Mysterious 3VZ-E coolant leak

Greetings yet again. I looked in my 3VZ-E engine repair manual (1992 Toyota 2WD 5-speed manual pickup) to see if I can find any reason why
coolant is leaking out of a hole on the engine block, between the engine block and the fire wall, near the center of the engine.
http://desertphile.org/coolant-leak1.jpg
http://desertphile.org/coolant-leak2.jpg
I have circled the location in the images above. I crammed my finger down there and it sort of feels like the hole that the coolant is coming out of is threaded--- but I cannot tell, since so far I have not been able to put a bolt in the hole (the engine is too hot).
The leak is after the thermostatic valve--- the coolant does not leak out when the engine is cool.
The hole feels like it has a mounting bracket in front that supports another hose (a 1/4 tube).
Is there anyone out there that can tell me why this is leaking? Is there a plug?
--
Nemo me impune lacessit.
"The test of all knowledge is experiment. Experiment is the sole judge of
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 27 Apr 2013 14:40:01 -0700, Desertphile

P.S. The hole is below the temperature sensors, below the inverted "U" shaped Engine Coolant Temp Switch hose/tube. It is just below the metalic tube for the Engine Coolant Temp Switch, and it looks like a bolt used to go in to that hole and support, with a bracket, the tube for the Engine Coolant Temp Switch.
--
Nemo me impune lacessit.
"The test of all knowledge is experiment. Experiment is the sole judge of
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 27 Apr 2013 14:40:01 -0700, Desertphile

Could it be a block coolant drain plug?
--
In the past ten years, nine of them were the hottest on record (the
Super El Nino year of 1998 makes number 10). 16 of the past 17 years
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 5/2/2013 1:01 PM, Desertphile wrote:

There is a 3VZE on Ebay at the moment with some very good photos, maybe it will help you see where its at. item 390592923788 JC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.