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.
- 1Parking the vehicle on a hill
- 2Running the engine with the heater on
- 3topping off the radiator and adding coolant to the expansion tank
- 4running the AC full blast with the radiator cap off while adding coolant
- 5tilted the car
- 6squeezed hoses
- 7considered drilling the thermostat
- 8Loosen a heater line slightly to let a small coolant dribble push air out.
- 9Keep topping off the coolant until it settles.
- 10Use a cooling system bleeding funnel kit and leave it on while the car cools down completely.
In their words
Unedited, most upvoted first, 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 ↗