What size is this hole?

[zachmac]

The PO at some point added (I think its not original) what looks like a radiator drain on the head between the two temp sensors in the plug valley.



I'd prefer to just plug the hole going forward.



I took the drain to the hardware store and it seemed to be a 1/4 inch pipe thread but that plug is too small (loose in threads and would fall through if I kept threading it in). I suspect it is the same size as some of the various other plugs in that area? Anyone know what size it is and where I get one?

[spidernut]

I'm not sure of the hole size, but that was somebody's answer to bleeding the air out of the system. That's a really odd place to put the drain valve (also known as a draincock and petcock).

[zachmac]

I'm not sure of the hole size, but that was somebody's answer to bleeding the air out of the system. That's a really odd place to put the drain valve (also known as a draincock and petcock).

Agreed, that's why I just want to plug it. It's hardly like its the high point compared to either the heater hose connect or the thermostat housing.

[zachmac]

No one knows? Still stumped by this. I could put the old piece back (cleaned up) but I'd really prefer to just plug it. Not the same size as the drain plug in my radiator, I know that much. Definitely tapered threads. Calipers put it at like .54" / 13.76mm at the widest point.

[76was124]

As far as I know a .54 inch nominal diameter is 1/4 pipe thread, but you say that a 1/4" store bought plug doesn't fit? Was that at a plumbing store or somewhere else? There are different NPT types, I forget the names, but one is designed for an interference thread, and one requires Teflon tape ( picture plumbing fittings) to seal even though it's also tapered.

Did you compare the max diameters of the valve thread vs. the plug's max diameter?

One other thing may be to check what is the hole? Did you mic it, or put the non fluted ends of drill bits in the hole to guage it? Is it tapered, or straight? Never know what the previous owner did....

If the old valve thread fit tight and sealed, I would take it to a local hydraulics fitting store, or a local industrial cutting tool supply shop and they can probably guage it for you and or provide an equivalently threaded plug.

[zachmac]

Yeah, figure it has to be pipe thread. BUT, pretty sure the hole in the head is a straight tap with no taper.

Maybe someone can at least ell me if their 2 ltr head has a hole there and what's filling it?