I have an '05 Nissan Altima that was getting hot, cooling down - repeat, while driving. I noticed it this morning on the expressway (going ~75). My needle went from its normal center position to almost touching the H within a few seconds. Around 5 sec later it cooled off and went back to the center. 30 seconds later, it repeats. Today, on the expressway it did the same but the needle went all the way to H. I pulled over, popped my hood and there was antifreeze steaming everywhere around the radiator.

I didn't see any holes/leaks/bursts. I let it cool off, added some antifreeze and started back rolling. Within 20 seconds it shot back up to the H. I pulled over and repeated the process. Did this 3 times and decided to park it off the exit so I cruised about 25-30mph for a mile and a half and she did just fine.

Thermostat? Water Pump? Anything else it may be? I checked the oil for water and we're good there. Instead of tossing parts at 'er, I figured I'd ask! Thanks in advance!