Questions on Bleeding Coolant

[MidLifeCrisis]

I just fitted a new radiator and bled the system using the Simon Baxter method.
But I have a few questions that are still niggling me ......

1) When you reconnect the hose between the Header Tank and the Expansion Tank - the hose is full of air - does this matter - is there a way to pre-fill the hose somehow? Am I being overly fussy??

2) When you bleed at the radiator bleed screw - does this not lower the pressure in the system and therefore lead to the coolant boiling as it would no longer be under pressure (i.e. boiling point drops)? Or am I being overly fussy again??

3) Finally when the engines been run and cooled off - when I unscrew the Header Tank darlek there is a gargling/sucking sound like there is a pressure equalization going on and the Header Tank fluid level is down by about a couple of centimetres - I am assuming that the darlek is no longer working and not allowing fluid to be drawn back into the Header Tank from the expansion Tank - does that sound right?? Have a cap on order from Brickies just to be on safe side .....

....... Any thoughts?

[chapperss]

1. no does not matter, just fill up the resevoir tank.(just dont put any water in the expansion tank!)

2. the system is not pressurised it only expands as it heats up(hence the need for an expansion tank)then shrinks as cools down again.

3.sounds normal. mine does this. A guess here, but probably a bit of water moving about the system and shrinking back a bit more than when you filled it, causing a slight vacuum in the tank. but nothing to worry about.

[ghost123uk]

Non of the above is anything to worry about, and chappers is right, except when he says =

just dont put any water in the expansion tank!

I think he means it should be roughly filled to between the min and max marks

.

[Cruz]

2. the system is not pressurised it only expands as it heats up(hence the need for an expansion tank)then shrinks as cools down again.

Are you sure or do you want to phone a friend?

http://www.brick-yard.co.uk/forum/bleed ... 29710.html" onclick="window.open(this.href);return false;

The cooling system is meant to run at about 1 bar of pressure, thats about 15PSI in old money, that means that the coolant won't boil until about 115°c
So, the header tank is full to the brim, the cooling system reaches 1 bar and a valve opens in the cap and lets the excess pressurised coolant out into the expansion tank, the level in the one behind the flap rises.
once the engine cools, the coolant cools and contracts, if the system were to be totally sealed you would get rubber hoses collapsing, so inside the header tank cap is a second valve, a vacuum valve, this opens at some pressure or other (dunno that) and lets coolant from the expansion tank back into the header tank.
This keeps the header tank constantly topped up with coolant and no air in the system.

[chapperss]

Yes, much better explanation than mine!. forgot to say that as the system heats up and expands the pressure will build up too!

[MidLifeCrisis]

1) When you reconnect the hose between the Header Tank and the Expansion Tank - the hose is full of air - does this matter - is there a way to pre-fill the hose somehow? Am I being overly fussy??

OK then - to answer my own question 1) - I would think that as the coolant heats and expands and the dalek cap lets 'over pressure' coolant out into the header tank - that should push the air out of that hose; then when the coolant cools it will draw 'coolant' back into the system (rather than air) - so over a couple of hot/cold cycles it should almost 'burp' the air out of the Header tank.
Sound plausible?

[ghost123uk]

Yep, totally correct (except there shouldn't be any air in the header tank, but if there was, that is what would happen)

And chappers, I knew what you meant re heat and pressure

[California Dreamin]

1) When you reconnect the hose between the Header Tank and the Expansion Tank - the hose is full of air - does this matter - is there a way to pre-fill the hose somehow? Am I being overly fussy??

OK then - to answer my own question 1) - I would think that as the coolant heats and expands and the dalek cap lets 'over pressure' coolant out into the header tank - that should push the air out of that hose; then when the coolant cools it will draw 'coolant' back into the system (rather than air) - so over a couple of hot/cold cycles it should almost 'burp' the air out of the Header tank.
Sound plausible?

