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Radiator overflow tank


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I feel like this is a dumb question, but here goes... Have a '76 AMC Pacer, my first antique car new enough to have a plastic radiator overflow tank. What I don't understand is why it has "add" and "full" lines marked on the side. I see no return line to the radiator, so why does that range matter?  Can't see how the level would ever rise and fall and why the cap on top as if to add coolant? 

Jim
 

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These overflow tanks work by a hose as seen in your photo to an inlet usually just below the cap on the radiator just like most newer cars use.  The heat and cooling cycle of the engine pushes and pulls coolant from the tank.  When the engine is cold the coolant level should be close to the full mark on the tank.  If the coolant is instead at or below the add line then more coolant is required and you would put it in the tank up to the full line.  You did not add coolant to the radiator directly unless the cooling system was almost empty.

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Wow..., An AMC Pacer...!  I'd like to see some pictures of both the exterior and interior...

 

Keep in mind, that with an overflow tank setup, the radiator should be filled right to the point where the overflow hose attaches.

Of course, check this level when the engine is completely cold.  As soon as the warmed coolant expands, it will flow into the overflow tank.

The initial expansion will push the air out of the hose and into the tank. Once the coolant contracts, only liquid from the tank will be pulled

back into the radiator.  You can verify if the recovery system is working properly by checking the level in the tank when the engine is both

cold and hot.  The coolant level will be at the full mark when cold and above that mark when hot.

 

Also..., make sure the the radiator cap's big open center gasket which seals the cap to the mouth of the radiator is not missing or cracked. 

Although not under pressure, this gasket insures that the expanded coolant flows into the tank and prevents air from being sucked into the

radiator when the coolant contracts. 

 

Good Luck,

 

Paul

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Edited by pfloro (see edit history)
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Thanks to you both.  NOW I get it, I didn't see the hose going all the way down to the bottom of the overflow tank. That same hose flows both ways; overflow and suction back to the radiator.  The overflow tank IS where I add coolant. The question came about because I pulled out the radiator today due to a small leak and am going to bring it to my favorite rad repairman.  

 

As requested, a few photo's. It's a bare bones model, but nicely preserved. I'm going to see if someone somewhere can put in A/C. 

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A Pacer in any condition is unusual. More so one that looks nice and is roadworthy.

 

As usual, the independent was ahead of its time. Too advanced for the average American motorist (no pun intended).

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On 4/11/2021 at 5:23 PM, pfloro said:

Keep in mind, that with an overflow tank setup, the radiator should be filled right to the point where the overflow hose attaches.

The above is an important point! 

You mentioned that you have a radiator leak, in order for this design to work the cooling system must be FULL and leak free. 

 

Back when these systems were new I saw more that a few badly overheated cars. There was a cooling system leak but the owner never added coolant via the radiator cap they just kept filling the bottle. If there is any air in the system it can not suck in more liquid.  Eventually the bottle was full and the radiator was empty and the car was badly overheated. 

 

What you will learn is that the best place to check the accurate coolant level is under the cap. 

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That's good advice. Will make a point to check under the cap every so often. I'm getting a whole new core and he's beefing it up for more capacity than new.  Amazing, I found a recent youtube video of a radiator restoration on a '77 Pacer, I think it's called "on the road again".  Certainly perfect viewing for me at this moment. 

Jim

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The Pacer sold well for the first year or so, then its popularity tailed off. The idea was to build a car with the room and comfort of an intermediate, at least for the front seat passengers  which is all most cars carry 90% of the time. While being smaller and more economical than the typical intermediate car. It turned out this idea had limited appeal, most customers for smaller cars went the whole hog to small size 4 cylinder imports, Pintos and Vegas.

In their ads they called it 'the wide small car'.

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