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MG Midget and Sprite Technical - 1275 crossflow radiator, overflow pipe.

On my midget crossflow radiator, the overflow pipe comes out of the side of the rad, at the same level that the top hose connector. (Well in the mid level actually). See RED marker in picture.

On the crossflow rads being sold now, the overflow pipe comes out of the rad, BELOW the top hose connector. See WHITE elipse. So presumabley, the rad holds less fluid as it will overflow to the expansion bottle.

Comments?

Lawrence Slater

AFAIK the pipe has always been below the top hose connection, however, the pipe goes through the tank and turns upwards.

It is visible through the larger opening.

I did post a photo of it a couple of years back.

Your rad must be non-standard.
Dave O'Neill 2

I've found the photo...

Dave O'Neill 2

The Midget rad is off the side. The crossflow rad I just bought from Sussex to convert the Sprite, is below the top hose connection.

I'll have a look through the opening Dave. Maybe that's how it is too.

If it's not, and that's how they are being made, is this likely to effect cooling much?
Lawrence Slater

I'm with Dave on this. My first rad (which I assume was on the car when it was built) had the overflow below the top hose and the two rads I've had since have been the same.
graeme jackson

No idea how old it is, but it doesn't look new. This is the overflow on my '73 Midget.



Lawrence Slater

Graeme. I don't suppose you looked inside to see if the rads you bought had a riser pipe, as shown in Daves photo? Where did you buy your rads?

This is the one I just bought from Sussex. The pipe just goes straight in. No rise on the inside at all. Hence the level of the water will be way below the top hose connection, as it will drain to the expansion bottle. --

The only way to prevent that I assume would be to mount the bottle higher than the top of the rad, which isn't possible.

Has anyone else bought a crosslow rad recently? Is the overflow pipe like mine? straight in and stops without rising inside?



Lawrence Slater

It sounds like another case of parts being made to the wrong spec.

It looks vaguely correct, but is anything but.
Dave O'Neill 2

Just spoke with mgbhive. They say there is only one supplier. If so, this is all you can get now. I got them to check their stock, and the pipe just goes straight in and doesn't rise either.

Maybe this isn't a problem at all. But I'd rather not fit it and then have to argue that there's something wrong with it when it overheats.

Wasn't there a thread recently about someone with a 1275 crossflow setup overheating? If so, maybe this is why.
Lawrence Slater

The height of the "overflow" is irrelevant as you fill the rad with the expansion tank part of the sealed system, and the cap tight on. As you fill the rad and the level rises above the overflow pipe water doesn't immediately simply drain into the expansion tank because it is sealed and the back pressure prevents water from flowing that way. ( apart from maybe a little as the air space in the expansion tank will theoretically compress a little).

Try filling the rad with the expansion tank cap off and it will of course simply overfill and overflow through the expansion tank!

Within the rad (and the rest of the cooling system) any air should work its way to the highest point, usually with a bit of squeezing and manipulation of the larger hoses. This air is initially best evacuated via the top heater hose as being the highest point on the system.

Thereafter, the expansion tank will take any excess water and/ or air as the system heats up. This would be slightly more efficient at dispelling air with the extra upturned section of overflow pipe. But the critical part is when it cools down again as it will ONLY suck in water as it cools - assuming the level in the expansion tank is correct. After two or three cycles of heating and cooling it will normally have then automatically purged itself of any air with or without that upturned pipe section.
Guy W

Is that an 'official' explanation Guy?

I'm having trouble getting my head around the level not changing, even though the 'expansion'(overflow) pipe is set lower in the rad.
Lawrence Slater

I wonder why BMC/BL engineers went to the trouble of making it like that if it was unnecessary?
Dave O'Neill 2

Lawrence - Guy has hit the nail on the head. You can fill the rad to the level of the filler on the right as long as the pressure cap is on the expansion bottle.

For the level to drop it can only go to the expansion bottle. It can only do that if the air in the bottle can escape, which it can't if the cap is on properly.

Try inverting a glass, putting it rim-first in a bowl of water then pushing it under and you'll see what he means.
RS Hughes

Dave, l did day that the system would be more efficient at discharging surplus air with that upturned pipe. But even then it still isn't at the highest point in the system, especially if you have a heater fitted. The expansion pipe has no real effect on how full you can get the rad header so long as you are doing so with the expansion tank cap fitted.

Lawrence, as you fill it water will start off down that pipe but very soon will stop because in effect someone has their finger over the lower end of the pipe (ie the pressure in the expansion tank)
Guy W

Guy,

Actually that upturned pipe isn't very good at discharging air as it's in the incoming water stream. When I had a head gasket leak and the system was getting pressurised and forcing coolant out of the system I moved the expansion tank take-off to the top of the other header tank, by the filler, where air collects and problem solved, coolant stayed in the system and the air vented.
David Billington

Lawrence makes an intersting observation.

The copper/brass rad on my car (before I owned it) had the expansion tank pipe outlet near the top on the side - this would be in about 1980 on a 1969 car. It was re-cored at a later date - maybe 1986 and later still replaced with an alumninium alloy copy. I've recently noticed the aluminium rads on ebay for the Sprite/Midget have that outlet pipe in a different place to mine and assumedly because they are based on a different version of the copper/brass rad. My car being a 69 was early in the production run of the vertical flow rad cars (and expanstion tank) and assumedly during production the factory moved the outlet pipe on the radiator for reasons only known to themselves.
Daniel Stapleton

OK thanks Rod, Guy. Pressure. Yup got my head around it now. It was elsewhere this morning. lol.

So why originally was the pipe on the side near the top? Daniel confirms it. Was it moved because of the problem David Billington described?

Sounds like I have the original radiator still in my '73 Midget, -- or at least an early replacement.

Either way. Thanks for the clarification. I can go ahead and fit the thing to my Sprite now.
Lawrence Slater

All of the 1275s that I've had have had the pipe below the top hose connection, including my first Midget, which was nine years old and only one owner. The rad was believed to be original.

I'm sure I have seen rads with the pipe in the side of the tank, but I'm not sure if that was an early or a late mod.
Dave O'Neill 2

Could it simply be cost?

Is it easier/cheaper to put in a straight pipe, rather than a pipe with a 90 deg bend in it?
Lawrence Slater

This thread was discussed between 17/06/2015 and 19/06/2015

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