TR2/3/3A TR3A Block Drain Puzzler?

[karls59tr]

I drained the radiator coolant for winter as it sometimes reaches -35C here in the dead of winter. When I went to drain the block I discovered that the drain petcock was missing. I understand that some TR3's had a plug instead of the drain tap but neither was there. The odd thing is that I've been driving it all summer and haven't noticed any coolant loss and I do check it every now and again.It never overheated either. There was some evidence of leakage on the block under the tap opening. Is it possible that the drain hole was blocked enough with crud that it only leaked a minor amount? Was low pressure in the system preventing a major leak!!! I'll have to stick a piece of wire in there and clean out the opening and see if coolant pours out.

 

[Andrew Mace]

I'd say it's definitely possible, based on a few drain tap/plug holes I've cleaned out over the years! Be sure you've got something to plug the hole with once it's clear, though; I think it's a pretty typical thread and that you can get a petcock from a hardware store (such as you might find on a more modern radiator or even on, say, the bottom of the air tank of a compressor).

 

[MGTF1250Dave]

Aloha Karl,

I agree with Andrew, it is quite common for the petcock to become plugged with rust, minerals and other crud circulating in the cooling system. The lower rear portion of the block doesn't have alot of water flow, so solids in the coolant tend to settle in that portion of the block I often have to poke a stout wire through the petcock to get coolant to flow. A 4 PSI radiator wouldn't put a lot force on any blockage.

I believe the petcock has 1/2" x 20 TPI UNF threads. The hole in the block is approximately 1/2 inch deep.

Periodically I remove the petcock and flush the block with a "water jet" I made using a piece of brake line and a small fixed hose nozzle. It lossen up and gets the crud moving around so it can be washed out of the block. Here is a photo of it.

 

[karls59tr]

Thanks for the info guys. Karl