I had an overheating problem with my 95 civic, and took it to the shop. It turned out to be the thermostat, and they replaced it, but not it takes like 20 minutes of driving before the temperature needle barely raises up, and the heater is blowing barely warm air. What could be causing that?

 

thermostat.did they replace it with a used one?or coolant temp sensor(about $25).....other stuff idk

 

Maybe they forgot to put a new thermostat back in. The purpose of the thermostat isn't to keep your car from overheating, it's there to hold the water in the motor until it heats up to operating temperature. If your temp gauge is working properly, the only thing that can cause this is a bad/wrong thermostat. I bet your gauge and sensors are fine because your heater is blowing luke-warm air... So take it back to the idiots that did the job and (nicely) ask them to fix it.

 

I would go with stuck open thermostat.

 

is it bad to drive like that? the summer is coming, so maybe i shold just leave it the way it is until it gets cold again? and how will that affect AC performance?

 

If your engine doesn't warm up fully, your ECU won't go into closed loop (so you'll get bad gas mileage). A few degrees is okay, but if your engine doesn't get up to operating temperatures, even things like its geometry can go out... because things like tolerances for thermal expansion of metals and viscosity requirements for oil clearances won't be correct.

Just change that $6 thermostat. 2 bolts hold it in.