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MG MGA - 1500 or 1600 expansion tank
|Anyone who has considered Barney's advice (MGA Guru) about fitting an expansion tank and been confused by the US names/numbers for the replacement radiator cap (needed to assure a water/airtight seal on the radiator) may be glad to know that NTG (MG bits) carry a blanking cap originally intended for the twincam.|
The tank and bracket are of course readily available as replacement for the B and GTV8.
I went the cheap skate route; cut the gubbings off an old cap and Araldited to seal it up. Lasted me 16 years to date.
|Good to know. |
Slightly off thread, I was thinking of fitting a simple overflow tank. Because of the rad neck, I can never see if my rad has lost just a tiny amount of water due to expansion, or if there is a leak. So I thought this would help.
Is it right that if I use a radiator cap with two rubber seals, the water is sucked back in to the radiator when the coolant cools and so creates a vacuum, provided the overflow tank is vented?
I seem to remember hearing about that before, and someone saying all caps have the double seal, but mine don't seem to. Can anyone recommend one that does?
|The Austin/Morris 1300 (ADO16) used an expansion tank, but also had a standard filler neck on the radiator, fitted with a plain cap. One of those should do.|
|Dave O'Neill 2|
|Does not help you guy's but here in the states International tractors used those caps,the originals were embossed like a regular cap but the repo's are plain -|
7lb caps are here-
|Here is a nicer blanking cap-|
|Why do we need an expansion tank? Once the water has expanded, overflowed and retracted, it will not overflow any more. I have not topped up my rad for 2 years and have no exp. tank. Of course the level looks low when cold, but it is OK.|
My garage is carpeted and I don't want it to get wet. Sorted the oil by going 5-bearing. The wife is not too keen with me using her vacuum if it's going to get fouled up with anti-freeze
|"Is it right that if I use a radiator cap with two rubber seals, the water is sucked back in to the radiator when the coolant cools and so creates a vacuum, provided the overflow tank is vented?"|
Graham - I think that is what Barney is describing and what NTG's blanking unit (and the Austin 1300 and Gary's tractor) all do.
Art - I hope you will continue to be lucky.
Steve - looks good (bit worried about the carpet in the garage)
|Every time there is a discussion on overflow tanks the two systems get mixed up.|
Some talk of how many seals in the cap and others talk of blanking type caps as in the Twin Cam.
System one has an overflow tank vented to the atmosphere and a cap on the radiator with three sealing surfaces (yes, three).
One is at the top of the neck, one is at the bottom of the neck and one is a return valve in the centre of the cap.
System two has a pressurised overflow tank with a normal two seal pressure cap on the tank and a blanking cap on the radiator neck top.
The cap on the pressurised remote tank can have a return valve but it will not do anything, unless you then feed the overflow into a atmospheric tank and you then have both systems !!
|M F Anderson|
|I suppose that I should add that even with a pressurised remote tank, with excess coolant being ejected to the ground, a cap with a return valve will allow air to enter the tank when cooling. This could prevent a low pressure in the tank causing damage somewhere in the total coolant system.|
|M F Anderson|
|Standard old-style pressure caps have two sealed pressure relief valves. The primary pressure relief is at the spring loaded foot seal which will move up a bit to allow fluid to escape as it expands with heating.|
There is also a return relief valve, which is the small diameter poppet plate on center bottom of the assembly. This has a very light spring so the poppet can move down slightly to let fluid (or air) back in when fluid contracts with cooling. If there was no return relief valve the system would develop high vacuum which would collapse the hoses.
|The 5-minute time limit for editing sucks, so now you get another post. And I cannot currently upload a picture, so see here: |
The third rubber seal under the top flange is to prevent air leaking back in, so the return vacuum can draw fluid from the remote catch tank.
|So does my cap, as per picture, have a missing seal? Sorry, the picture isnt great but the small black circle at the centre is metallic. |
|That cap looks old and may need to be retired. Otherwise, the small center disc must be part of the return relief valve. Every pressure relief cap has one. Give a little tug on the center disc to see if it moves.|
Take Barney's advice and bin that cap as it is well past it's "use by date".
Yes, your cap seems to be missing a seal. Without the seal that fits against the top of the radiator neck neither of the two types of recovery system will work.
|M F Anderson|
|Thanks, I will get a new one. What's the current thinking, am I better with 4lbs or 7lbs. I was thinking 7, just to raise the boiling point, is there any down-side?|
|Fairly early in production the factory changed the spec from 4 to 7, and recommended retrofit to all earlier cars. http://mgaguru.com/mgtech/care/csm/mg289.pdf|
With 7-psi and plain water you can max out the temperature gauge before it boils. No need for anything higher. With 50/50 antifreeze mix and 7-psi the boiling point is about 255dF, up around 80-psi in the oil pressure range.
|Thanks thats interesting. 7 psi it is!|
|Roger, I don't see the element of luck. You just don't need an expansion tank, period.|
|I agree with Art.|
The standard system is fine for me.
We drive our MGA from England to Italy and back every second year, and notched up 4,500km doing the trip this year. (Last year we did the Route des Grandes Alpes, twice.)The water level settles and stays there. No overheating, no need to top up. Temperature sits around 82C, but saw 95C on the Gotthard road pass this year when heavy traffic kept speed very low. (Was first morning that the road pass was opened after the winter close.)
Standard radiator, re-cored by a PO, standard fan,18v 1860cc, original arrangement of air hoses in place. Grill slats opened a little, as usual practice.
|M D Card|
|Mike. You say your level stabilises but how do you know? Mine probably stabilises but below the neck so I never know where the level is so I keep topping up. Does yours stabilise visibly in neck?|
I have a standard system in my 1800 engined car and other than louvres in the bonnet no other mods. Car always sits at normal temperature even with hard driving in the summer here. Not had to top up the rad. all year.
I just popped into the garage to check the coolant level, as I have not added to it since we returned from Italy in May. There is about 4 or 5mm of coolant in the centre of the horizontal part of the filler elbow.
However I am sometimes tempted (despite my own logic) to add some coolant during a long trip, so the present level reflects about 1,000 km driving, some alpine and town but mostly autobahn/autoroute. (Have Ford T9 box and standard 4.3 pumpkin.)
But if I do top up, the system always only accepts the same small amount of added coolant, ejects some, and then settles at the above level. So I am confident that the level stabilises.
Thus I have no need to add coolant recovery, and like the as-original under-bonnet look.
|M D Card|
|Interesting. However long I leave it before refilling mine always seem to take the same amount of water hence suggests it isn't loosing water, but the stable level it always reaches is below the neck so I can't see it hence usually panic and add some water.|
It has been like this for a long while during which period I have replaced the engine and the radiator core.
" it always reaches below the neck so I can't see it, hence usually panic and add some water"
It is for exactly that reason I am thinking about fitting a very simple overflow (not expansion) tank.
My thinking is that when the system has cooled down, and I remove the rad cap, if all is well, it should show the system reassuringly full.
And having thought a little more about it, if you (& I) add an extra litre of coolant to the overflow tank when cool and then draw a line on the bottle to show the "normal cold fluid level", there is no longer even a need to remove the rad cap.
This thread was discussed between 23/11/2016 and 29/11/2016
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