Overheat-- what froze?

[Robert Deis]

Started my 86 5kTQw to run an errand yesterday, and notices a few miles
later that the temp was rising above where it normally sits.  Within 10
minutes the needle was just below the 3/4 mark on the temp gauge, and the
red coolant warning came on in the auto-check system.

I shut it down and checked things- all hoses under the hood were HOT, as
was the overflow tank, and the overflow tank was completely full- looks
like some coolant flowed out hte top as well.

Temp here yesterday was 0-5 degrees F, so I figure a valve or something
froze up-- any suggestions?

In related news, I started smelling coolant in the cabin on the same trip-
looks like I'm due for a heater core.  What else do I change while I'm in
there?

--
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  Rob Deis                  "Let the people know beforehand what the law
  MiB3347                      is and what they are to expect."
  rdeis at io.com                              -- 18th Congress, Rec. 75