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MG Midget and Sprite Technical - Coolant Leak

I'm absolutely new to British cars- I'm working on a 75 midget. It's been sitting for about 7 years got it to actually start up tonight. (with new plugs, wires, points, condenser etc.) I put coolant in it and wanted to make sure it was getting through the block so I blew some air in radiator hose on the right side. There is a hole on the left side of the block towards the back. Coolant poured out of this hole when the air was blown through. Is this hole supposed to be plugged? What's it's purpose?
Thanks for your help!
Mighty Midget 75

Hey Mighty,

welcome abourd, 7 years ... now thats a project, hang around you you will have a great time

Im certianly not an expert on the 1500, But I do have a good moss catologe

When you say "There is a hole on the left side of the block towards the back" Is that from the point of view of facing the engine OR sitting in the drivers seat.

Plus When you say hole in the block... do you mean a machined hole (intentionally manufactured) or is this a blow out hole where something bad happened... just for clarity

looking at the moss catologe there is a drain hole on the left side of the engine towards the back as your facing the engine from the front... its ref number 24 & 25 on the blow up diagram (bolt and cooper washer)

Moss part Number...


seriously just a bolt and cooper/fiber washer from the hardware store will work

Hope that helps... dont hasitate to ask if you need more help

Oh and we want to see pic's of your ride, we always love to see pics of everyones ride and if she will be modified or kept stock

Here is a copy of the Blow up from moss

Luck to ya



That said above... On the cly. head there appears to be a (coolant plug) Its not saying Im just guessing! that is in the same genral vicinity.

Its ref number 31 on the blow up, it almost looks like a pipe thread fitting,,, for like a oil pan drain

anyway good luck, others will be by soon to make any corrections i may have mis-led you on. (certianl wouldnt be the 1st time) thank god for good friends that know more then I.


You were right. The opening is so corroded it took me a while to confirm there were threads in there.
This is exactly what it is-
Item 24 328-445 PLUG, drain
Item 25 324-671 WASHER for plug
Does anyone know what size bolt this takes? Going to hardware store in the morning.

Thanks for the help!
Mighty Midget 75

If no one can provide the answer, what i do is break out my tap and die set and run various taps in the hole until I get the proper tread, size, and standard...these threads are whats known as whitworth its a british standard... but dont worry Ive found whitworth threads to be ither metric or SAE. Just depends on the size of the hole and the courseness of the thread
besides you wont find (easily) whitworth hardware here in the usa or whithworth wrenches, and if you do, well you really dont want to unless you have a gold bush growing in your back yard.


Another thing you can do is hunt around the engine and the bay area and find similar looking size hardware, remove it and try it in the hole that needs filling, Once you find one that fits properly simply take the piece with you to the store and match it up, many times the store will have a little test ledge with various sizes of nuts and screws you can compare it to and it will have the size written under the test pieces

eventually I want to make a board with all the various sizes, courses, and standards for both nuts and bolts so I can mount it to my shop wall,and always know what size and course I need before going to the store... well at least be able to hire a kid for a saterday to sort out all my jars and cans of hardware into a proper storage sizes... NOW that would make life easy.


Prop, I am impressed! ;-)
Guy Weller

The parts referenced as 24 and 25 in the first diagram are the drain plug and associated fibre washer for the coolant jacket in the block. This is situated towards the rear of the block on the RIGHT HAND SIDE looking forward (just below and to the rear of the exhaust manifold).

On the 1500s it was a simple plug, on the earlier 1296, 1147 and 948cc engines it was a proper drain tap.

If memory serves me right (off the top of my head) the thread is 3/8 NPT.

Despite what it says in that Moss Online Catalogue link, the part is freely available from them. If you can't get it from an MG dealer in the USA try a Triumph specialist.

Drain Plug: Part No. 129077

Fibre Washer: Part No. GHF346

Drain Tap (alternative to plug): Part No. 602915A

In the second diagram, the part referenced as 31 is a plug in the waterway in the cylinder head. This is a hangover from the fact that the motor in it's smaller cc guise(s) had a different arrangement for the water runs to the heater (and no heated inlet manifold). The heater tap was originally screwed into the cylinder head here (a la the 2000cc GT6 and 2500cc TR5/6 motors). This plug is exactly the same as the sump plug (1/2 inch BSP IIRC).
Deborah Evans

Hey guy,

Dont think to highly of me yet!... that little episode last night was ALL PAIN killers, certianly not my normal way of thinking...LOL


Hey deb,

If that is just a common (national Pipe thread) plug couldt "Mighty" just go to a local hardware store to source it...theres nothing special about it is there?

most likely just a brass fitting in the plumbing section

Deb 3/8BSP is the same size as the temp gauge thread in A series heads, so might this actually be a 1/8BSP instead on Mighty M's engine

A rough guide is that 1/8BSP is about 3/8" dia (0.383") and 3/8BSP is again, about 5/8" (0.656") diameters measured at the top of the thread.

OK I did say roughly didnt I :-)
bill sdgpm

This thread was discussed on 05/05/2010

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