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MG MGA - Confused about expansion tanks

Hi,
I lose some coolant from the radiator after it is filled up as it tends to be chucked out when the car gets hot. I think this is normal and not too much to worry about as the level settles down but with the filler neck being the way it is, it is difficult to tell exactly the level of coolant in the rad. I was thinking of fitting some kind of expansion tank and have seen or read about doing this in different ways. The first way is just to have a container, say something like a windscreen washer bottle that the coolant will drain into when rad gets hot and then it will be sucked back up into the rad when things cool down. I can see how the coolant gets past the radiator cap when things get hot but how is it sucked up past the cap afterwards - you would think that the cap would be closed down and it wouldn't be able to get past. The second way is to fit a proper expansion tank as fitted to later MGBs and midgets where the normal radiator cap is fitted to the expansion tank and a plain cap is fitted to the radiator. Has anyone got experience of fitting such a tank?

Many thanks

Phil
Phil

Phil

I have the MGB tank in my MGA. See here: http://freespace.virgin.net/stephen.gyles/radiator_expansion_tank.htm

Steve
Steve Gyles

Phil, the coolant is drawn back in thru a tiny one way check valve that is built into the radiator cap. I bought a small coolant recovery tank from the local parts house and made a bracket to mount it under the radiator panel behind the front valance and connected it to the rad overflow pipe. Works fine.
John H

John is correct regarding the check valve in the radiator cap, all modern radiator caps have this check valve built into them so you don't need to get a special cap. To work correctly, the secondary seal on the cap (the large disk that rides on the top flange of the filler tube) has to make a good seal. To do this, the flange at the top of the filler tube has to be smooth and undistorted (I corrected one filler tube by applying solder to the flange, then filling it smooth). The other thing necessary to make this coolant recovery system work is that the overflow hose from the filler tube to the coolant recovery tnak, has to enter the bottle from the bottom or be exended all the way to the bottom of the tank if it enters at the top. The tank also has to be vented to atmospheric pressure.

The advantage to using a coolant recovery system over an expansion tank, is that the recovery tank does not have to be pressurized as an expansion tank needs to be. This leaves you with one less pressurized hose to worry about and the tank doesn't expand and contract as the system is pressurized and doesn't develop stress cracks over time. Cheers - Dave
David DuBois

Thanks for replies - that's made it a bit clearer. John - I like the sound of your solution as I wanted the tank hidden if possible. Could you give me a bit more of an idiot's guide to exactly what your tank looks like and where you mounted it.

Cheers
Phil
Phil Parmenter

Phil
If its not overheating what are you worried about?
Mine always dumps coolant after it is filled and it settles to a level way below the filler so when I remove the cap there is no coolant to be seen! Its been like that for the last 20,000 miles and I have never had an overheating problem
David
David M

David

Taking your quite reasonable point one stage further, why do all modern cars have expansion tanks?

I suspect the answer may be along the lines that they are maintenace free for the average motorist.

I guess that you check your water level (or lack of its visibility) fairly frequently - weekly? However, with the expansion tank system, the expansion tank would normally be primed about half full. This caters for a gradual loss of water and requires inspection probably only annually.

I occasionally look in my radiator. I am always comforted by it being full to the brim. When you look in yours, there must always be a nagging doubt?

My garage floor is also dry.

Steve
Steve Gyles

Phil, my tank is about 8" long, 6" high and 2" thick. I bought it at the local parts house. I welded up a cradle for it out of 3/16" rod. A flat tab is welded to the rod and bolted to the radiator duct panel using the bolt for the clamp for the left side air duct. Than you just need to run a hose from the bottom of you new bottle to the rad overflow tube. If I need to add water to it ( maybe once a year) I just use a turkey baster.
John H

Older radiators had enough volume built in to them so that what they spit out was extra. That is why Davids car is fine. If you over fill an old system it just spits out the extra and all is fine. In essence the expansion tank is already built in to the radiator.
In new cars there is no extra radiator volume to allow the expansion. The hood heights are engineered as low as possible, requiring as low a radiator as possible. The coolant recovery tank also allows those who never open the hood of the car to have that extra level of saftey. Helps idiot proof cars.
R J Brown

I would also point out that older cars, in the late MGB era, used coolant overflow tanks and the overflow tank normally had two lines on it. One for minimum level when cold and another for maximum level when hot. This came out of the environmental movement and, like the charcoal cannister system, does a little bit to help the environment without taking away engine performance. It does, very slightly, add to the clutter within the engine compartment. I can live with that myself.

