Barksavon
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| posted on 14/10/10 at 08:58 PM |
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Header Tank / Expansion Tank
I want to get rid of the large plastic expansion tank on my Pinto powered Tiger Avon and replace it with a smaller smarter aluminium one. The ones ive
looked at are advertised as header tanks with an outlet, an inlet and an overflow outlet fitted in the neck just under the cap. My plastic tank has an
outlet at the bottom to the bottom of the rad and a return running from the small outlet on the thermostat housing (doesnt have an overflow outlet) Is
there a difference between expansion tanks and header tanks and can i replace my plastic one with an aly 'header' tank
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blakep82
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| posted on 14/10/10 at 09:24 PM |
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as i understand it...
header tank, hold water, has a inlet from the thermostat housing, and an outlet to the bottom hose, and has a pressure cap on the tank
expansion tank is one where off the filler neck below the pressure cap (on a radiator for example) there's an outlet which goes to a bottlewhich
has water in it, when the water in the system expands it goes into the bottle, and when the system cool, it sucks water back in, the the bottle itself
is not under pressure
i think... i get confused. everyone seems to call them all the same names lol
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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britishtrident
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| posted on 15/10/10 at 10:21 AM |
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Normally on modern tanks the overflow is in the cap itself.
If you want a small tank the small tank from the bubble shape Rover 200/25 tank (nb not 400/45) is the way to go.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Strontium Dog
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| posted on 15/10/10 at 10:29 AM |
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quote:
Originally posted by blakep82
as i understand it...
header tank, hold water, has a inlet from the thermostat housing, and an outlet to the bottom hose, and has a pressure cap on the tank
expansion tank is one where off the filler neck below the pressure cap (on a radiator for example) there's an outlet which goes to a bottle
which has water in it, when the water in the system expands it goes into the bottle, and when the system cool, it sucks water back in, the the bottle
itself is not under pressure
i think... i get confused. everyone seems to call them all the same names lol
Sorry but that's not quite right! If you have an expansion tank then it does not allow water back into the system as it cools. This means there
is always air present in the coolant, a bad thing.
You can convert to a header tank by removing the sprung seal in the rad cap and then taking a pipe from the overflow to the new header tank which
must be above the highest part in the system. (You can use a take of from the stat etc. if the rad cap is not the highest point in the system. Always
take off from the highest point for obvious reasons). A return (at least one) should then be taken to a point as low in the system as possible. This
will cause any air in the system to migrate to the header and the coolant will not have air in it,. No air means you don't form pockets around
cylinders etc and is a much better way of doing things than an expansion tank! This is how it is done on modern cars.
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britishtrident
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| posted on 15/10/10 at 11:18 AM |
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quote:
Originally posted by Strontium Dog
Sorry but that's not quite right! If you have an expansion tank then it does not allow water back into the system as it cools. This means there
is always air present in the coolant, a bad thing.
You can convert to a header tank by removing the sprung seal in the rad cap and then taking a pipe from the overflow to the new header tank which
must be above the highest part in the system. (You can use a take of from the stat etc. if the rad cap is not the highest point in the system. Always
take off from the highest point for obvious reasons). A return (at least one) should then be taken to a point as low in the system as possible. This
will cause any air in the system to migrate to the header and the coolant will not have air in it,. No air means you don't form pockets around
cylinders etc and is a much better way of doing things than an expansion tank! This is how it is done on modern cars.
Sorry but that is not quite right
Old style non pressurised exapnsion tanks (as used by Honda and some other Asian manufacturers also 1970s Triumphs) do allow water to be drawn back
into the system as the radiator pressure cap always has a vacuum relief built in and this allows water in the expansion tank to be syphoned back into
the cooling circuit as the system cools.
[Edited on 15/10/10 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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blakep82
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| posted on 15/10/10 at 11:35 AM |
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quote:
Originally posted by Strontium Dog
quote:
Originally posted by blakep82
as i understand it...
header tank, hold water, has a inlet from the thermostat housing, and an outlet to the bottom hose, and has a pressure cap on the tank
expansion tank is one where off the filler neck below the pressure cap (on a radiator for example) there's an outlet which goes to a bottle
which has water in it, when the water in the system expands it goes into the bottle, and when the system cool, it sucks water back in, the the bottle
itself is not under pressure
i think... i get confused. everyone seems to call them all the same names lol
Sorry but that's not quite right! If you have an expansion tank then it does not allow water back into the system as it cools. This means there
is always air present in the coolant, a bad thing.
but then why would you want a bottle to hold the water, rather than just let it drain away onto the road and dry up?
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Canada EH!
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| posted on 15/10/10 at 02:34 PM |
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The point is you don't spread anti-freeze all over the road so your dog can lick it and die! also you are not adding coolent every week.
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coyoteboy
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| posted on 15/10/10 at 05:45 PM |
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My Toyota has an expansion tank that has a pressurised rad cap, this allows over-pressure water into the expansion tank (non-sealed) and sucks it back
again if it goes into vacuum on cooling. The water level in the bottle changes on heat-up despite it being a pressurised system.
We are arguing over terminology here I suppose, but to me a header tank is a fully open system.
[Edited on 15/10/10 by coyoteboy]
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40inches
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| posted on 15/10/10 at 05:54 PM |
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I'm with Blake and britishtrident on this, if you have a water bottle connected to the rad cap overflow,and the tube from the rad cap goes to
the bottom of the bottle, any water expelled into the bottle will be drawn back into the rad, no argument, just the facts maam, just the facts, 
With a header tank the rad doesn't have a cap, the header tank does, an expansion bottle is just what it says.
