Hi-

Just picked up a '91 civic dx hatch for $150 for the wife to get back and
forth to work.. Runs good, a/c works, no rust - a pretty good deal I think.
When it was driven home approx. 15 miles and parked, it smelled pretty hot
from outside, but temp gauge was in the middle for the whole ride steady as
could be..The car had been parked for about 3 months without being run at
all during that time.
So, I put about $250 into it the next day for battery, wipers, front pads
and both sides rear brake wheel cylinders, drums and shoes, 4 quarts
max-life, a haynes manual and a new oil filter
We put it up on her uncle's lift and started working. I told him about the
hot smell driving home the night before, so we pulled the t-stat & he boiled
it and found it to be working. Put the t-stat back on and now the temp gauge
goes crazy. Goes up and down rapidly, seemingly with no rhyme or reason.
it'll show hot (all the way up) when driving at a steady rate, then go back
down to the middle less than a mile later, then go to all cold and suddenly
shoot back up to the top. This happens while driving at a steady pace,
accelerating, sitting still, basically all the time.
Did we foirget to plug something back in when we took out the t-stat? He
looked at the manual to make sure to put the t-stat back in correctly. Is
there a sensor we could've broken? Nothing looks abvioulsy amiss to my eyes.
Any ideas?

Thanks.