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MG MGA - Expansion Tank or Coolant Recovery Tank

OK, I have read the archives and I know have one question. What is the difference between a Expansion Tank or Coolant Recovery Tank? I have a Expansion Tank off of a MG midget that will work room wise, do I install the filler neck at the same elevation or higher then the radiator filler neck? Or does it matter?

Thanks for any Help: Cliff(SC)
Jones

Thanks Dave, I just found your e-mail on this subject. It has answered all of my questions.

Cliff(SC)

Jones

Cliff

I trust that Dave told you that it doen't matter about the relative height of the expansion tank.

Mine is installed below and works well. See here: http://www.mgaroadster.co.uk/radiator_expansion_tank.htm

Steve
Steve Gyles

I believe that a coolant expansion tank and a coolant recovery system are two different things.
The mga twin cam has a coolant expansion tank. The tank, when filled and cold, has a specified water level below the cap (see Twin Cam Workshop Manual). Water which expands in the heated radiator passes to the expansion tank, which now becomes full. When the radiator cools the water from the expansion tank runs back into the radiator.
This expansion tank must be fitted higher than the top of the radiator. Only the expansion tank has a pressure cap.
In the MGB coolant recovery system the expanding water opens the outlet valve in the radiator pressure cap and the water passes to the remote tank. The remote tank is open to the atmosphere. On cooling, a tube which goes to the bottom of the remote tank allows the water to be drawn back through the inlet valve in the radiator pressure cap. This coolant recovery tank can be fitted lower than the radiator.

Mick
Mick Anderson

Thanks Steve, if I understand I need a non pressure cap on the radiator so the hot water will pass form the rad to the exp tank through the over flow pipe without overflowing from the top of radiator and the newly installed exp-tank has the 7 lb cap to keep from over flowing.

Thanks Mick, for your input I also understand what you are saying but Steve has hit the nail on the head with what I am trying to do.

Cliff
Jones

Mick

I beg to differ. The MGB expansion tank is a pressurised tank. It has a pressure cap fitted. There is free passage of water between the radiator and the pressure tank via the overflow pipe, as shown in my photo in my previous post. A sealed (to atmosphere) cap is fitted to the radiator, but this in no way restricts the flow of water between the radiator and tank. It's been running this way in my car for several years years now and works perfectly.

Steve
Steve Gyles

Thanks Steve. My MGB comment was incorrect. I was thinking of the Triumph system with a full coolant recovery and a vented overflow tank.
However, I still have a problem following how your tank works.
Could you please advise how the hose is fitted to the expansion tank? Is the hose fitted to an opening in the top of the tank only, or is there a hose inside the tank also, going from the opening to the bottom of the tank?

Mick
Mick Anderson

Hi Mick

I have just taken a photograph and added a few notes that should explain all.

Just to reiterate, with an expansion tank system of this type it really does not matter whether it is placed above or below the radiator filler neck. The flow of pressurised water overcomes gravity. If I eventually fit a supercharger, this tank will probably be resited forward of the radiator, sitting on the air intake pan.

Steve


Steve Gyles

Steve, How do you put the notes and arrows on your pictures?
Nigel
Nigel Munford

Nigel

I do it through Powerpoint. Paste (insert) the picture on a blank page. Add any of the effects that you wish: arrows, clipart, lines, words etc. Then selct 'Save As'. In the 'Save as' dialogue box select the drop down menu in the 'Save as type' window. Then scroll down to and select 'JPEG File Interchange Format (*JPG)'. This saves your page as a JPG photo image that you can then paste to this site.

This also allows you to put about 4 pictures in one posting if you so wish, just paste all your pictures onto one Powerpoint slide.

Steve
Steve Gyles

Steve, do I use a 7 lb or a 10 lb cap on the exp. tank?

Cliff
Jones

Cliff

I am using a 7lb cap.

Steve
Steve Gyles

Thanks Steve, I will have it installed by this afternoon for our afternoon drive.

