Thanks to everyone for the great suggestions so far. Instead of watching
things from the inside of the Tiger, I started it from dead cold this
morning and observed things to see the sequence of events. Before
starting it, I made sure all the hoses were tight, including on the
heater core, and checked for any evidence of obvious leaks, (none) etc.
I also made sure the cooling system was full (I topped it off last night
as it did need some water. It has been using some, and it has not been
sucking the water back into the cooling system recently from my extra
overflow tank when the car cools down).
I turned the heater on (valve open), left the heater core cover/latch
reciever off so I could see and feel the heater core and started the
car. It warmed up slowly, and leveled off at about 170 degrees for a
couple of minutes. Heater air temp. was luke warm, not hot, though.
Then, after two or three minutes, the water temp. shot up, going to 230+
on the guage. Air temp from the heater was still only luke warm. There
was also a very noticable amount of white smoke coming from primarily
the left (driver's side) exhaust pipe. I normally get a bit of smoke
from both pipes in the morning when cold, but it goes away after the car
warms up. This is different, in that this morning there was a lot more
smoke coming from the left pipe. Also, the coolant overflowed a bit at
the same time the temp went way up. Then, pretty suddenly, water temp.
started dropping and went all the way down to 170-180 (with the
auxillary fan on), normal for the car in this weather. At the same time
the water temp. went down to 170, the white smoke from the left pipe
also went away. I idled the car for about 20 minutes, water temp. stayed
between 170-180, and no more smoke. Also, as soon as the water temp
dropped to 170, the heater started blowing hot air, and the heater core
went from feeling just warm, to hot, as you'd expect with hot water
running through it.
We'll see if the water from the overflow tank is drawn back into the
system as it cools now, but I doubt it from recent experience.
Any further comments or ideas out there?