New radiator expansion tank.

[cass3958]

Five or six years ago I fitted an expansion tank to my S Type that someone nick named “The bladder bag”. It consisted of an aftermarket screen washer bag placed under the left wing with a pipe coming from the over flow on the radiator to the bag. It worked really well and I had minimal fluid loss for several years. This year I noticed the water level dropping again in the radiator and when I checked the “Bladder Bag” I saw the plastic had hardened and the bag had split. Rather than buying a new one I decided to change the set up I had to a brass expansion tank. The one I went for came from an MGB and is normally painted black. I bought a second hand one off EBay and stripped the paint off and polished it up. I have a gap on the inside left wing where the RB340 rectifier used to sit but having gone to an alternator this has been removed.
The tank cost me £30 from EBay plus a day or so polishing it up and I bought the stainless steel bracket direct from the MG owners club for £11. The expansion tank is connected by some silicon hose and the drain goes through the hole in the inner wing not that this should be required. A bit more brass to polish and it might not be original but it can be removed at anytime.

The purpose of an expansion tank is simple and all new cars are fitted with one. The water in the engine and radiator expands when hot and on a normal Jaguar S type when it expands you get a small amount of water dripping from the over flow pipe on the radiator cap often this is steam. With an expansion tank the water expands and runs to the expansion tank which is kept half full of water. The tank fills up but no water is lost. When the engine and water starts to cool the water in the expansion tank is drawn back into the radiator keeping your fluid levels full all the time.

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Expansion tank 4.JPG (1.66 MiB) Viewed 1739 times

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Expansion tank 2.JPG (1.31 MiB) Viewed 1739 times

[RollyTG]

That looks great. Goes nicely with your polished brass radiator top.

[cass3958]

Why thank you good Sir.

[John Quilter]

I use a similar set up but my expansion tank is located in the LH fender well as the voltage regulator is where yours is located. To make this system work properly you do need a flat radiator cap for the radiator. The pressure cap is on the expansion tank.

[JCS]

This thread is quite interesting from a terminology view as well as the actual arrangement. No one has commented but two different systems are described: -

1. A simple overflow system where the radiator is pressurised but the overflow pipe and overflow container are at ambient pressure. Used initially by Cass with his plastic bag and in fact myself for the last 55 years on various cars.

2. A system that has the complete overflow system fully pressurised including the overflow pipe and tank, effectively this is a radiator header tank extension. This system was original used by manufacturers to enable packaging of lower front ends whilst maintaining header tank height and accessibility. In the case of Rover, they used the pressurised overflow, unusually without excessive height on the Rover 2000 TC to make up for loss of coolant by inserting the oil cooler in the bottom radiator tank.

Both systems will allow coolant overflow and reversal coolant flows, but the fully pressure system No 2 can be potentially dangerous, depending on the header tank location and the hose and clipping arrangement. This system also does not allow the radiator cap to be depressurised unless the system is cool.

I have system No 1 with the metal header tank under the left wing (fender) but with that expansion tank overflow pipe well below suspension height, avoiding any coolant or steam egressing over the disk brake.

Although I utilise the MG overflow tank it is fitted with a flat cap whilst the radiator has a 7lbs normal pressure cap. This maintains the cooling system completely full and under bonnet access is completely standard and safe.

Has anyone thought about these systems?

Norman

[John Quilter]

I think what you are achieving with the system you described is just going to prevent any coolant from spilling out onto the ground (or your garage floor). I do not see how any coolant forced out of the radiator and into the overflow tank is going to be returned to the radiator when it fully cools down and develops a slight vacuum. The system I am using with the flat cap on the radiator and the pressure cap on the overflow tank is modeled after what BMC used on the 1100/1300 range, one of which I own.

[Glyn Ruck]

With modern long life OAT & HOAT coolants (up to 15years with some) most modern cars have, surge/expansion/header pressurised tanks which take the place of large radiator tanks & are virtually totally captive systems other than minor managed air venting to atmosphere with coolant expansion & vice versa with cooling, and will have a max fill to point/line on the tank that leaves plenty of coolant expansion space above that without liquid loss to atmosphere. Many of these systems have air purge devices from high spots in the engine water jacket etc. These tanks should ideally be mounted above the highest point in the water jacket with low crossflow radiators. Modern cars of course warn you of low coolant level.

Our old girls were designed to dump hot excess expanded coolant in the top tank of the radiator to the road with bottom only sealed radiator caps ~ no longer permitted in most countries. The reason your owners manual tells you to check coolant level DAILY.

The answer with regular radiators like ours is generally the fitting of an overflow tank with a vented lid at atmospheric pressure.

Both systems have a specified pressure caps. Overflow systems use top & bottom sealed Radiator caps with the overflow between the seals connected to the bottom of the overflow tank which needs to be kept partially filled with coolant. As the engine heats up it will expel expanded coolant into the overflow tank. There is a valve in the radiator cap. As the engine cools it will draw a vacuum at this valve in the cap, pop it open & draw coolant back into the radiator top tank to keep it full.

Both systems work fine & keep you fully topped up. The big difference being that modern systems lose very little coolant to evapouration & seldom need checking more than once a year & might need minor top up. Top up can either be done with premix but generally deionised water will do as the active ingredients in the coolant do not evapourate. If you are concerned about concentration a refractometer is your friend.


Good point by Norman. We all need one or the other. I can't make my mind up which way to go so I'm simply using a zip tied in place simple overflow tank with pipe running to the bottom.

[Glyn Ruck]

John ~ see my post. With a dual seal cap (which most are) coolant returns to the radiator by vacuum on cooling perfectly with an overflow system. They were used for years in the automotive industry. That's what Norman & I are doing at present. Works a treat & always has. Top tank of radiator always full. Vacuum & atmospheric pressure.

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Radiator cap cold..JPG (40.1 KiB) Viewed 1706 times

[NigelW]

I'm using the same tank as John (fitted in the same location as Rob's) on my car and have experimented with using both types of systems by swapping types of caps between rad and tank e.g. pressurising the overflow tank or using a plain cap and the same with the rad if you see what I mean. So far both systems work equally well so still not made my mind up which is best, at present using the plain cap on the overflow tank.

Thanks for mentioning details of yor tank Rob, I have a new metal tank the same as yours in my shed that I picked up for a song a while back but didn't know what is was from and couldn't find a suitable strap, now I know it's from an MGB I'll have to get one and change over from the plastic tank fitted.

[cass3958]

If you contact the MG owners club on +44 (0) 1954 230928 you can either buy the whole expansion tank and bracket for around £65 or as I already had an old tank I bought of Ebay for £15 then polished up I just needed the bracket which I asked for and it cost around £11.
It does not show the bracket on the diagram but they sell one and it is stainless steel. They even sell the fixing nuts. The MG tank is brass but then painted gloss black if bought new.
https://www.mgocspares.co.uk/acatalog/M ... B__29.html