[V8] Coolant Sensor?

[Stafford, Kenneth A.]

So, been catching a few comments about a coolant sensor and started to wonder
about a problem my 91 has developed.  Started about an intermittent over-heat
warning in the info display immediately after WOT runs from 65-90 mph (second
gear kickdown--one of my favorite things to do!).  All temps would show
normal but the display would illuminate for about a minute after each run.
Now, it comes on about a minute after engine start and stays on all the time.
The reservoir level is full and the water temp runs consistently about 85-90
degrees (87 degree t-stat).

Another new situation (unrelated?), shortly after engine start I get a
flashing outside temp indicator on the AC panel.  I know this is a fault
indication of some sort.  I have had the AC disconnected for some time since
I replaced the compressor and just haven't bothered to purge/recharge it yet.
(Last time I checked however, it seemed like there was no heated air coming
out when I called for heat.)

Any hints?  Besides the coolant reservoir level, what other sensors trigger
the hi-temp warning?

TIA,
Ken

'91 V8Q