I have both; a closed rad with a header tank and an expansion bottle connected to the header tank rad cap.
[Edited on 15-10-10 by 40inches]
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Strontium Dog
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| posted on 15/10/10 at 07:46 PM |
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quote:
Originally posted by britishtrident
quote:
Originally posted by Strontium Dog
Sorry but that's not quite right! If you have an expansion tank then it does not allow water back into the system as it cools. This means there
is always air present in the coolant, a bad thing.
You can convert to a header tank by removing the sprung seal in the rad cap and then taking a pipe from the overflow to the new header tank which
must be above the highest part in the system. (You can use a take of from the stat etc. if the rad cap is not the highest point in the system. Always
take off from the highest point for obvious reasons). A return (at least one) should then be taken to a point as low in the system as possible. This
will cause any air in the system to migrate to the header and the coolant will not have air in it,. No air means you don't form pockets around
cylinders etc and is a much better way of doing things than an expansion tank! This is how it is done on modern cars.
Sorry but that is not quite right
Old style non pressurised exapnsion tanks (as used by Honda and some other Asian manufacturers also 1970s Triumphs) do allow water to be drawn back
into the system as the radiator pressure cap always has a vacuum relief built in and this allows water in the expansion tank to be syphoned back into
the cooling circuit as the system cools.
[Edited on 15/10/10 by britishtrident]
OK then, what "modern" system in any performance car is as you say?
What I said is correct and is the best way to do the job except for perhaps remote pumps via the core plug holes etc!. Expansion systems do NOT
generally include a way to suck air back in and even if they did it would be a very poor substitute for the system I have described and would not
scavenge air from the coolant as a correctly positioned and installed header tank would. Removal of the air from coolant is a major factor to consider
but often overlooked and if going for big power it is a vital consideration!
I can't really be bothered with another argument on here so for those interested try google etc!
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daniel mason
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| posted on 15/10/10 at 07:59 PM |
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so for a header tank with a pressure cap,an inlet,an outlet and an overflow from the neck under the cap. what is the best way to pipe them up?
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NS Dev
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| posted on 16/10/10 at 01:29 PM |
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lol this old chestnut always gets a good audience.
Right, lets get back to basics, and go from first principles!
Firstly, when you heat water up, it expands, and as a ball park figure without getting all anal about it, a cooling system of 10 litres, heated from
20 deg C to 100 deg C expands by 100ml
Clearly, if you fill a cooling system "to the top", then heat it up in the above manner, you will force 100ml of water out through the
pressure cap.
What "most" modern cars do is incorporate a tank of some sort into the cooling system that contains something compressible, i.e. air,
which then gets compressed to allow for the 100ml of expansion or whatever according to your cooling system capacity.
The japanese seem to stick with the older system, where you DID fill the cooling system to the top, and as Britishtrident correctly stated, the
pressure cap overflow then was piped to the BOTTOM of an OVERFLOW tank. This was topped up so that the overflow pipe was always underwater, and then
coolant pushed out by expansion is vacuumed back up as the water contracts...........
I don't like that setup, as its unnecessary if you can incorporate an air bubble on top of the water in the system somwhere.
As you will generally want the system to bleed itself of trapped air, this bubble is ideal as its a place where your various air bleeds can be routed
to, and still self bleed under pressure (assuming that the cooling system designer had enough brain cells to actually put the "bubble" as
the highest point in the system)
As you can see, no right or wrong, but as long as your tank can hold 100ml of air at a point higher than any other part of the cooling system, and has
a pressure cap fitted, and the system is free of other air traps, then it will work.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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sebastiaan
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| posted on 16/10/10 at 02:35 PM |
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quote:
Originally posted by Strontium Dog
OK then, what "modern" system in any performance car is as you say?
How about every Subaru?
Pressure cap with overflow hose to the bottom (through a hole in the top) of a non-pressurized overflow bottle. There are others, also.
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coyoteboy
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| posted on 18/10/10 at 12:11 PM |
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IMO The answer is simple. Header tank is unpressurised with a feed from the bottom, relying on rad cap to relieve pressure and allow liquid to pass.
Expansion tank is a pressurised vessel, also with feed from the bottom, pressure is regulated by using a suitably large expansion tank.
Either system is suitable, both systems can rid the cooland of trapped air providing the expansion/header tank feed is taken from the highest point of
the engine. Neither solution needs to re-introduce air unless it is incorrectly assembled.
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Strontium Dog
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| posted on 18/10/10 at 04:08 PM |
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Hi, yes you are quite right about that, I'd forgotten how they work. It's been a while since I used a expansion system.
One reason not to are that if the coolant goes much above 100deg and then cools but stays above 100deg then you can end up with less pressure than you
need to prevent boiling. This does not happen with a header system. I'm not sure exactly how to explain the mechanics of this but it is a known
thing. Not something I've come up with but a well known problem. Standard cars don't tend to go above 100deg,at least not often as stats
tend to open around 85deg, so the effect is not noticed.
Also, no engine is air tight. You will bleed gasses past the head gasket even on a good engine and glands in water pumps etc can allow air in. This
gas will be trapped until the engine reaches sufficient temp to expel them to the expansion tank, ie. over 100deg by which time you may have already
had a problem due to the cumulative gas in the system causing hot spots around cylinders. It is possibly one of the causes of cracked cylinders in
tuned 3SGTE's and why most performance engines do not use the expansion system but a header tank that scavenges air all the time.
Without getting my books out and delving to far into theory land, I hope that explains better why headers are a good thing!
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