radiator and over flow question
 

ok hope this doesnt make me sound stupid but i just havent figured this one out yet...if your radiator is under pressure how come it doesnt constantly blow out the overflow hose? as far as overflow bottles go ive seen every shape and size it seems...how does the water that goes into the overflow bottle get back into the system? im sure this is all 101 stuff, unfortunatly there are some things im barely at the 1 level...thanks

It's basic suckage & drawage - lessee if I can further confuse the issue. It doesn't blow out the overflow until the pressure rating of the cap is exceeded. With a sealed system, the radiator is always full, so with expansion when heated, some coolant will be forced out, and caught in the tank. As it cools it contracts, and if there is a sealed-system type cap in place, coolant will be sucked back into the radiator through the hose that ends near the bottom of the tank. Make any sense now? :)

so the bottom of the cap rests below the over flow opening until the pressure builds up and pushes cap bottom up and exposes the hole? wait, if the system cools and the cap goes back how does the coolent get back into the system if the hole is covered?

some of the over flow bottles ive seen are just that, bottles like a jim beam bottle or a beer can etc. i guess some people think those look cool...anyway all those will do is catch coolent and not let it get sucked back because its non pressurized? am i on the right track? lol sorry if im just being thick

CG, I'm very happy that you posted this, because I've been looking at mine trying to figure out the exact same thing. I just couldn't figure out how to word it without sounding like a total dufas.
I'm sure there are others who will need this info too.
Does your radiator have little square holes in the top?
I've been filling up my radiator every time I drive it for fear that the level will drop down too much.

http://www.mynrma.com.au/motoring/he.../cooling.shtml

You know, this internet stuff has answers for just about everything. :metal:

A) A cap designed for a sealed system will allow coolant to flow from the tank to the radiator when atmospheric pressure is greater than the pressure in the radiator - in other words, air pressure pushes it in as the radiator cools and is negatively pressurized.

B) Anything will work as an overflow tank; it's not pressurized. All you need is a hose that reaches near the bottom of the tank. Some of the OEM units have the hose connection at the bottom of the tank, so 100% of the coolant can be recovered, if necessary.

Does the recovery tank need to be at a certain height in relation to the top of the radiator or can you put it where ever it fits whether that is higher or lower than the top of the radiator?

I would think as long as the recovery tank is filled above the hose opening and the system is sealed it would work. Physics right? The system is going to suck something into the radiator to replace the lost coolant, if the hose is submerged in coolant inside the tank then coolant it will be. Shouldn't make much difference where the tank is should it?

[QUOTE=ACES]CG, I'm very happy that you posted this, because I've been looking at mine trying to figure out the exact same thing. I just couldn't figure out how to word it without sounding like a total dufas.
QUOTE]

no problem leave the dufassing to me :p

BtnkBndt has it right - it doesn't matter. However, since the radiator cap is usually atop the radiator, the tank will be lower. ;)

is your rad. overflow puking right now? dont over fill it when topping the level off.I keep mine about 1 to 2 inches below the fill opening. I dont have an overfill tank or bottle of any kind for my Big Block. never had any problems

After looking at Jeg's I think I am more confused than before. There are catch cans, recovery cans, and reciculating catch cans. I'd like a 'catch can' that will not only hold the "green puke" but also reintroduce the coolant to the radiator when the coolant temp. drops; and have a nice polished finish :D . I plan on mounting it between the gril and the radiator support on the radiator support. I'd be very happy if someone could look at Jeg's and tell me what it is I am looking for.

This takes place while the cap is still at it's relief pressure (open)? Most caps open at 15psi... I did a lil looking and normal atmospheric is 14.7psi. This seems to be throwin a wrench in the works! More explainin please... Better yet tell it like I'm a 4 year old. Maybe I can get my kid to help. (I'd throw a smiley in there but don't know how)

so, does that mean when the prerasure valve in the cap closes, and the "coolant" cools down there is a negative preasure, or in essence a vacume within the system?

Catch cans basically do just that. Catch the overflow and they usually have a means to drain like a petcock. You need a recirculating type can. There is not much difference between them all. Basically your system even though it has a cap and is closed is called a open system. The true closed system is used on all most all newer vehicles starting in about (guessing here) mid to late '90's. These systems have the tank mounted as high as the highest point of the cooling system to ensure that any air will not make a air lock. Sometimes the cap is on the recovery/expansion tank also. A lot of times the return out of the tank goes to a tee in the lower radiator hose. For your use just about any tank will work. It seems by looking at Jegs site even the different manufacturers interchange terms somewhat. If it has a drain, it's not what you want. Looking for one or two nipples for supply/return and vent and the "bling" is up to you. Looks like the Be-Cool, Jaz, Goza and Billet Specialties all have one for you.

Atmospheric pressure changes with altitude. That's good because I have "denser" air down here at sea level which means more power. The rating of the cap is at what pressure it opens (and that's how many pounds of pressure per square inch the cap is seeing). There is a spring that opens as pressure goes up which allows coolant to go out the nipple on the radiator. There is also a check valve that will open when pressure drops down (which creates a vacuum) and "suck" the coolant back in. Didn't think radiator caps had that many parts did you? :lol:

You only need one hose....as long as that hose is in the bottom of the bottle, it'll fill, and drain through that bottle.

if you had a 20 oz pop bottle with a hole the size of the hose in the cap and the hose going to the bottom of the bottle it would work. ask me how i know :D

A Mtn Dew bottle works, and the one liter size will pass tech at an NHRA track if properly secured. ;)

Yeah, I started answering for a open system and ended up answering for a closed type system (LS1 is always on my mind). :banghead: Edited post above.

i 'upgraded' to a castrol GTX quart bottle. it fits snuggly between the rad and the battery tray

But the one liter fits in the fender pocket nice if you pack some rags around it...and dew is way cooler than castrol. ;)

Yup - so depending on how you visualize it, either the vacuum within the system sucks the coolant out of the overflow tank, or - when atmospheric pressure exceeds the pressure within the system, it (atmospheric pressure) pushes the coolant back into the radiator. Same difference. :cool:

Not the same difference. Atmospheric pressure has nothing to do with it. As a liquid is heated it expands which creates pressure. We release the pressure via the cap to the tank. There is a seperate part of the cap with a return or check valve that is held closed by this pressure. As the system cools it shrinks which creates a vacuum which draws fluid from the tank. I am not following you logic about what atmospheric pressure has to do with it. When you put a tire pressure gauge on a empty tire what does it read? Zero, no pressure. With your line of reasoning I would have 14.7 psi in the tire. Explain to me how atmospheric pressure has something to do with this, I could be wrong, have been before (once in this thread already :D ) and will be again.

If I go with the 'Be Cool' recirculating catch can through Jeg's how are the lines hooked up?