Just a Tiny Leak
 

So irritating and frustrating...
The wet spot on the driveway. Smelling Anti-freeze. Having to refill the overflow tank every few months.
Had to find the problem.

https://lh3.ggpht.com/_4xQFBZJE2fI/TI...0/DSC08162.JPG
The Toyota thermostat housing 'O' ring where the parts join; upper right quadrant, there was my leak.

Then I looked down...
https://lh4.ggpht.com/_4xQFBZJE2fI/TI...2/DSC08165.JPG
Replacing the timing belt, the radiator was bumped, maybe by a wrench.
Eventually, expansion and contraction opened the hole and,
although the yellow color Amsoil Propylene Glycol Antifreeze and Engine Coolant can stop itsy-bitsy leaks, this became too large.

https://lh3.ggpht.com/_4xQFBZJE2fI/TI...2/DSC08180.JPG
Perhaps, the tiny hole in the center tube.

I suppose the moral to the story is; Do the job right and...be careful.