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MG Midget and Sprite Technical - Brass Radiator Plug

It's almost Springtime in Western New York - so during my pre-season prep routine I noticed that there is no rubber over flow hose on my radiator expansion tank. Is this just a convenience item - possibly just add about 18 inches of rubber hose, point it down to the ground and just be done with it?

However, the bigger problem is that I now cannot remove the brass radiator plug on the upper left side of the radiator. I used to lay a large screw driver across the slot and it would turn - last night, No Go. I don't think it has ever been replaced...

My questions is: should I apply heat from my propane torch? I can't seem to find a socket or wrench that will fit. Should I just dress the sides of the plug with a flat file to make the closest socket size fit? If so, any thought on the actual size? Will the top of the radiator tank deform if I put some torque on it?

I really don't want to go with the BFH solution if I can avoid it..

Thanks for any input.

Mike P.
Buffalo, NY

Mike Pelone

Mike that screw is the same size as your plug spanner

And it is better by far to have the brass ones than the fibre based plastic ones fitted to some British Leyland cars in the seventies. When they sieze, which is often enough if the cooling system is run without antifreeze/inhibitor in it, the head can break off leaving the screw thread section stuck in the hole.

Not fun...

IIRC the spark plug socket fits
Doug Plumb

As above - spark plug socket.

I would NOT advise heating it with a propane torch. You may melt the solder holding the tank on, with obvious results!
Dave O'Neill2

Hey Guys - Thanks for the quick reply - must be the Time Zones kicking in...

Sounds good - I will apply the flat file technique until the spark plug socket just fits.

Also, should I just extend the expansion tank over flow tube down to the ground? The pressure cap fits very tightly on the expansion tank - but not sure why it requires a pressure cap - does the over flow hose would just allow any pressure to escape...would this be just an "open system" in any case??

O.K. - back to the morning coffee. Spring rains today so no midget on the road this weekend..

Mike P.
Mike Pelone

Hi Mike,

Regarding your second question, are you asking why the Midget cooling system is pressurized, or are you asking why the pressure cap is on the expansion tank rather than on the radiator itself?

if the latter, then it is because the cross flow radiator doesn't really have a "top tank" to provide the air space for the expanding coolant to occupy, meaning that when it cools, the top of the matrix will be exposed unless there is an external tank for that expansion and contraction to occur in

This arrangement is not all that common in the auto world, but is used whenever a crossflow radiator does not provide that expansion space above the matrix.

Regarding the overflow hose, you are correct, its only purpose is to keep the engine room tidy (make any overflow drips occur down near the bottom of the car, out of sight).

hope this helps,
Norm Kerr

I've always used a 21mm socket which is probably the same size as a plug socket(?)

your plug look a bit knarled but it might fit

I'd use a good penetrating/releasing fluid and leave it to soak as long as possible (overnight) then a slight move to tighten befire undoing, if it didn't work more good penetrating/releasing fluid and leave it to soak as long as possible

there should be a rubber O-ring on the plug and it pays not to squash that too much, as I found out

antifreeze/coolant conditions in other ways so it's worth changing at the required intervals which is before it's looses it antifreeze abilities
Nigel Atkins

Go gently with it! The metal that forms the radiator jacket that the blanking plug screws into is fairly thin and if you exert too much force on the plug it can twist, deform and even tear. If it is really stuck then I would add a little heat with a torch, but not too much as Dave says or the soldered joints will melt.

another good point from Guy, if you feel even slight flexing then best to stop, spray, leave longer, try again later

reminds me of the time I had to get the immersion heater element out of my neighbour's old hot water copper cylinder, balancing effort against metal bending and disaster, instead of the nice box I had a cheap ring spanner version trying to decide if the flexing was spanner or cylinder
Nigel Atkins


O.K. - Upon closer examination, I can see where the rubber seal from the radiator cap contacts the inner lip inside the neck of the expansion tank "below" the height of the over flow outlet hose connection.

Whereas, that other hose which connects between the radiator and the expansion tank is "below" that level. Now I can see how the pressure cap creates the pressure when sealed - and over flows only when something is amiss..

In closing, any idea as to the correct pressure rating of the proper cap - I have to assume that sometime during the past 40 years, somebody must have replaced it.

My '72 RWA runs at acceptable temps on the road so I would think that the cooling system is in proper order - but a fresh coolant change will be in the works for later this month.

Mike P.
Bflo - NY

Mike Pelone

Cap should be 15 lbs for cross flow radiators.

An alternative to the rubber seal is to use a 'fibre' [Klingersil or similar] washer under the filler plug.
Doug Plumb

you'd do well to fit an overflow pipe to save hot water blowing in the engine, as you say a bit of hose hanging lower than the chassis

if you're going to change the coolant do yourself a big favour and clean the engine block waterways as this is very often missed and you'll be amazed at the crude that builds up, a bit of bent wire helps to scrape out the build up and what flushes to the drain hole in the block

(see Driver's Handbook for full details of drain and refill or many other threads on here)

below is full list of what I do:

before starting check for working and conditon -
. coolant hoses, if any need replacing consider using silicone hoses (and rond-edged clips) as current rubber products are rubbish
. fan belt (more convenient to change now that at roadside)
filler pressure cap (check seal)
. thermostat
. heater tap (leaks, fully turns on and off)
. fan (clean and secure)
. water pump

a) clean the whole coolant system with something like Bars Flush Cooling System Cleaner

b) drain the whole system - engine block, heater matrix and radiator

c) get the radiator and heater matrix out of the car to give them a good shake at the same time as flushing and back flushing
∑ flush clean water through each of the three until water runs out thoroughly clean
∑ reverse flush each of the three until water runs out thoroughly clean
∑ final flush through each of the three until water runs out thoroughly clean

d) gently brush clean both sides of the radiator fins

e) gently brush clean the heater matrix and renew the seals and foam around the heater matrix and heater box case

f) premix coolant and water mixture (if required and note tap water isnít always the best water to use, distilled would be better) to the correct ratio and to the correct quantity for a full refill (you may not use it all if you didnít remove the radiator and heater matrix)

f) refill with the coolant mixture

g) follow the refill instructions from the Driverís Handbook to avoid getting air locks or Ďhotspotsí that could cause overheating of the engine
Nigel Atkins

This is interesting. I do not have a rubber o-ring, fibre washer or any other type of washer on my filler plug and it seals up perfectly. Not believing what I was reading here, I checked in my MOSS catalogue and, sure enough, a rubber o-ring is listed. Is an o-ring really necessary I ask myself?
Chris H (1970 Midget 1275)

I've never had an O-ring on any crossflow radiatored Spridgets.
Dave O'Neill2

obviously if two people have successfully not used them then they not strictly necessary

but possibly if one is fitted then the brass plug wouldn't be tighten down so much making it easier to remove years later - if only for the fact with the gap the o-ring provides it means a good releasing/penetrating fluid can get in and run easier

as far as I can remember (and that's not saying too much) my last Spridget had an o-ring and my present Midget came with one

personally I think the o-ring helps also because you don't have to (perhaps) over tighten the plug making remove easy - yes you may have to renew the o-ring before it perishes but that's not an arduous task

not that the brass plug on mine has had a chance to seize on as itís had to be removed far too many times and too often
Nigel Atkins

This thread was discussed between 21/04/2012 and 22/04/2012

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