How often to do a full radiator/coolant flush

Symptoms

• No record of a full coolant flush, only occasional top-offs
• Coolant looks rusty, muddy, or has particles despite periodic top-offs
• Car is starting to run slightly warmer than it used to

Likely causes

• CommonInterval simply overdueFlushes are done less often than oil changes and easy to lose track of.
• CommonOnly topped off, never fully flushedRepeated top-offs dilute but don't remove old, degraded coolant and buildup.
• PossibleInternal corrosion or scale buildupOld coolant loses its corrosion inhibitors over time, allowing scale and rust to build up inside the system.

What to do

1. Check your manual for the recommended coolant type and flush interval, since intervals vary by coolant formulation (some long-life coolants go 100,000+ miles).
2. Look at the coolant color and clarity in the reservoir; rusty, muddy, or cloudy coolant suggests a flush is overdue regardless of mileage.
3. Have a full flush done, which drains the old coolant, cleans the system, and refills with fresh coolant at the correct concentration.
4. Ask the shop to check the radiator cap and thermostat while the system is open, since these are easy to inspect at the same time.
5. Bleed any air from the system per the correct procedure after refilling, since trapped air can cause overheating or a poorly functioning heater.
6. Recheck coolant level and color after a week of driving to confirm everything looks correct.

Tools and parts

When to call a pro

If the engine has been running hot or overheating, have a mechanic check for underlying causes rather than assuming a flush alone will fix it.

Safety