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MG Midget and Sprite Technical - Getting hoses to fit

This is a specific problem that I can probably cobble together a solution for. But better engineering minds may have a 'proper' solution rather than my bodges.

The expansion tank on my car has a 7mm spigot pipe, but the rad overflow is 10mm pipe both have a pythonesque ridge just back from the end. So I need a hose pipe that will fasten securely at both ends. Bear in mind this is a pressure pipe as it is the feed to the expanson tank at +15lbs.
GuyW

Is the expansion tank metal or plastic?

Trev
T Mason

Brass.
My bodge would be to try and find a short length of 7mm ID soft rubber hose, hopefully 10mm Ext Dia. If I can find that ideal size it should slide inside the end of a 10mm 1D hose. The latter needs to be reinforced to take the system pressure. Then fasten with a decent quality hose clip.
GuyW

Guy....gonna show my ignorance here but l'm way too old to care and in any case ignorance CAN be cured....my vertical flow rad has an overflow pipe running to ground ... the rad " burps" now and again and leaves an embarrassing puddle but to do so the (7 lb) cap has to vent. Is your expansion pipe on the " sealed" side of the radiator cap?. Is that even a question?.. thanks..Dave
David Cox

Guy
You could use a double ended barbed reducer 7mm one end 10mm the other----
https://www.ebay.com.au/itm/305250106078

or better still if you had a brass 10mm barb you could cut the bulge off your 7mm fitting and slide the 10 over it and sweat it on-
William Revit

A few solutions in my view. Either of Willys suggestions but you can get one with a barb one end and plain the other to sweat on or Araldite on. Also along your lines PushFit.com do a plastic 10mm X 7mm tube support but not sure if that is hard plastic or soft. If hard it may not seal.

Trev
T Mason

You are overthinking the challenge you face, Guy, or I am missing something.

15psi is not very much - in fact I have survived it for quite some time. The standard hose fits over each tank fitting bulge and is held in place by a jubilee clip. A smear of washing up liquid or softening the hose end in warm water may help with the larger fitting.

Fit as normal, run the car to temp, check for leaks and nip up the offending jubillee if there are any.

https://www.moss-europe.co.uk/en-gb/hose-radiator-to-expansion-tank-grh1005m
Karl Thompson

You make a good point, Karl....atmospheric pressure is about 14.7 psi...so any pressures above this should be designated 'psig'....as in pounds per square inch guage to indicate that the pressure is over and above atmospheric.
Oh well...l was forever moaning at my students about this...but l'm retired now so why am l still worried??...
Dave
David Cox

And David, being a bit of a stickler for such things, you will have noted in my opening post that I included. + Sign in front of the 15lbs. So ambient plus (+) 15lbs.

Agreed it is still pretty low but a leak or weep would still be an annoying problem on a cooling system, somewhat negating the use of an expansion tank in the design!
GuyW

Before sticking my wrong oar in Guy, 😄, can you confirm you have a cross flow rad?

7lbs vertical flow, 15lbs cross flow.

I'm a tad confused. Lol.

On mine, being x flow, 15lbs, the overlow is from the expansion tank, not the radiator.


anamnesis

Cross flow, Anam, but not an original MOWOG version. The pipe in question connects the rad to the input of the expansion tank, so like your crosslfow, is controlled via the 15lb pressure cap.
GuyW

Mine isn't a mowog either. It's a repro from Sussex. But it does have matching pipe sizes. That's why I wondered.

Have you tried expanding a bit of 7mm ID rubber hose, to 10mm?

I'd try that, I've done it before, but not for this particular circumstance.

It's doable with a gently heated flat blade screwdriver, rotating inside the hose. Or dipping the hose into boiling water, and immediately try pushing it onto the 10mm pipe on the radiator. Use grease (I've got a tub of Castrol red rubber grease) on the inside of the hose or outside of the 10mm pipe, to help ease the pipe over the ridge.

anamnesis

Its a Motorsport rad, Anam.

No I haven't tried expanding 7mm this time. I don't have any pipe so need to buy something. I think I will have more success using an oversized rubber pipe compressed down with a decent clip to fit the 7mm pipe on the expansion tank. I think the soft rubber will compress down more readily than the reinforcing in the wall of a 7mm pipe would tolerate being stretched, even with a heated screwdriver.
I suspect the best answer is a compromise in size, maybe using a 9mm pipe. That, or Willie's barbed adapter idea.

Of course I could go all traditional bodge and use that clear plastic pipe with the criss criss reinforcing. AppropriateLy aged to a urine yellow colour.
GuyW

Guy, did you see my comment about the PushFit tube support?

Trev
T Mason

This thread was discussed between 05/05/2025 and 07/05/2025

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