what is this hole for? 21 stud eng.

[fftoddster]

This hole apparently is connected to the cooling system passage. It is back of the block drivers side just outside of the pan rail. (screwdriver pointing to it)

There was nothing but a bunch of muck in it. Cleaned it out and figured out that it goes into cooling passage.

Does something go there or a plug? What size thread is it supposed to be?

[Lawson Cox]

Is it threaded? Looks strange to me.

[fftoddster]

looks like it may be threaded. I didn't want to run the wrong size tap down it and mess up threads

[Terry,OH]

3/4" welsh plug replace all four

[Keystone 34 3w]

Most of the blocks I have here have a simple old copper penny to plug the hole.

[mercman from oz]

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In the first picture, you can see that these Freeze Plugs or Welsh Plugs are covered by the Gasket and hidden from view. In the second picture, you can see these 4 Holes clearly.
Whenever you removed the Sump, make sure that you remove these Plugs and clean out the holes thoroughly. Push wire or similar up to loosen all scale etc. I collected half a jar of rubbish when I cleaned the block out through these holes.
Before cleaning these holes, my 34 was running hot. Now it runs cool. These Plugs also have the habit of leaking and letting water enter the Sump. When I noticed water in my sump oil, this was the first area that I looked at and sure enough, one of these plugs was leaking water into my sump.

[fftoddster]

No, not the welch plugs. That is part of the reason I had the engine apart is to replace those, one was leaking.

There is a small hole further back, outside of the pan sealing area. I cleaned out the hole and ran a 1/4 20 tap through it to clean up the existing threads. It goes into cooling passage.

It is the second hole in my picture past the welch plug. (not the oil pan bolt hole next to the welch plug or the very back oil pan bolt hole but the hole between the two but outside of the oil pan flange.

Thinking I just get a bolt with silicone and maybe a copper washer and plug it?

[JM 35 Sedan]

Originally Posted by fftoddster

This hole apparently is connected to the cooling system passage. It is back of the block drivers side just outside of the pan rail. (screwdriver pointing to it)

There was nothing but a bunch of muck in it. Cleaned it out and figured out that it goes into cooling passage.

Does something go there or a plug? What size thread is it supposed to be?

My eyes are not as good as they use to be, but I have looked at that picture from every angle, and downloaded it in my tablet so I could enlarge it, and I can see a hole in the pan rail where TerryO is saying the 3/4" welsh plug should go, but what looks like it could be a screwdriver, appears to be pointing to a different hole, that would not have a welsh plug.
Exactly where is that screwdriver you mention, that's pointing to a hole? Maybe if the picture you posted was a bit clearer, or beter focased, I could see what you are talking about.

[fftoddster]

Sorry I don't have a better pic

[mercman from oz]

Here is a larger picture of the Hole in question?

[fftoddster]

Yes I the small 1/4" 20 thread hole inside the red circle.

[Mart]

Don't know what it was for or who put it there, but a 1/4-20 bolt with some sealant and a copper washer should put your mind at rest.

Mart.

[Walt Dupont--Me.]

I've seen a lot of those early blocks SO full of rust they will eat a hole through the block. Chances are that block has pretty thing walls and had a hole in it and someone tapped it and put a plug in it. Walt