Thread: Leaking 2a

Originally Posted by Dante

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The whole is definitely in the plug, not the block and I have no idea how it got there. It is alloy, so it shouldn't have rusted away.
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Dante

If you have cast iron and aluminium alloy in electrical contact and immersed in water (which is exactly what you have here) you have an electrochemical cell or battery, which will dissolve the alloy, which is the lower metal in the electrochemical series. How rapidly this occurs depends mainly on the conductivity of the water in the system (and the temperature).

It can be prevented almost completely by the use of corrosion inhibitors present in all modern coolants - but this was not the case for the 2a -- "Use soft water wherever possible; if the local water supply is hard, rain or distilled water should be used" (Series 2a Owners Manual Part No 4482). Most owners would have used whatever water was available, especially if it was using a bit of water.

John

I would prefer to have this plug corode away rather than the block itself. It is in this case working as a sacrificial component. The plug is for the redundant heater core hole. It should be a BSP plug, which uses a Whitworh threadform. A hardware store or plumbing centre will have a plug for this. Mine is now brass, as there other threaded plugs that are aluminium to sacrifice themselves elsewhere.

Be careful when purchasing a new plug, as BSP is measured by the nominal internal pipe diameter, not he external diameter of the thread. Thus 1/2" BSP measures more than 1/2" accross the thread.

The 1" British Standard Conduit Thread (16 TPI) plugs are the two to the left of your broken plug, and above the cup welsch plugs. These are also aluminium and prone to corroding through.
Aaron.