Outer Limits 4x4 Board

Hey all,

What does the radiator overflow do? and how does it work. I have heard some conflicting stories already

trying to diagnose a couple issues and making sure that this works first before i suspect other things.

edit: Is there a way to test it is working properly?

Thanks

when pressure builds up ion the radiator due to fluid expansion, it overrides the pressure relief spring in the cap, forcing coolant out of the cap into the coolant recovery bottle. Once the engine starts to cool down the coolant contracts. an increase in volume cause a decrease in pressure, atmospheric pressure pushing on the coolant in the recovery bottle then pushes the fluid back the recovery line, opening the recovery valve on the cap and keeping the radiator full.

If your cap is of the wrong type then it will not allow fluid to return to radiator. if it is not sealing correctly it will allow air to be pushed into the radiator and not coolant from the recovery bottle.

From what I understand, as coolant cools and contracts a slight vacum is created in the cooling system, sucking the coolant back into the radiator.
Most overflow bottles are below the radiator cap, atmospheric pressure is not going to push the coolant uphill through a little tube past a spring loaded valve

80's_delirious wrote:From what I understand, as coolant cools and contracts a slight vacum is created in the cooling system, sucking the coolant back into the radiator.
Most overflow bottles are below the radiator cap, atmospheric pressure is not going to push the coolant uphill through a little tube past a spring loaded valve

You would be amazed at how powerful atmospheric pressure can be!

chimpboy wrote:

80's_delirious wrote:From what I understand, as coolant cools and contracts a slight vacum is created in the cooling system, sucking the coolant back into the radiator.
Most overflow bottles are below the radiator cap, atmospheric pressure is not going to push the coolant uphill through a little tube past a spring loaded valve

You would be amazed at how powerful atmospheric pressure can be!

so if I put a hose into the top af a bucket of water, atmospheric pressure will let me water the garden right


i think gravity outweighs atmospheric pressure at anything near sea level.

80's_delirious wrote:

chimpboy wrote:

80's_delirious wrote:From what I understand, as coolant cools and contracts a slight vacum is created in the cooling system, sucking the coolant back into the radiator.
Most overflow bottles are below the radiator cap, atmospheric pressure is not going to push the coolant uphill through a little tube past a spring loaded valve

You would be amazed at how powerful atmospheric pressure can be!

so if I put a hose into the top af a bucket of water, atmospheric pressure will let me water the garden right


i think gravity outweighs atmospheric pressure at anything near sea level.

80's is spoton on this one , a vaccum is created sucking the coolant back in.

You are right in that you have a vacuum of sorts but it does not suck the water back in. It is the 14.7psi (approximately) of atmospheric pressure that pushes it back into the radiator.

it is the same principle as all pumps. an increase in volume cause a decrease in pressure. atmospheric pressure which is 14.7 psi then pushes fluid or air to fill the void.

80's_delirious wrote:

chimpboy wrote:

80's_delirious wrote:From what I understand, as coolant cools and contracts a slight vacum is created in the cooling system, sucking the coolant back into the radiator.
Most overflow bottles are below the radiator cap, atmospheric pressure is not going to push the coolant uphill through a little tube past a spring loaded valve

You would be amazed at how powerful atmospheric pressure can be!

so if I put a hose into the top af a bucket of water, atmospheric pressure will let me water the garden right

If you can get the other end of that hose to be a bit under atmospheric pressure, then my word the water will go scooting uphill.

That is exactly how you get your coke to go uphill when you drink through a straw. We think of it as "sucking" because we are used to having atmospheric pressure all around us all the time, but strictly speaking it's the atmospheric pressure doing the pushing.

In that case, I have something you can "push" on then...

lump_a_charcoal wrote:In that case, I have something you can "push" on then...

I can hear it now!

(highly pleasured voice) "ohhh, . . . mmm . . . , baby, youve just about got the end of my "hose" below atmospheric pressure"

Righto fellers, i have a quick question.

I'm trying to work out where i'm going to relocate my dual battery tray and overflow/recovery bottle in my GQ. The main issue i have is the stupid ARB tray forms around the overflow bottle, and uses the overflow bottle bolts to mount up. Move one, and i must move the other.

To make this simple, i was thinking of putting a small (tall and skinny) overflow/recovery bottle between my airbox and the radiator support, which would give me HEAPS of room for the dual battery setup.

Something like this:


Or possibly smaller.

What are the implications of altering the height of one of these bottles? I read that you have to be careful when relocating recovery type bottles as they are under pressure - this is what mine is (screw top, two hoses in it).

Any help/info would be great!

Cheers

I think you're getting conflicting explanations because there are basically two kinds of bottle you're likely to find in a car. One kind is fully pressurised and has a proper radiator-type pressure cap on it. It is more like an extension of the radiator except that it is effectively self-bleeding.

The other kind is an overflow bottle that is "outside" the pressurised system; when the system starts to exceed the cap pressure rating coolant passes outside the cap, through a small hose, and into the overflow bottle. Then when the system cools and pressure drops, it draws fluid back past the pressure cap. But the bottle itself is not actually pressurised and has no reason to be.

Well, those are the kinds I've seen anyway.

In both cases if the system is sealed properly (and it has to be or you're stuffed), the height shouldn't really matter but you'd probably want to just keep it within spitting distance of the radiator cap height. THe important thing is that the return line has to pick up coolant from the bottom of the bottle either by having a pipe poking downward from the top or by having the recovery hole at the bottom.

chimpboy wrote:I think you're getting conflicting explanations because there are basically two kinds of bottle you're likely to find in a car. One kind is fully pressurised and has a proper radiator-type pressure cap on it. It is more like an extension of the radiator except that it is effectively self-bleeding.

Righto - now that you mentioned "proper" radiator caps, a Falcon setup comes straight to mind.

chimpboy wrote:The other kind is an overflow bottle that is "outside" the pressurised system; when the system starts to exceed the cap pressure rating coolant passes outside the cap, through a small hose, and into the overflow bottle. Then when the system cools and pressure drops, it draws fluid back past the pressure cap. But the bottle itself is not actually pressurised and has no reason to be.

Well, those are the kinds I've seen anyway.

In both cases if the system is sealed properly (and it has to be or you're stuffed), the height shouldn't really matter but you'd probably want to just keep it within spitting distance of the radiator cap height. THe important thing is that the return line has to pick up coolant from the bottom of the bottle either by having a pipe poking downward from the top or by having the recovery hole at the bottom.

Sweet. I was going to get something as i pictured above, and then either plump a fitting for the pickup point to be at the base of the tank, or to run a drop hose that has the pickup at the very base of the tank.

Much like you said, provided the return/pickup hose end-point always has coolant available and doesn't suck air - it'll be ok.

Thanks chimpy.