Hey everyone! I own a 2009 Toyota Corolla LE automatic with 139850 miles, and I've had recent problems with it. So basically I changed out an old stuck closed thermostat for an OEM one and that was great. Burped the system, and now I visually see coolant flow through the rad cap hole. I changed the rad cap to replace a china made one with an OEM Toyota one, cool. However, whenever I drive a bit at highway speeds, the temp gauge slowly moves up from the middle, and eventually it goes from normal range (186F-215F) to 230F-245F very fast. Then after the drive, I open the hood and the top hose is extremely hard and feels swollen. Then when opening the cap after it cools all the way down, the radiator is missing coolant and I check the reservoir and there is a LOT of coolant in there, basically all the way filled up. I'm sure it's not exhaust gases in the cooling system, as I did a Combustion Leak Test and the color stayed original color. I really would appreciate some guidance as I am stumped. Thank you!