Cooling system weirdness

[sciroccos at earthlink.net (Jim Ruffi)]

Hi.
The trip home was a definate test of a lot of my car's parts.  Luckily,
nothing broke.  I had replaced some hoses, the metal coolant pipe, added the
missing "bypass" hose and filled the system with red dexcool-compatible
long-life coolant.  When I originally finished the changover, the water pump
impeller-to-housing gasket leaked a little.  I was able to snug it a little
and the dripping stopped, but it bugged me.

David U. told me he had heard of a couple of other people who converted to
that type of coolant and had leaks...

About 2 hours after my return from Cincy, I went to move the car and found a
tiny puddle below the car.  I checked the car and found a very tiny amount
accumulated where the lower hose-to-waterpump connection and much more
coolant leaking out of the seam of the expansion tank.  The PO had changed
this tank at some point and it looked to be in otherwise good shape.

I had the system filled to the "high" mark when it was cold and it was a bit
above the mark when hot.  The car ran nice and cool in the 90 degree heat,
with the gauge in the lower end all the way home.

Maybe I overfilled the radiator?  Maybe the red coolant somehow creates a
higher system pressure?  Maybe a defective cap, combined with too much
coolant cause the tank fracture?  Maybe the red stuff is too "leaky" for my
old car?  good thing I made it home ok.

Any advice would be much appreciated.

Jim