Temp gauge goes into red but everything seems normal

You may have more than one thing going on. One thing for sure, the stock gauge is almost worse than an idiot light. The gauge on my truck goes to about halfway at 180°F and stays there to over 200°. If it's boiling over, way too hot.

 

head gasket

 

Not sure this will help. I had an accord, first time in several months I flipped the switches to run the heater, suddenly I got all kinds of weird symptoms. This was years ago so I don't remember all that happened but my temp gauge was jumping back and forth normal, hot, normal, hot. I found the radiator to be way low on coolant, no leaks found. Filled it up, ran it to get it hot, allowed to fully cool off, radiator needed a little bit more coolant, then the problems went away. Until the following week when the plastic end tank failed, the little part that sticks up for the radiator cap to screw on completely broke off. Replaced the radiator and thermostat, which was stuck open. Before all this happened, I had noticed I went 3 or 4 miles on the highway and the temp was still showing cold. I had planned to investigate a possible stuck thermostat on the upcoming weekend.

Now I occasionally flip switches to get the coolant cycling through the heater core. I also like to get rid of the plastic end tank radiator on every vehicle I own.

If your getting a symptom after switching defrost on, you should look at the air conditioner clutch and belt. Check the belt, it might already be chewed. Engine running, have someone switch to defrost while you watch the clutch activate. I had a ac pump going out, with ac on, it would spin, stop, sorta spin, stop. Then the ac pulley totally seized and destroyed the belt.