Cliff(SC)
Jones

Steve

Does the expansion tank have an overflow pipe fitted?

Regards..,JOhn
J Bray

John

Yes it does. It is sited in exactly the same position as the radiator overflow pipe. Have a look at the image I included 7 posts above.

Steve
Steve Gyles

Guys,

The expansion tank,normally, has a pressure cap fitted to it. The purpose is to allow a cross flow radiator maintain a full fluid level at all times.

As coolant warms up, it expands and excess air is expelled. We see this, in the MGA and early MGB engines as the coolant seeking a level of about 1/2" to 1" below the filler neck. Most of the time, unless there is another problem, the coolant level will remain stable at that point.

With a cross flow radiator, which does not have a pressure cap associated with it, the expansion tank will expel the excess air, allow coolant to flow back into the cooling system, and keep the coolant off the ground, something important to enviromentalists.

The "overflow" tank catches the overflow from the earlier model radiators, which had a pressure cap on the filler neck, and allows the extra air and coolant to be captured into a secure tank. As the engine cools, a vacuum forms. The "negative pressure" feature of modern pressure caps opens, and the excess coolant is drawn back into the engine's cooling system.

The only real difference is that the older expansion tank had the pressure cap fitted, and work hardened from this, developing leaks, while the "capture tank" is at normal atmospheric pressure and uses the pressure cap originally installed on the radiator. Thus, it last longer, keeps the system filled with coolant, and does not need to be replaced on a regular basis.

Les
Les Bengtson

Steve, thanks for the info re powerpoint.

I have fitted a recovery system as per Barney's site, and I used some clear pipe that I had. Should I be able to see coolant in ALL of the pipe, and if I can't, does this mean my system is not airtight?
Nigel Munford

Nigel,

Seeing air in the tube would probably not mean that it was leaking air. With any system of two liquid containers joined by a tube you can have the effect of the liquid flowing back and forth correctly but a bubble always remaining at the highest point. This is common when using clear plastic fuel filters, the filter is always only half full, but there is no leak. It has no effect on the operation, either with fuel filters nor expansion tanks.
You should consider yourself lucky that you don't have a Triumph, with the clutch hydraulic line going upwards out of the master cylinder then down to the clutch, you need a special technique to get that bubble out of the line.

Mick
Mick Anderson

Thanks Steve,
I had been looking at the earlier picture and missed the one with the detailed explanation.
Regards...JB
J Bray

Steve, just wanted to say thanks works like a top the high today was 96F never over 180F in traffic.


Cliff(SC)
Jones

Cliff

Glad it works. Where did you site the tank?

Steve
Steve Gyles

My comments on this are primarily aimed at Steve Giles but may be of some interest to others. I did fit the Moss supercharger and both I and a chap called Mike Avery in germany who also has a charger fitted both had over heating problems. He solved his problems with an expansion tank and a expensive alloy rad and a lot of new plumbing. I think ( Although its not been realy hot in England to realy test )I have solved mine by fitting a recored rad that was supplied by Bob West the Rad has a high capacity core and it appeares to have done the trick the kenlow has not been on and I am even thinking of going back to the 84' thermostat. the Fluid in the rad stays at 3/4 below the neck. Be careful I am on my 3rd re core before I talked to Bob there are a lot of bad rads out there Do we need an expansion tank if the rads working well

David
David swaine

Dave

I have never had overheating problems. When my original radiator sprung a leak I also traded it in through Bob West. The new radiator works just like the original. I fitted the expansion tank purely to stop the normal water loss and, like many other enthusiasts enjoy tinkering with the car, adding modifications etc.

I do not pretend to be an expert, but my guess is that the expansion tank and coolant recovery tank make no difference to the car's running temperature. As the engine warms up, surplus water transfers to the 'additional' tank and there it stays as 'dead' water until the engine cools down. Only the water remaining in the radiator does any work cooling the engine.