As John says, but air is very interesting in that it is extremely compressible and water/coolant isn't (think of SCUBA divers tank, where a 'whole room' of air is compressed into a small tank) .....So air doesn't 'draw' or 'push' coolant very well at all. Best keep bleeding & topping the main tank until it remains full.
Also....I have experienced several occasions where I have released coolant pressure and the coolant itself has 'instantly' started boiling. However, for the majority of the time the coolant remains several degrees below boiling point, somewhere between 85 & 95 degrees C.....having said this, it is possible to get 'localised' boiling, for example; when you have been driving hard then pull in and stop. releasing the pressure at this point could indeed lead to the coolant boiling as 'residual heat' around hot engine components super heats the now stagnant (none moving) coolant.

Martin

[California Dreamin]

I just fitted a new radiator and bled the system using the Simon Baxter method

Simon may have indeed written down a particular 'method' of bleeding cooling systems but I would hardly attribute this way of doing things to this one man.
We were bleeding cooling systems in much the same way back in the 80's when Simon was a weeeeee boy....no offence to Simon of course but I think I am right in saying he is relatively new to T25's/T3's (only been working on them for 10 years or so) lol.

Martin

[MidLifeCrisis]

I just fitted a new radiator and bled the system using the Simon Baxter method

Simon may have indeed written down a particular 'method' of bleeding cooling systems but I would hardly attribute this way of doing things to this one man.
We were bleeding cooling systems in much the same way back in the 80's when Simon was a weeeeee boy....no offence to Simon of course but I think I am right in saying he is relatively new to T25's/T3's (only been working on them for 10 years or so) lol.

Martin

Fair enuff - I just didn't think that "The bleeding method as linked in the Wiki section and titled 'Simon Baxter at brickwerks comprehensive how to bleed your van thread' " flowed quite as well ......

[California Dreamin]

Ner....I'm not having a go, the comment was definitely tongue in cheek (note only 10 years or so). Simon is an absolute godsend in terms of putting himself out there to re-produce many of vital but now obsolete parts for the T3, he definitely knows his T3's.
Without this man and his thriving business many of us would struggle to keep our old gals on the road.....and he does well out of it as he should.
And he did take the time to write-up this comprehensive methodology which has been useful to many.

But when I were spannering lol.......wooden pushrods owd lad

Martin

[Simon Baxter]

I just fitted a new radiator and bled the system using the Simon Baxter method.
But I have a few questions that are still niggling me ......

1) When you reconnect the hose between the Header Tank and the Expansion Tank - the hose is full of air - does this matter - is there a way to pre-fill the hose somehow? Am I being overly fussy??

2) When you bleed at the radiator bleed screw - does this not lower the pressure in the system and therefore lead to the coolant boiling as it would no longer be under pressure (i.e. boiling point drops)? Or am I being overly fussy again??

3) Finally when the engines been run and cooled off - when I unscrew the Header Tank darlek there is a gargling/sucking sound like there is a pressure equalization going on and the Header Tank fluid level is down by about a couple of centimetres - I am assuming that the darlek is no longer working and not allowing fluid to be drawn back into the Header Tank from the expansion Tank - does that sound right?? Have a cap on order from Brickies just to be on safe side .....

....... Any thoughts?

1. yes, too fussy. this air will make it's own way out in time. as the coolant warms and expands air and coolant will go down the tube to the burp tank, the pipe enters the tank at the bottom so any air just floats out leaving just coolant in. As the system cools it can pull only coolant back, not the air so the level in the burp tank will decrease over a couple of days while the last bits of air make their own way out. that's the reason i send customers vans out with that as high as possible, way above the max mark as when it settles it will drop to where it needs to be. It is of no detrement if that level in the burp tank is too high.
2. Yes, too fussy. it doesn't completely remove the pressure, just releases a bit of it. Cooling systems generally run about the 90° mark normally-ish, it shouldn't really boil.
3.In the cap there are 2 valves, one pressure, one negative pressure. The pfffft you hear is the pressure [or negative pressure] stored that wasn't great enough to open either of the valves, I wouldn't worry too much.

More on caps here.

More on bleeding here..

Very kind Martin.