Let me see if I can explain this to anyone. The expansion tank is for the overflow of the radiator. However it also connects to the heater core. 

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Your expansion tank is to handle coolant that expands as it heats up ... period ... that's it end of story . I have no idea why your putting it between the heater hose supply to the  heater core, those hoses connect directly to the heater core interrupted only by a heater control valve.

|UPDATED|3/24/2013 6:08:12 AM (AZT)|/UPDATED|


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1980 , ZZ430 , 3.92 rear , 700R4 2400 stall NEW EZ EFI 

Go back to April 5th 2012 under expansion tank forum. That is what I went by, so with that in mind what would be the purpose of the two outlets at the bottom of the expansion tank if they didn't go to the heater core?? 

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He's doing it like that because that's the way it's s'posed to be. The expansion tank goes in-line on one of the heater core hoses ...always has. I think the main question is, which hose to tie it into. I believe it should be in the hose coming from the intake fitting to the heater core. Since the two hoses are different sizes, the size of the fittings on the expansion tank should be a clue as to which section is used.

 In this other thread , Bob said he had info on how it goes. Perhaps he will share again.



Rich, if you are getting coolant out of the expansion tank onto the floor, perhaps your cap is not doing it's job? The air that is in the tank should keep the coolant from leaking out unless either the engine is running hot, and/or the cap is not holding a seal. You might try a new cap first.
Someone here HAS to have a '68-'69 AIM that would clear up this confusion... Anyone?


|UPDATED|3/24/2013 8:04:08 AM (AZT)|/UPDATED|


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Joel Adams
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My bad

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1980 , ZZ430 , 3.92 rear , 700R4 2400 stall NEW EZ EFI 

The larger hose the 3/4 is the only heater hose that fits the expansion tank. I have a new cap on the expansion tank. 

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Wow, I never realized those years had that.  My LT-1 just has an overflow hose to the ground. 

So why was it designed that way with the heater hose going through it?  Doesn't make sense to me.


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The design concept is similar to what you have in your water heater at home(or storage tank of a system with well water). There needs to be a space at the top that is nothing but air...a cushion of sorts. It also provides an amount of compression in the system. This is what keeps the tank from just filling all the way to the top with the engine running. As long as there is a specific, minimum amount of free air space in the tank, you should have NO leakage/spillage out of the tank under normal operating conditions. "Normal" meaning that the radiator does NOT also have a radiator cap on it, the cap on the expansion tank is holding the specified pressure, and the engine is not overheating. 

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Joel Adams
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These will help show how it is hooked up not sure it answers the question of operation will keep looking

Bob, thats interesting as they are marked 68-72 and 69-72. I have a 72 and dont have a tank like htat on mind. Does it just represent BB cars or maybe ones with AC? Mines a small block with no air. Hope it helps the original poster.
Rodney


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Supposedly, in '68, none of the big blocks had the expansion tank, even tho the L-88s did. In '69, SOME of the big blocks had one. I think it had to do with the radiator used for the specific engine. I think the engines with the aluminuminum radiators used the expansion tank, but not the copper radiators. Don't know for sure, tho...the info I have is confusing, at best.

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Joel Adams
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Now I understand, somewhat! 

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Here is some more info I found hopefully someone can add it all up and fill in some gaps

|UPDATED|3/28/2013 6:58:40 AM (AZT)|/UPDATED|

Hopefully I'm not being redundant, and more importantly I hope I'm accurate. The early Sharks had a pressurized expansion tank. The radiator and expansion tank caps were not vented as the later ones were, although I believe the expansion tank had a relief function. As water heats, it expands, and level rises in the expansion tank. Taking the cap off of the expansion tank is just like uncapping a hot radiator: it's under pressure, and will flash to steam if over 212F. The expansion line can be hooked up anywhere in the system, it really doesn't matter, as it's just additional volume for the system and keeps the radiator solid. The later ones (74 and up, I believe?) had a siphon/relief type coolant reservoir. Not technically an expansion tank. The radiator has a different type of cap: it both relieves on high pressure, and opens for reverse flow as the radiator cools (and the coolant subsequently contracts, forming a vacuum in the radiator). So excess water is displaced through the cap into the reservoir when it's hot, and sucked back into the radiator when it's cold. The reservoir is not under any pressure and is constantly vented to the atmosphere. Explains the "hot" and "cold" fluid levels on the reservoir. Two different ways of tackling the same problem: water expands when it gets hot. But in the later application, car makers don't have to worry about people burning themselves while checking coolant level. Earlier cars didn't have either one: you simply didn't fill the radiator up all the way. Fill it up too full, and it would relieve out onto the ground (someone mentioned an overflow line straight to the ground: that's it!). Hopefully I've gotten this right. Let me know if I've but out bad info, my skin isn't thin. :) Darryl

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"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner

Oh: one way to avoid the expansion tank is to install a catch can (vented). Change the radiator cap to a late model one, and buy a cheap expansion tank and run a hose to it. The hose has to go all the way to the bottom so it can siphon back in... I've seen hot rodders use a longneck beer bottle and a hose. It doesn't have to be high tech!

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"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner

I tried to update the applications if someone sees something wrong please correct

My unnerstanding is that combo will NOT work...as you have discovered. You cannot have two pressure caps in the system.
Bob...I've never seen the longer skinny surge tank...neat! Thanks for sharing that info, too!


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