Difference between Expansion tank and recovery tank.
#1
Racer
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Difference between Expansion tank and recovery tank.
I just read an article in corvetteFAQ by Matt Gruber that said "do not confuse an expansion tank found in older vettes with a recovery tank. What exactly does each do? I figure as the glycol/water absorbs heat it expands and needs a place to go then returns as the rad cools. I thought this true of both. What then, are the differences of the two systems? And why do we need expansion tanks in c3's?
#5
Le Mans Master
Coolant expands as it is heated. When it expands, if your radiatior was filled to the max, where would the fluid go? On the ground. If you sent the coolant to a recovery tank, when the radiator collant cools it will go back into the radiator, keeping it full.
#8
Safety Car
Originally Posted by kend414
I just read an article in corvetteFAQ by Matt Gruber that said "do not confuse an expansion tank found in older vettes with a recovery tank. What exactly does each do? I figure as the glycol/water absorbs heat it expands and needs a place to go then returns as the rad cools. I thought this true of both. What then, are the differences of the two systems? And why do we need expansion tanks in c3's?
The expansion tank (described in the GM AIM as radiator supply tanks) also called surge tanks (a misnomer) as Gruber describes serves as an external supply tank also used to receive coolant. The radiators that accompanied the expansion tank had no means to receive coolant...the tube went directly from the radiator to the expansion tank. These radiators have no integal supply tanks like later C3s and typically are the aluminum radiators typically associated with high performance but not always. The exception are the A/C equipped big blocks.
C3s you'll recall are limited in space in which to plug in a radiator...it couldn't sit upright due to the low profile...so a radiator sized correctly was too big to stuff under the nose in the front...so the expansion tank was used...a carry over from C2. In C3 the problems were more pronounced and thus challenged with cooling requirements.
It was 1973 when the coolant recovery system was introduced and standardized for all Corvettes...all got the translucent coolant recovery tank.
So from 68-72 we see small blocks with an aluminum radiator and the surge tank...non A/C, manual transmission models. Other smallblocks with A/C got a brass radiator but no surge tank. We similar equipping of big blocks dependent on options but the key was the radiator type installed.
Oh...one last point! Those Corvettes with the traditional expansion tank just puked the coolant onto the pavement when overheating...these tanks did not serve the coolant recovery task of tanks from 73+.
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Originally Posted by kend414
Guess I just wondered why corvettes are the only cars that I know of that uses an expansion tank and not a recovery tank.
SOME C3s have recovery tanks, I think only the first couple of years of C3s had expansion tanks. My 76 has a recovery. I would guess it was 73 or 74 that got the first recovery tanks?
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Originally Posted by hunt4cleanair
Oh...one last point! Those Corvettes with the traditional expansion tank just puked the coolant onto the pavement when overheating...these tanks did not serve the coolant recovery task of tanks from 73+.
When the radiators with expansion tanks were properly filled (meaning the expansion tank is only about 1/4 full) here's how they work: the radiator heats up and the coolant expands. The excess coolant flows into the expansion tank. When the radiator cools back down, the coolant is drawn back into the radiator. The radiator essentially contains no air pockets. Unless there is a break in the system, there is no loss of coolant between changes.
With traditional radiators with coolant recovery tanks (overflow tanks) as the coolant expands and flows into the recovery tank, the fluid remains there and is never drawn back into the radiator. The top of the radiator is often empty (which is usually not a problem). Filling the radiator will only cause the excess coolant to go into the recovery tank as soon as the coolant expands. The primary reason for a recovery tank is to keep the coolant from spilling onto the pavement. Most race sanctioning bodies require recovery tanks for all liquids - oil, coolant, etc.
In 35 years of owning my Vette (including a couple of boilovers) I've never had coolant come out of the expansion tank overflow tube due to overheating. The only time this tube got moist was when I spilled coolant into it during filling. (If you were really retentive about it, you could add a recovery tank to your expansion tank.)
#14
Originally Posted by big_G
What are the proper radiator cap pressure ratings for the radiator and radiator supply tank?
15 lb.
15 lb.
#15
Le Mans Master
If you have the factory radiator and expansion tank, the radiator has no cap, only the expansion tank...............If you have overfilled the expansion tank, it will puke the excess, thats why it says "1/2 fill when cold"...lol
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Originally Posted by OldSchool
When using the radiator/surge tank (Harrison Aluminum Tank) Mounted on the fenderwell, the tank should have the pressure cap and the radiator should have what? Another pressure cap?
#17
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If you put a rad cap on the radiator and another on the expansion cap the system will run under the pressure of the 2 added together.
2 16 pound rad caps put the working pressure at 32 pounds.
I run a expansion tank and a overflow tank and found out the hard way that the pressure caps add to each other. I also monitor cooling system pressure.
This is my expansion tank. I have another behind the fender for overflow.
2 16 pound rad caps put the working pressure at 32 pounds.
I run a expansion tank and a overflow tank and found out the hard way that the pressure caps add to each other. I also monitor cooling system pressure.
This is my expansion tank. I have another behind the fender for overflow.
#18
Norval, explain please..how can 2 16 pund caps raise the operating pressure to 32 pounds? Both open @ 16 pounds because that's what the spring pressure is set at, @ 32 they'll both be open. When the 1st one opens to the expansiuon tank the system pressure drops till it euqalizes between the tank and the rest of the system, if you put even more heat in it and the pressure increases to rise it will open the 1st cap again till finally both the 1st and the 2nd one will open when the total system reaches 16 pounds again, with the larger volume (recovery tank added to cooling system)
Last edited by Twin_Turbo; 07-28-2005 at 01:28 PM.
#20
Originally Posted by hunt4cleanair
......serves as an external supply tank also used to receive coolant. The radiators that accompanied the expansion tank had no means to receive coolant....