Coolant Leak

For all cars made before 1945
Hardaker
Posts: 5
Joined: Sun Oct 09, 2016 1:44 am
Name: Ian Hardaker

Coolant Leak

Postby Hardaker » Sat Nov 05, 2016 4:46 pm

I have a cylinder head gasket coolant leak on my 1936 SIlver Eagle... and I realise that it should not have any coolant going between the head and black through the gasket, so it must be one of the aluminium pluds leaking.
I replaced them when I rebuilt the engine a few years ago, but I noticed then that they were quite a loose fit, and used a sealant on them... Clearly it is not working! Has anyone done anything to improve this, I know that the threads are a parallel BSP thread , has anyone tried tapping them out for the next size up tapered thread NPT pipe plug for instance, or any other cures for this?

johnlayzell
Posts: 151
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: Coolant Leak

Postby johnlayzell » Sun Nov 06, 2016 9:26 pm

Have you tried plumber's Teflon tape?
1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

Hardaker
Posts: 5
Joined: Sun Oct 09, 2016 1:44 am
Name: Ian Hardaker

Re: Coolant Leak

Postby Hardaker » Sun Nov 06, 2016 11:11 pm

Hi John, I think I had Teflon tape on some of the plugs, but not very tight, so I used a sealant as well... Can't remember what!
I want a permanent solution next time I do it. Also is there a reason that the plugs are aluminium? Doesn't that give an electrochemical reaction with the iron head and block?

DaveT
Posts: 96
Joined: Tue May 22, 2012 12:53 pm
Name: David Turnage
Location: Colchester, UK

Re: Coolant Leak

Postby DaveT » Mon Nov 07, 2016 9:12 am

Hi,

I used PTFE plumbers tape to increase the resistance and make the threads appear tight, but you could use a screwcutting lathe to manufacture some oversize plugs to suit your engine block. It would be difficult to manufacture these without the block to trial fit the new plugs - however this is tricky because the registration of the machined thread will be lost each time it is removed from the lathe for test fitting!

The plugs are aluminium to act as a sacrificial anode - they are designed to gradually erode from the inside to reduce corrosion of the iron block and the (copper / brass) radiator. I would hope that they last at least 10 years but this assumes that you are using anti corrosion inhibitors (within the anti freeze) and replacing all the coolant every 2 to 3 years. I know there are environmental concerns about the "old style" antifreeze but newer OAT type anti freezes are not suited to older engines and the components used within their cooling systems. Also check the battery earth connection to the engine - this may contribute to more rapid erosion of the anode, but is likely to be evident when starting is problematic. This is easily checked with a parallel jump lead from battery terminal to engine block - does the engine turn overfaster? are there more volts available to the ignition?

Hope this helps
Dave
Dave T
Colchester, UK
sp25 DHC
Jensen 541

Hardaker
Posts: 5
Joined: Sun Oct 09, 2016 1:44 am
Name: Ian Hardaker

Re: Coolant Leak

Postby Hardaker » Sat Nov 12, 2016 3:04 am

Thanks Dave, I think I will try and make up some custom tapered thread plugs. NPT pipe threads are tapered, but the wrong thread. I believe that the Alvis ones are BSPF, but I can't remember the sizes. I think they are 3/8" BSPF and 1/2" BSPF. Can anyone confirm? I figured that if I make some tapered ones like NPT, they will tighten up and seal when they reach the thicker end of the thread. I have access to a good machine shop and CNC machines which should make this easy! Incidentally, why do they need to be sacrificial anodes?

RichardWallach
Posts: 348
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Re: Coolant Leak

Postby RichardWallach » Sun Nov 13, 2016 5:19 am

Ian,

I believe that they were sacrificial due to the dis-similar metals and the electrolysis that would take place. We mitigate those factors today with the coolant chemicals that inhibit corrosion. These cocktails were not available really until the later 60's. I remember the days when soluble oil was added to mitigate corrosion.


Richard,

Melbourne

Hardaker
Posts: 5
Joined: Sun Oct 09, 2016 1:44 am
Name: Ian Hardaker

Re: Coolant Leak

Postby Hardaker » Sun Nov 13, 2016 2:48 pm

But why not make them out of cast iron, then they would be the same metal, and no corrosion. I know you are on the right lines Richard, but why do they have to be sacrificial? What are they saving?

RichardWallach
Posts: 348
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Re: Coolant Leak

Postby RichardWallach » Mon Nov 14, 2016 7:06 am

Ian,

Radiator tanks were often made of brass and with the early Alvis motors the block to head water transfer ports were made of aluminium. To add to this the chassis was running at a positive potential. Rolls Royce went negative earth to help mitigate corrosion. Hope this helps.

Richard
Melbourne


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