Steve
Steve Gyles

With hot summer temperatures Down-under we need extra cooling, so an expansion tank is essential. I have utilised an Austin 1800, brass (rather cute) expansion tank on my MGA (1950cc MGB motor) and it allows me to drive on 40oC days as long as the traffic is moving freely. I use a recovery cap (7 psi) on the radiator and a dummy cap on the exp. tank. It works!!
Barry
BM Gannon

Barry

I am intrigued, educate me how the extra tank provides the additional cooling. The expansion tank is a dead end repository for expanded water. It is not part of the radiator circulation system. I can understand that a minor amount of water might get drawn back into the radiator when a hot to overheating engine gets moving out of heavy traffic into free flowing air, but surely, we are only talking teaspoonfuls.

The only other way the expansion tank water can aid cooling in a small way is sometime after engine shutdown when the radiator water starts to cool and sucks the water back or pressure forces it back.

Steve
Steve Gyles

Barry

Picture of your Landcrab tank attached. It looks remarkably similar to the MGB tank. Why do you have the pressure cap on the radiator rather than the expansion tank? I have the pressure cap on the expansion tank and it also works well.

Steve


Steve Gyles

Steve, I installed in the same location as you show, it's tight but the only place that works well.

The only thing I wanted to do keep all coolant in the system, to fix my overheating problem I replaced the thermostat housing (goose neck).

Thanks to all: Cliff(SC)
Jones

Hi Guys

I take it all of you have converted your standard MGA radiator filler necks to a recovery neck? The way I understand it, the standard neck and cap will let hot, compressed water out of the radiator, through the overflow tube but won't suck it back in when it cools, no matter the relative hight of the tank and radiator, thereby acting only as a catch tank.
If a recovery neck and cap is fitted, then the hot, compressed water will move between the radiator and expansion tank based on pressure/heat, no matter the relative hights of the radiator/expansion tank.
My radiator has the recovery neck and cap conversion and the expansion tank is vented, but a knowledgable friend disagrees saying the recovery cap should be on the expansion tank. I've tried it both ways and didn't have to fill the radiator or tank either time, so I'm not sure now..... but logic says the recovery cap stays on the recovery neck, so that is where it lives now.
Regards, Dave
David Godwin

Steve
How do you moniter the fluid level. Is there a case for having a translucent expansion tank so you can see whats going on -like in modern cars?
J H Cole

We still have the problem that people cannot see the difference between an expansion tank and a coolant recovery system.
Steve has an expansion tank, with the radiator cap a permanent seal and the pressure cap on the expansion tank.
David has a coolant recovery system, with the triple seal recovery type cap on the radiator and the remote tank vented to the atmosphere.
Both are correct, but not the same thing!

Mick
Mick Anderson

John

I barely need to monitor the fluid level. About once every 6 months or so I take off the radiator cap and check the fluid is to overflow pipe level. I shine a torch in the expansion tank to check that the level is still above the bottom of the pipe. Other than full water changes following radiator/engine out processes, I do not recall ever having to top up.

Steve
Steve Gyles

Steve, If we accept the differences (see Mick Anderson above) between where the caps are located, I have a coolant recovery system. I have tried your system (recovery cap on the side tank and blank on the radiator) and on a 38oC day lost much of the fluid. I reverted to a coolant recovery system (switched caps) and fitted an electric fan and it is now working perfectly. As you don't need to top up in the UK, and most I know here do on a regular basis, my guess is the difference in summer temperatures between our two countries. I have no need to ever check the fluid level during our winter, but must check regularly during the rest of the year. I have no problems in hot conditions travelling in the country where there is a flow of air over the radiator, but in stop/start traffic it is a different story.
Thanks Mick for your comparison of the systems.
Barry
BM Gannon

Thanks to all who responded, this will be a nice one for the archives.

Cliff(SC)
Jones

This thread was discussed between 16/06/2007 and 21/06/2007

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