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68s Big Blocks w/ overflow tanks ???

jims427400

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Vettehead Mikey

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None actually had expansion tanks- up to 1973 model year when 'everything' changed.

Basic rules of thumb-

1) No Corvette prior to 1973 had a true 'overflow' tank, but some had a pressurized surge or external expansion tank (two different names for the same barrel shaped aluminum tank on the inner fender well)

2) If the car originally had a radiator with a filler cap on it, there was no need for a surge or external expansion tank as there was provision for expansion of the coolant internally to the radiator. These radiators are usually brass/copper construction

3) If the original radiator had no filler cap, then a surge or external expansion tank was required. The radiator had no room for expansion internally as it ran 100% full all the time. These radiators are usually of aluminum construction.

4) It's a common mistake to run either configuration above filled to capacity as the excess coolant will puke on the ground shortly after shutdown. This puking is not a sign of malfunction, the system just needs a certain amount of air space for expansion.

5) In 1973 GM introduced a true coolant recovery tank system on the Corvette. This is the white plastic non-pressurized tank mounted on the right inner fender well. All cars had a radiator with a filler cap and were designed to be filled to the top. Once the coolant expanded and reached the set running pressure, the excess coolant was allowed to vent into the expansion tank. After shut down, the coolant was sucked back into the radiator. No puking.

The only thing that puzzles me is why it took GM so long to introduce this system as it's far superior to it's predecessors.

The trick is to determine which type of radiator is original and correct for your car. It varies quite a bit even within a given model year. :beer
 
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'67 Marina Blue Convertible
I asked this question about 2 yrs ago conserning my 67 tripower having an overflow tank and the concensus was never.
So now that I've been focusing on 68s, I've seen many w/ overflows. Am I crazy or did some 427s come equiped them.
Here's an example
http://cgi.ebay.com/ebaymotors/Chev...wItemQQcategoryZ6168QQitemZ120101252338QQrdZ1

That car has been "messed with" - it was built originally with a copper/brass radiator with side tanks and an integral cap, and no external expansion/supply tank.

:beer
 
Joined
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'67 Marina Blue Convertible
5) In 1973 GM introduced a true coolant recovery tank system on the Corvette. This is the white plastic non-pressurized tank mounted on the right inner fender well. All cars had a radiator with a filler cap and were designed to be filled to the top. Once the coolant expanded and reached the set running pressure, the excess coolant was allowed to vent into the expansion tank. After shut down, the coolant was sucked back into the radiator. No puking.

The only thing that puzzles me is why it took GM so long to introduce this system as it's far superior to it's predecessors.

The reason is that the Coolant Recovery System was already covered by a U.S. Patent by an independent inventor, and GM didn't want to pay the extreme royalty/licensing fees he demanded. Driven primarily by the overheat/puke/worse overheat cycle problems that led to head gasket failures on the '71-'72 Vega, GM went ahead and released the recovery system on '73 model cars anyway. The inventor then sued GM for patent infringement, and they settled with him out of court, gaining the right to use the system for a one-time cash settlement, with no ongoing royalties or licensing fees. Money talks. :)
 

jims427400

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JohnZ,
You mentioned "side tanks" does that mean they have built in overflow capabilities to cover the puke/overheat cycle?
 

Vettehead Mikey

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JohnZ,
You mentioned "side tanks" does that mean they have built in overflow capabilities to cover the puke/overheat cycle?

No- see rule of thumb 2) - internal room for expansion inside the radiator. And again, no Corvette prior to 1973 had an overflow tank of any type.

If filled to the correct level, and if all hardware is in good condition, there is no need for an overflow tank. The expanding coolant will compress the air inside the expansion chambers (side tanks on a copper/brass radiator) until max pressure rating of the cap is reached. If the pressure continues to rise and exceeds that rating, air is released at the radiator cap until the correct pressure is reestablished. If the system has been overfilled, coolant will be puked along with the air.

The most common instance of 'puking' is shortly after shutdown as the coolant in the block absorbs residual heat of the engine and achieves a temperature higher than while the engine is operating.

:beer
 
B

BRussell

Guest
My 68 is an original S/B, 4 speed with no air conditioning. It has the aluminum surge tank with an RC-26 15# cap. The radiator is copper/brass and appears to be from a B/B car. The radiator also has an RC-26 15# cap, and the overflow hose is connected to the surge tank. Surge tank overflow hose goes beneath the car as usual. I am having trouble getting all the air out of the system, and have come to believe that air is somehow drawn in thru the extra surge tank. Any thoughts or comments appreciated (sorry, didn't intend to hi-jack the thread) Thanks, Bob
 

Vettehead Mikey

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I am having trouble getting all the air out of the system, and have come to believe that air is somehow drawn in thru the extra surge tank.

You don't want to get rid of all the air, just enough that there's sufficient coolant to avoid overheating.

If your system is drawing in air, where is the coolant going?
 
Joined
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My 68 is an original S/B, 4 speed with no air conditioning. It has the aluminum surge tank with an RC-26 15# cap. The radiator is copper/brass and appears to be from a B/B car. The radiator also has an RC-26 15# cap, and the overflow hose is connected to the surge tank. Surge tank overflow hose goes beneath the car as usual. I am having trouble getting all the air out of the system, and have come to believe that air is somehow drawn in thru the extra surge tank. Any thoughts or comments appreciated (sorry, didn't intend to hi-jack the thread) Thanks, Bob

Your car was built originally with a stacked-plate Harrison aluminum radiator with no cap - just a tube that connected it to the inlet of the expansion/supply tank. The current setup you describe won't work as a "coolant recovery system". Can you post a photo of the tank and its connections?

:beer
 

jims427400

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67 427 tripower,68 427 tripower,04 Z16, 62 340hp
JohnZ
I guess I'm a little confussed. I've heard from different sources of both possibilities. With tank,w/out tank,alum.radiator,brass and copper..my car is very early production #320,maybe day 1, I dont know.
All I can say is it appears as to have never had to exp.tank, the 4 holes in the fenders are still plugged. And by the looks of my radiator, its looks original.But what do I know..
 

6880 Mike

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1968 convertible; 1980 L-82
JohnZ
I guess I'm a little confussed. I've heard from different sources of both possibilities. With tank,w/out tank,alum.radiator,brass and copper..my car is very early production #320,maybe day 1, I dont know.
All I can say is it appears as to have never had to exp.tank, the 4 holes in the fenders are still plugged. And by the looks of my radiator, its looks original.But what do I know..

Your car sounds as if it is correct. Radiator should be a big four-row copper/brass Harrison with a radiator cap. Your car did not/should not have a surge tank, as evidenced by the filled holes on the finder skirt.

Just curious, but what's the time/build date for #320? I'm guessing third day of production, but that's only a guess.

:)
 

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