How to get trapped air out of a car cooling system
Trapped air pockets prevent coolant from circulating properly, causing the engine to overheat despite topping off the radiator. This air often leaves behind an empty expansion tank and a distinct sloshing sound under the dashboard as coolant struggles to fill heater cores and passages.
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.
- 1Parking the vehicle on a hillDid this help you?
- 2Running the engine with the heater onDid this help you?
- 3topping off the radiator and adding coolant to the expansion tankDid this help you?
- 4running the AC full blast with the radiator cap off while adding coolantDid this help you?
- 5tilted the carDid this help you?
- 6squeezed hosesDid this help you?
- 7considered drilling the thermostatDid this help you?
- 8Loosen a heater line slightly to let a small coolant dribble push air out.Did this help you?
- 9Keep topping off the coolant until it settles.Did this help you?
- 10Use a cooling system bleeding funnel kit and leave it on while the car cools down completely.Did this help you?
- 11Driving around to bump the system and knock air pockets looseDid this help you?
- 12Putting the cap on to build pressure and letting remaining air work its way outDid this help you?
- 13Filling the reservoir, putting the cap on, and letting the cooling vacuum draw in coolantDid 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.
“persistent air/microbubbles in coolant system.”source ↗
“Air and microbubbles in coolant continue to come from the rear coolant neck bleeder. Tilted car, squeezed hoses, etc etc. no matter what, I still can’t fully bleed.”source ↗
“Replaced my water pump, filled coolant and tried to burp the system on a hill with the heat on but the engine keeps getting hotter than usual and nothing is coming out of the radiator cap”source ↗
“Omg I think I made a mistake the pin is supposed to be at 12”source ↗
“Got coolant drain and filled a week ago, now sloshing sound under dashboard and low coolant”source ↗
“Expansion tank looks empty and I removed the radiator cap, and it is not filled to the top.”source ↗
“I’ve been driving it for almost a week like this. Only noticed the sloshing last night and decided to check the coolant.”source ↗
“Ran idle with no bubble for 10mins but still get bubbles when I turned the car off?”source ↗
“air pockets shaking loose when the pump stops, happens to me every time i do a drain and fill on my old camry, just keep topping it off til it settles”source ↗
“I have the coolant bleed funnel kit and was getting less and less bubble each start and stop.”source ↗
“I’ve noticed that there are still small bubbles continuously bubbling up from the funnel, even after around **40 minutes of bleeding**.”source ↗
Where this came up
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