Why is my car overheating after changing the thermostat?
Air trapped in the cooling system prevents coolant from circulating properly after the replacement. This trapped air stops the radiator from filling completely and causes the temperature gauge to bounce erratically or spike to dangerous levels within minutes. Because the hot coolant isn't flowing, the engine quickly overheats and the cabin vents blow cold air.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Burping the cooling system to remove trapped airDid this help you?
- 2Squeezing the upper radiator hose to push bubbles outDid this help you?
- 3Revving the engine slightly to activate the water pump and dislodge trapped airDid this help you?
- 4Checking the engine oil to ensure it isn't milky, ruling out a head gasket leak.Did this help you?
- 5Verifying that the cabin heater still blows hot air.Did this help you?
- 6Letting the truck idle for an hour to confirm it doesn't overheat.Did this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“While driving it bounces up and down between the 1/4 mark. I think that’s about 160 degrees. Is it normal for it to do that?”source ↗
“I start filling the radiator back up and I notice that it’s not really filling up all the way, i can see it at the bottom of the radiator fill but I can’t fill it all the way up to the neck.”source ↗
“With my obd scanner I notice that the temperature was at 235 F after about five minutes(maybe even less) so I decide to shut it off before it got hotter.”source ↗
“The ac fans were also not blowing hot air but I’m not really sure if they ever have because I’ve never used them before.”source ↗
“Does your temp gauge bounce back and forth when driving? It’ll go up maybe 2 lines and drop.”source ↗
“I just never seen the temp bounce up then down while driving.”source ↗