doesnt know if this helps but i kinda had the same problem the day i put my b series into my civic. Whenever i was driving the car wouldnt over heat. but the second i stopped at a light, that needle went up quick. I had figured ouyt that there was air in the hoses and it wasnt allowing for the fluids to cycle through the motor. I finally figured out how to bleed the hoses and checked for leaks. after a bit of tampering with bleeding and adding a little more liquid because i was low, everything turned out perfect. You may just want to check your fluid levels and squeeze the hoses to make sure that there is fluid and not air in them, if there is air, then your thermostat will not react properly and your motor will over heat.

Chris
AIM:GotVTEC20