Why won't coolant flow into the engine and the thermostat open?
Trapped air prevents coolant from reaching the thermostat, which stops it from opening and allowing fluid to circulate. This causes the heater to stop working and prevents the system from pulling new coolant out of the reservoir, even after idling the car for an hour.
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.
- 1filling the reservoir to the topDid this help you?
- 2running the engine for a bit and pouring a little bit straight into the radiatorDid this help you?
- 3Jacking up the front end of the vehicle to help the system burpDid this help you?
- 4Squeezing the upper radiator hose to force fluid throughDid this help you?
- 5Taking the vehicle for a short test drive to see if temperatures remain normalDid 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.
“I got the hose connected again but I cant get the coolant flowing from the reservoir back into the engine.”source ↗
“The heater does not work so I know the thermostat isnt getting any coolant flowing to it. I ran it for a bit and poured a little bit straight into the radiator and still cant get any to flow or the thermostat to open”source ↗
“Im terrible at cooling systems for some reason and they still confuse me sometimes.”source ↗
“I am now replacing the coolant in it but the thermostat doesnt seem to be opening? Or maybe it is and didn't take any coolant?”source ↗
“Ive had it idling for the past hour its not over heating and no more bubbles are coming out of the radiator but I never had to fill it past the initial refill of the radiator.”source ↗
Where this came up
People with this problem also raised
- 4Why is radiator coolant still green after multiple flushes?
- 3What happens if you overfill engine coolant past max line?
- 4Do I need to flush the coolant when replacing a cracked radiator?
- 6Do I refill engine oil based on what I drained or the manual?
- 10How to fix a coolant leak and sludge in an old car
- 6How to get trapped air out of a car cooling system