'90 V8Q: Hot coolant temp!

[Chris King <cking@legend.txdirect.net>]

The last couple of days I have noticed a strange behavior from my V8.
Whenever I am idling, say at a stop light or fast food window, the coolant
temp gauge gets really high.  While waiting at McDonald's today, the needle
went past the 120 celsius mark, which is all the way to the right.  I was
only waiting for about 5 minutes.  As soon as I got back on the road, it
dropped back down to around the halfway mark, which is about 100 celsius.
No warnings or anything ever came on to tell me the car was overheating.

Also, and I don't know if this is connected in anyway or not, my oil
temperature has been getting hotter that it had been.  It had been staying a
little to the right of the second hash mark on the gauge, but recently I
have seen it get up to the 130 celsius mark.  I am running Mobil 1 15-50 oil...

Any ideas what might be causing this behavior?  Granted, it has been in the
mid-90's here the past few days, so that doesn't help, but the coolant
doesn't seem like it should heat up at idle that quickly.  Could it be a
faulty thermostat?  Or is the coolant gauge just small, meaning that maybe
all the way to the right means 1/2 to 3/4 on another car?

TIA!

---
 Chris King           ===================================================
 cking@txdirect.net    '94 Corrado SLC        (Sherry Red/Beige Leather)
 San Antonio, TX       '90 V8 Quattro           (Black/Platinum Leather)
                      ===================================================