Thomaslv

So I guess I'll go back to the very beginning.
My girlfriend was sitting on the jumpseat of my 2000 5.3 Silverado Extended cab shortbed and she didn't realize she was gently pushing down on the gas while the car was off. When I started it, it revved to pretty damn high on the Tach, but I didn't get a good look as to what rpm, and theres no redline so i dunno if it hit redline, and I shut the car off immediately.

I drove home didn't notice anything. Went to her house. Still didn't notice anything, did some around the town driving, didn't notice. Then when I got home (maybe 15 miles later) I noticed my temp was at 235. Which is 3/4 of the temp gauge.

The next day, to replicate the temp to show my dad, we drove it maybe 1 mile, and it crept up slowly, and as soon as it hits the middle of the gauge (where it usually sits) the temp launches up to 235, and then slowly moves up and down between 210 and 235. And it does this like clockwork, always after driving about a mile.

I googled it, and every sign I was having pointed toward a broken thermostat. (My heater doesn't work either).

So we replace the thermostat, everything goes good. I drive about 15 miles, and suddenly, same thing. Temp moving between 200 and 235 up and down up and down.

When I open the hood at 235, it doesn't seem that hot. And yesterday I pulled over at 235, only waited like 10 minutes before I took the radiator overflow cap off, and the coolant didn't seem like it'd be 235.

Any ideas?