Overheating

Ok, I will be replacing the coolant temp sensor and the thermostat tomorrow and be back to say if that fixed it or not. I know when it comes to a blown head gasket there are signs like a coolant leak, milky oil, bubbling in the reservoir or white smoke either from the exhaust or under the hood and none of those things have presented.

So I swapped out the coolant temp sensor first so I wouldn’t lose too much coolant if that was the only issue and when I took the old one out it spewed out at first like there was an air pocket almost similar to when you put mentos in coke and then went to a steady stream after putting that in I took the coolant reservoir cap off and started the engine and let it run for a minute or two trying to get any air out of the system went for a drive around the neighborhood 2 times at about 15-20 mph and it held steady at the 210 I then pulled out onto a main road where it’s 35 and it slightly started to overheat and when I pulled back in my driveway I popped the hood and left it running to look and I noticed bubbles in the reservoir which I hadn’t seen before any thoughts?