Re:  "low 50's ambient........it could very well be that dropping to  very low temp on the gauge is normal under those conditions."  and "The coolant temp should not drop to a very low reading during a long descent in the summer."

We just returned from a 1,000 mile round trip to Eagle, AK during which I let our `87 Westy Syncro coast on some long downhill grades(6-9%) and our temp guage dropped to slightly above the cold mark.  Ambient was probably around 50F.  Our 2.1L is a bit different than the 1.9L but does exhibit the same behavior.

Mark in AK