Ive got a 91 civic with b16 swap and i have problems with my water temp. when its cold out and i put my heat on the temp gauge goes down about half way between normal and cold.. and if i turn the heat off it will slowly go back to normal even if im driving down the road.. It runs normal without the heat on..anyone know whats goin on?

 

Thats normal for our cars. The stock radiators are a lot larger than they need to be.
Its nothing to worry about, unless you live in a super cold area. In which case, you can slip a piece of cardboard or something similar over the front of half of the radiator. Its ghetto, but works. Honestly though, i wouldnt worry about it. Not unless your winters have near 0 temps.

 

Does your car take longer time to warm up?
If so probably your termostat is stuck open?