Normal EGT - Very Low CHT

I was flying yesterday and noted on my GEM that on cyl #1, the EGT was
normal, but the CHT was very low. Most of the time the CHT was off the
scale low, so there was essentially no reading, but occasionally it would
come up enough to be at the bottom or one bar from the bottom of scale.

I can't think of a scenario which would cause normal EGT, but CHT 150 deg
lower than normal. The engine runs normally. So I'm suspecting a bad CHT
sensor although it if failed outright the GEM manual says it would just be
missing all the time. Any other ideas? (This is on an IO-520 in a Bonanza,
BTW.)

- Mark