cooalnt gauge acting strange

[s13pignose]

my car had been sitting for about a couple hrs. hang out with local car people. I drive about a 1/4 to half a mile before I merge onto the expressway and about half a mile down the road on that, my coolant gauge steadily climbs to hot, and then past the H! So I freak out, and turn the climate control all the way over to warm, but left the fans off. Pull to the shoulder of the road and pop the hood...no steam/smoke...no nothing. So I drive home with fans on, and temps go down to norm. Once home, check my oil cap for miky residue and pull one plug wire out to check down the hole. Then I read on 240sx.org to bleed coolant system, sit the car at incline and run with no rad cap till air bubbles at the filler neck dissappear. I never saw any but did it any way for about 5 mins, and rev'd lightly a couple times near the end.. all while parked on a hill at incline.

Get home and let the car sit for like 5 mins. Then check the coolant level at the filler neck, and looks fine. Don't see any coolant in the resevoir though, and can't remember if any was in there to begin with. Check oil cap and dipstick...no milky residue.

I see no coolant leaks. So is my gauge just being stupid?

T-stat, rad hoses, and rad cap have all been upgraded with in last year, and radiator flushed
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Also when I was on the expressway, with just the climate control slid to full warm I felt no heat coming through the vents, until I turn the fans on. Got heat then on all settings 1-4 or however high it goes. Most of the time though I would get some heta without fans. Should I just try filling the resevoir up and see if it disappears over time?