How do I properly drain and refill coolant?

What steps do I follow for a coolant change? How do I bleed air from the cooling system after a refill?

When performing a coolant/antifreeze drain and refill, it’s essential to follow the correct steps to ensure the cooling system functions properly and avoid overheating issues. Below is a step-by-step guide for mechanics.

Before the Job

✔ Confirm the Correct Coolant Type – Use the manufacturer-recommended coolant (e.g., ethylene glycol or OAT-based).

✔ Inspect the Cooling System – Check for leaks, rust, blockages, or worn components (radiator, hoses, thermostat, water pump).

✔ Assess for Contamination – If coolant is dirty or sludgy, recommend a cooling system flush before refilling.

During the Job

🔹 Drain the Old Coolant

•Open the radiator drain plug or remove the lower hose.

•Dispose of old coolant safely, following environmental regulations.

🔹 Flush the System (if needed)

•If contamination is present, flush the cooling system to remove debris.

• Ensure the heater core and radiator are fully cleared.

🔹 Refill with the Correct Coolant Mix

•Add coolant/antifreeze in the right concentration.

•Fill to the recommended level based on manufacturer specifications.

🔹 Bleed the Cooling System

•Run the engine with the heater on full to remove air pockets.

•Check for proper circulation and thermostat function.

🔹 Check for Leaks & Pressure

•Inspect hoses, radiator connections, and the expansion tank.

•Ensure there are no overheating issues or system leaks.

After the Job

✔ Recheck Coolant Levels – Once the engine cools, top up coolant if needed.

✔ Confirm No Leaks or Airlocks – Double-check system function.

✔ Inform the Customer – Advise on the next coolant change and any issues found.