Les
Les Bengtson

Steve - I really can't speak to the subject of new cars, the newest vehicle that we have is a 89 Toyota pickup. Our two main transportation vehicles are a 53 TD and a 66 MGB. On the MGB, even though there is a fair sized header tank, one could not see the cooant level once it dropped beloe the level of the elbow of the filler tube. On the TD, while there is a large header tank, the temperature sensor is about half way down the heigth of the tank, so I never knew if the sensor was covered with coolant. Both of these situations lead me to install coolant recovery systems. The Toyota pickup also has a coolant recovery system that was factory installed.

There is really no difference in the function of a coolant recovery system and an expansion tank, both are designed to keep the header tank completely full of coolant so there is no air in the cooling system. The only difference that I can see is that one is pressurized and the other isn't.

The coolant recovery tank is also filled about half way with coolant, so it is very easy to see what the level of coolant is in it. As long as there is coolant in the tank, then one can be relatively sure that the level of coolant in the header tank if full right to the top of the overfolw tube. The difference between the expansion tank system and the coolant recovery system, is that a leak in the ovrflow tube between the filler tube and the recovery tank of a coolant recovery system, will result in the cooant not being pulled back into the header tank when the cooling system cools off, requiring a periodic check of the level under the filler cap to insure that coolant s being pulled back into the cooling system, since there would be no other way to detect a leak. On the other hand, any leak in a system with an expansion tank, would be obvious by the steam escaping under the hood (bonnet). I only check under the filler cap on a simianual basis, unless you count the glance at the level in the recovery tank when checking the oil, so there really isn't much difference in the two systems. Cheers - Dave
David DuBois

Dave,

A comment in relation to your problem that with a coolant recovery system you can't be sure that there is not a leak in the tube between the radiator cap and the coolant overflow bottle. I agree that you could have the correct level in the overflow bottle, but the level dropping in the radiator.
However, the solution to this is to check that the water in the overflow bottle is at a low position when it is cold (before a trip) and a higher position when it is hot (after a trip). This shows that it is working correctly and the radiator is full.
Even if you introduce air to the system by removing the radiator cap, or the connecting tube, the air is automatically purged by the expansion and contraction cycle.
The radiator must always be full.

Mick
Mick Anderson

Expansion tanks are a great idea and it's a shame the factory did not pick up on it and leave us some where to mount the things.
If you don't have a heater, then thats an ideal place as the bottle must be mounted slightly higher than the radiator neck.

From that above link, you don't need to make a blank cap, CPC Australia supply them for next to nothing.
http://www.cpcauto.com.au/radiator_caps.aspx
Part number 2001

Good luck.
Mark.
Mark Hester

Mark,

That is another advantage of a recovery system, it is mounted lower the the radiator cap. It also has one less hose that has to hold pressure.

Mick
Mick Anderson

Excellent link Mark for parts, but you seem to have misunderstood how an expansion tank works. The whole point of them is that you can mount them BELOW the level of the radiator filler.
Bob (robert) yes I own an MG Dwarf!

If anyone here in the States needs a non pressure cap,you can go to you nearest Case/IH tractor dealer or here-http://www.tmtractor.com/co/322fp.htm
it's from a IH Farmall Cub. Or this one with no writing on cap-http://www.tmtractor.com/co/1642fp.htm
gary starr

Any discussion on this subject is difficult because different people mean different things. I think that the term "expansion tank" should not be used.
It is clearer if the terms "remote header tank" and "coolant recovery system" be used. Then you can talk about whether they should be mounted above or below the radiator top and how to check the water level.
The "remote header tank" is the type as fitted to some cars. The radiator cap is simply a sealed cap with no valves. The overflow pipe is under pressure and the valves are in the remote tank cap. The remote header tank is actually part of the radiator.
With the "coolant recovery system" the valves are in the radiator cap, the hose from the overflow pipe is not a pressure hose and the overflow bottle is open to the atmosphere. Water is siphoned back on cooling.

Mick
Mick Anderson

Phil

we fitted a MGB tank (coolant recovery system) to the A Coupe. While the radiator was being re-cored we changed the filler neck to take a recovery type radiator cap and shortened the overflow tube. The recovery tank is located on the inner guard under the generator and the plumbing is by heavy walled rubber tube which runs along the top of the steering rack. The advantage of the tank location is that it is out of the way but the cap can still be reached for checking periodically (actually never to be honest).
Cameron
Cameron McIntosh

I said that the water was "siphoned" back from the coolant recovery system bottle to the radiator. That is of course incorrect. I was not thinking clearly. For a siphon action to work the water level in the bottle must be higher than the radiator water level.
What in fact happens is that as the water in the radiator cools it contracts in volume and this draws the water back from the overflow bottle.

Mick
Mick Anderson

This thread was discussed between 10/11/2006 and 12/11/2006

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