My 2005 GMC SIERRA 1500 runs at about 180/190 degrees, and won't heat up beyond that. The thermostat and coolant temp sensor have been replaced, and I've been trying to burp the system with hit and miss results. After parking on a significant incline and squeezing the hoses with the cap off and engine running, I got a very significant amount of air out. It finally began to reach 210, closest to peak operating temp I could have, and within minutes of replacing the cap and driving it dropped back to 180/190 and won't heat up again no matter how much I drive. I also notice that the cabs heat output from the vents drops noticeably when the operating temp is low vs optimal. This is especially significant for me because I live in Minnesota.
What is happening with my truck? How can I fix this? More "burping?"
Likely still has air in the system. Start cold engine with the system filled as much as you can with the pressure coolant cap off the plastic bottle. Idle until the engine is at the operating temp and rev engine a few times to 2ooo RPM, next add coolant to the full hot mark and the air should be removed from the system.