saigonij
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| posted on 28/7/07 at 07:45 PM |
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expansion tank?
1) what have people used for an expansion tank???
i have a polo rad, and a zetec.
2) also, should the expansion tank be the highest item in the coolant plumbing?
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Michael
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| posted on 28/7/07 at 08:00 PM |
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Im thinking the same question, as using Xflow engine and xflow rad. Currently looking at Astra Expansion, but has over flow on bottle and bottom
outlet which i assume must come from Rad discharge pipe.
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robertst
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| posted on 28/7/07 at 08:17 PM |
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yes expansion tank should be at the highest point possible
the sierra one is what i'm using. its a bit big, but i dont really care. smaller ones can be obtained from old small cars (check the polo, it
might be useful)
Tom
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nitram38
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| posted on 28/7/07 at 09:11 PM |
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I bought a rover one from one of the MG range. As I have a rear engine, I lost water and did not know until gasket failure. The problem with rover
temp gauges is that once the water level drops, they read normal temps, so I carried on driving and cooked it.
The bottle I bought has a float switch and I have a light on the dash to let me know now!
Now I am building the MotaLeira, I have bought another one as this too has a rear engine.
Not cheap at nearly £40 from rover, but I am sure that there are some in the breakers.
The bottle comes with a 15mm bottom outlet and a top 6mm inlet.
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Confused but excited.
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| posted on 28/7/07 at 09:14 PM |
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Michael, look in Fozzie's pics, it's the nicest x-flow engine bay you are likely to see and has a really nice expansion/header tank
installed. 
If mine turns out looking anywhere near as good, I will be well chuffed. It's well thought out and superbly excecuted.
Tell them about the bent treacle edges!
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Peteff
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| posted on 28/7/07 at 10:45 PM |
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what have people used for an expansion tank???
I use a washing liquid bottle (don't ask, it was a temporary measure 3 years ago). An expansion tank is not a header tank, it runs off the
filler neck on my Mk2 Escort radiator and the pipe goes to the bottom of the tank so the coolant sucks back when the system cools down. You need the
proper cap for this to work.
[Edited on 28/7/07 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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nitram38
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| posted on 28/7/07 at 10:54 PM |
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quote:
Originally posted by Peteff
I use a washing liquid bottle (don't ask, it was a temporary measure 3 years ago). An expansion tank is not a header tank, it runs off the
filler neck on my Mk2 Escort radiator and the pipe goes to the bottom of the tank so the coolant sucks back when the system cools down. You need the
proper cap for this to work.
[Edited on 28/7/07 by Peteff]
Sometimes they are both, especially if they are the white nylon type.
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RazMan
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| posted on 29/7/07 at 08:04 AM |
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I have never quite grasped the expansion tank vs header tank thing.
I understand that if you have a pressurised cap on the header (like mine) then the overflow vents to atmosphere and any overflow (in the event of an
overheat) is lost.
With a non-pressurised system the same overflow feeds to an expansion tank and sucks any expansion water back when cold.
So does that simply mean that the pressurised system simply runs at a higher temp?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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nitram38
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| posted on 29/7/07 at 09:56 AM |
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Overflow bottles were "add ons" for existing old cars to help stop gradual water loss.
The modern solution was the expansion tank that became part of the system.
With a normal expansion tank, if you open the rad cap while hot (not a good idea) the water level will rise.
It is the pressure relief that allows the water to expand. Let it cool and the level will drop.
The main purpose of the modern expansion tank is to allow air to be removed from the system without water loss.
Get air in an old car system and the water epands and actually vents via the rad cap into the overflow bottle.
On cooling, the "shrinking" water in the engine creates a vacuum and pulls the water back into the system from the bottle.
Both work but a nylon type expansion system will be better long term as now modern cars never have water/anti freeze changes for years.
They are cleaner and more reliable.
As for pressure, the lower the pressure, the lower the boiling point. On Mount Everest water boils at around 65 degrees.
The opposite is true of pressurized systems, water boils at higher temps.
So you can run systems that hit 110-120 degrees without boiling over.
That is why you should not open a rad cap when hot.
As soon as you release the pressure and the water is over 100 degrees, then you get instand boiling.
[Edited on 29/7/2007 by nitram38]
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RazMan
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| posted on 29/7/07 at 10:21 AM |
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Yep, I understand most of that but my question was really regarding the reasons for choosing either system.
For example my header has a 15lb pressure cap fitted, therefore my boiling point is probably 120 degrees or so (disregarding any coolant additives) If
my system overheats any overflow is lost through the vent pipe (which leads to atmosphere) but in normal use everything seems to work fine with no
water loss - I just run the header tank half full to allow for expansion.
If I was to fit an expansion tank to the vent pipe the only advantage that I can see is that my water volume would be increased ..... or am I missing
something?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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nitram38
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| posted on 29/7/07 at 10:40 AM |
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If you added an overflow bottle to your system (not expansion tank as you already have one) then any coolant lost via the cap overflow would be drawn
back into the system on cooling.
Most modern expansion tanks do not have rad caps with overflow pipes and being made of nylon, expand more than closed metal types.
They do not need an overflow bottle as they hardly ever lose coolant unless something is wrong.
If you are leaving enough space in your header tank, then you shouldn't need to add anything to your system.
Remember what I said about overflow bottles? They were added to older cars without expansion tanks to minimise water loss, Older cars did not allow
for expansion or people overfilled them.
Here is another point:
If you leave space for expansion in an old engine then you can get overheating due to air in the system being drawn through the engine. Also not
allowing for some expansion, then you get water loss as the system vents it'self.
Unfortunately it will tend to vent more than it needs too and then the cycle of overheating will occur.
Fitting an expansion tank in the system bleeds air away from the Rad/engine to the highest point, while providing water with somewhere to expand to
when hot instead of venting to the atmospere.
The expansion bottle is the best way to go for any water cooled engine.
You seem to be getting overflow bottle and expansion tank confused.
They both work in different ways and provide different solutions to different problems.
[Edited on 29/7/2007 by nitram38]
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RazMan
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| posted on 29/7/07 at 01:00 PM |
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quote:
Originally posted by nitram38
You seem to be getting overflow bottle and expansion tank confused.
They both work in different ways and provide different solutions to different problems.
Ahhhhh it all becomes clearer now. I will put that down as 'the thing I learned today' 
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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