Coolant overheating 2019 Tahoe

[Cbiblis]

Coolant temp is getting hot and running in the 225 to 240 range depending on driving conditions. The faster I go (70 or faster) temp goes up. I slow down and not put stress on the engine, sensor goes back down to 10-20 degrees with in a mintue or two. I have never seen the temp fluctuate that quickly. I have replaced the themastate and coolant sensor 4 months ago. I just replaced the coolant sensor but still didn't fix the issue. Normally when the Coolant sensor has gone bad, it show low temps and the radio doesn't work but never seen the temps go high. Anyone else had this isssue?

 

[B-train]

Can you check the actual temp with a hand held IR gun? Check the upper hose or metal that isn't shiny for a more accurate reading.

How many miles? Has the coolant ever been changed? Has stop leak ever been added? A bypassing thermostat will increase the temperature over time and with high load because it doesn't slow down the flow enough to reject heat. Hence the slowing down and temps dropping. Might have a couple issues here.

 

[Rygrego]

Sounds like a bad thermostat. Just did mine about 4 months ago. Same issues.

 

[Cbiblis]

Can you check the actual temp with a hand held IR gun? Check the upper hose or metal that isn't shiny for a more accurate reading.

How many miles? Has the coolant ever been changed? Has stop leak ever been added? A bypassing thermostat will increase the temperature over time and with high load because it doesn't slow down the flow enough to reject heat. Hence the slowing down and temps dropping. Might have a couple issues here.

Coolant has never been changed. Has 127,000 miles and changed the thermastat about a year and half ago and then changed a couple of months ago. I haven't bypassed the thermostat. I was going to changed the coolant this weekend and put the old thermostat in because I don't believe the thermostat was bad but the first coolant sensor was. I put a second sensor in a few months ago and it solved this issue with low coolant temps. Thank you for your input.