I just swaped a B16 in my 90 hatch and was wondering why this happened. My tempeture gauge was right at normal a little below midline win it just drops like my car just started and was warming up. Nothing wrong with car everything fine. BUt when I stop and sit it goes back to normal again. This is driving me nutts, there is no sign of overheating it just goes up and down from below midline to cold then works it's way up again to normal temp. agh this is driving me nutts or is this normal.
thanks in advance

 

Its more than likely your thermostat in your cooling system. They get a little sticky when they get old. Cheap to replace. Part should cost like $10 max at any auto parts store. Its located right below your intake manifold on the left side of the engine. Kind behind and below the distributor.

 

Or you by any chance running your heater

 

yes I was running my heater. Why you ask will that take in effect of what happened?

 

Sounds like the thermostat to me. I would replace it because it is not that difficult.