temperature guage reads approx 180-190 when idling or driving in town and heater blows hot..... when out on highway driving 65-70mph temperature drops to approx 120 and heater is barely blowing warm.. just put new thermostat in along with alot of other work

 

...tell us what year, make and model and what temp was the new thermostat??

 

99 cavalier
don't know temp of new thermostat... we put it in ourselves, I have the box but nothing told me what temp it was

 

replacement should be 195, look on the old thermostat for verification of the temp.

 

Sounds like a t-stat that is stuck open

 

I agree with toyotaman. Out of box failures for thermostats are common. I recently had to go through 2 at napa, the first wouldn't open.

 

...my first thought also...a stat stuck open...or possibly misinstalled...if coolant is allowed to bypass the stat because it's not sealed in there properly (which almost always results in a leak) or the wrong stat for the application, then the engine temp will not be regulated and will run too cool at highway speeds