Also, it goes away after you drive it a while in conditions that warm the
engine more, like idling or driving around town.

However--get this--I just talked to a vendor, who asked me, "Is it in the
right way?"  His idea was that if you put the thermostat in backwards, or
upside down, then the coolant pressure from the pump would force it open,
causing this problem of overcooling.

Do they fit in backwards in the 1.9?

How else could you explain the phenomenon that the t-stat opens in hot
water, closes normally, but sticks open in the car? Also, at idle, the water
pump pressure would be less, perhaps allowing the thermostat to close.

OK, guys, I need to read "Thermostats for Dummies."