Overheating after a coolant flush

Symptoms

• Overheating symptoms beginning shortly after a coolant service
• Heater performance may also be poor, suggesting trapped air
• Gurgling sounds from the dashboard or engine bay
• Coolant level seeming to need repeated topping off after the flush

Likely causes

• CommonTrapped air not properly bled after the flushRefilling a cooling system isn't always straightforward, and air pockets left in the system can cause overheating until purged.
• CommonSystem not fully refilled to the correct levelAn underfilled system after a flush won't have enough coolant to properly manage heat.
• PossibleThermostat not reinstalled correctly or a new one is faultyIf the thermostat was also replaced or disturbed during the flush, an installation issue or faulty new part can cause overheating.
• PossiblePre-existing issue that happened to show up around the same timeA failing fan or water pump could coincidentally start showing symptoms shortly after a flush, unrelated to the service itself.

What to do

1. Check the coolant level immediately and top off if it's below the proper mark.
2. Follow or have a shop follow the correct bleed procedure for your specific vehicle to remove trapped air.
3. Check for gurgling sounds or poor heater performance, which point toward air still in the system.
4. Avoid continuing to drive if overheating is significant; pull over and let it cool as with any overheating situation.
5. Have the shop that performed the flush recheck their work first, since this is often covered under their service.
6. Have a mechanic check the thermostat installation and the fan and water pump if the issue isn't simply trapped air.
7. Confirm normal operation with a longer test drive once the suspected cause is addressed.

Tools and parts

• Gloves

When to call a pro

Go back to the shop that performed the flush first, since a bleed or fill issue from their service is a common and fixable cause.

Safety