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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?"

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  • I just tried again. Added more coolant, got the engine to finally warm up to operating temp. It held for 5 minutes and dropped back down again.
    – Ben Hopson
    Jan 9, 2022 at 22:30
  • Welcome to Motor Vehicle Maintenance & Repair! Bleeding the system should not be an issue as these trucks "self bleed" due to the style of cooling system they are. There is the bottle which is actually where the radiator cap is at. This has a separate small hose attached which feed back into it and is above the coolant level. This bleeds air out of the system. All you should have to do is keep the system at the full level and that part of it should be golden.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 9, 2022 at 22:36
  • During/after engine warmup,does the cooling fan run? For better temperature monitoring, use a reader displaying coolant temps. Was this cooling system drained and flushed with clear water, allowing a full warmup while testing heater output before draining and refilling with antifreeze? Was sealer or old coolant muddy? If crud built up, sometimes the heater hoses clog and need to be disconnected and flushed manually to force out blockage before heating is restored. Be sure all small hoses are free of debris blockage to minimize wasting expensive antifreeze.
    – F Dryer
    Jan 10, 2022 at 2:54

2 Answers 2

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The only reason an engine does not get to operating temperature is a missing, defective or misinstalled thermostat.

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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.

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