thermostat

[N rogge]

Hi-

Got a question:

Someone told me that if you thermostat is stuck open
it affects your gas milage.  I think mine is stuck
open because I don't get any heat in the winter, and
as soon as I get on the hwy (in the winter) my temp.
gage goes from the middle back down to cold.  If
anyone could help me with this that would be great.  I
am getting about 300 miles to a tank on mostly hwy, on
a '92 se-r, I have plugged the egr, new K&N air
filter, new triple plat. NGK, along with new NGK
wires, and a new O2 sensor.  All that money spent and
it could be the termostat?

Thanks to everyone on the list,
Nick