Quirky thermostats

[Lines Peter]

Are you sure your gauge is correct?  The reason I ask is that I recently
battled this same problem on an '86 4kq.  It turned out that the thermostat
was fine.  In fact, the engine was running at normal temperature, but I was
getting a "low" reading on the dash gauge.  The reason was that the temp
sender was exposed to cold air blowing through the grill.  Once I rigged up
a small shroud, the temp gauge came back to normal.  Also, I'm getting
better mileage now because the CIS temp sender is also behind the shroud.

Peter Lines