Radiator Overflow Recovery Tanks.

[Carnut]

Just call me dumb, I've never understood how overflow recovery tanks work, either OEM or aftermarket.

Can anyone enlighten me?

I've recently put a new aluminum crossflow radiator in my 61 Chrysler and have been wondering if I should also install an overflow recovery tank.

I understand how an overflow tank works. Stuff just spills out the overflow tube and drips on the ground, but how does the 'recovery' part work? I just don't understand how any 'suction' can occur with a 13lb radiator cap.

Does it take a special radiator cap? Or just a recovery tank setup with the two inlet and outlets on the bottom?

Do I even need one? I know NHRA requires them to keep the strip clean but If I don't care about dripping on the ground would a recovery tank even be worth the trouble and expense?

[39deluxe]

A standard radiator cap allows excess pressure to excape then reseals. The coolant goes out to the ground and when the system cools there is an air gap in the top of the radiator left by the expelled coolant.

A cap for a closed recovery system allows pressure to escape also but then allows the coolant to be drawn back in from the recovery tank as the systen cools. This keeps the radiator core full at all times. You must use a closed system cap with a recovery tank. One tube on the recovery tank connects to the radiator overflow and the other is just a vent to  the outside so the tank isn't pressurized and can flow freely.

Tom

[jaybee]

What he said.  With a coolant recovery system the rad will always be 100% full of coolant, with no air at the top.  Of course to do this your overflow hose has to go all the way to the bottom of your tank instead of just dumping in as it might with an overflow bottle.  It can either go in the top and extend all the way down or just be tapped into the bottom of the tank.  Every time the engine warms it'll push a small amount of coolant out into the tank, every time it cools it'll pull that same small amount back.

[river1]

is the only difference in the caps?

or does the rad have a "special" outlet the allows the cap to work?

later jim

[Bruce Dorsi]

is the only difference in the caps?

or does the rad have a "special" outlet the allows the cap to work?

later jim

There is nothing special about the radiator.  .....A coolant-recovery cap can replace a non-recovery cap, as long as it is the same size.  

Recovery caps are also available in various pressure ratings, but I have not personally seen any in a low pressure range, as required in some large-top tank radiators (such as 34 Ford).

[Rrumbler]

If you compare an old vertical flow radiator to a crossflow, you will see that the tanks on the vertical flow are rather large as compared to the side tanks on the crossflow, and the top tank, especially is about two to three times larger than the bottom tank.  We know that when the coolant gets hot it expands, and the top tank is the expansion tank in that style of radiator.  In the crossflow, there is need for an external expansion tank, thus the recovery bottle or tank; it just takes the place of that large top tank.

[jaybee]

I've fitted recovery tanks to any number of cars.  Just fit the right cap and an appropriate tank.  Seems like most of the time they hand me a cap that's set up for coolant recovery at the parts counter anyway, it's probably industry standard.

Regarding what Rrumbler said, I've noticed that cars with crossflow radiators tend to run just slightly cooler once fitted with coolant recovery when driven in hot weather with air on.  I assume that's because the entire core of the radiator is moving water at a slightly slower velocity instead of having the topmost rows of tubes filled with air.  Can't say it ever meant the difference between overheating or not, but it could in a car that has marginal cooling.

[Carnut]

Thanks guys for the education.

I've always been confused about the radiator cap part of the system. All radiator caps looked the same to me.

I did a search for coolant recover caps and found this pic



It shows that bottom valve for recovery that I've never paid attention to.

Guess I'll cogitate a bit on if I really want to do the entire recovery setup, but at least now I know what to pay attention to in radiator caps.

[river1]

yup, thanks for the education.

i had been pondering add a recovery system to the now sold 48.

good info to have for the future tho.

later jim

[junkyardjeff]

I think all the caps that the local discount parts store sell are designed for coolant recovery systems as I had to add the bottle to a couple of my old cars to keep from loosing coolant even with getting a cap the the computer said it called for,I might have filled the radiator too full but I like having a bottle on the cars.

[wayne petty]

a few thoughts..   the cap with the loose button.. thats not spring loaded.. is one i throw away when i run across them... i know there is a reason for it. but they don't build pressure until coolant flow pushes against the loose disc to close it..  

the caps i like have a spring to pull the disc against the rubber seal..

it works far better. as the increased pressure in the cooling system raises the boiling point of the coolant.

i have a copy of the stant radiator cap catalog.. all the conventional sized caps are coolant recovery type..


water and coolant expand when warmed...  this expansion has to go somewhere..   it gets pushed out through the cap when the pressure is above the rating..  and then when the system cools off after shut down.. it contracts and if you have springs in your hoses..   it pulls the coolant back in from the Bottom of the recovery bottle.. (thats where the hose connection should be..)


there are 98 options in not only overflow but remote pressure tanks from dorman through az...  most do NOT come with mounting brackets.. as those are attached to the car..

http://www.autozone.com/autozone/parts/Coolant-Recovery-Tank/_/N-8iilv?filterByKeyWord=coolant+recovery+tanks&fromString=search

[jaybee]

I particularly like this one.  http://www.autozone.com/autozone/parts/Dorman-Coolant-Recovery-Tank/_/N-8iilv?counter=23&filterByKeyWord=coolant+recovery+tanks&fromString=search&itemIdentifier=962698_0_0_  In addition to being reasonably priced it holds both radiator coolant and windshield washer fluid.

[t-vicky]

Just get an after market tank & bring it down & I will get you set-up.  Roger

[Carnut]

heh, heh, I just ordered a Trans Dapt tank online, I think I can get it in myself though.

thanks Roger.

[kb426]

I'm gonna go look at all my caps and see what I have.