the top of the tank to the ground.
