Rusty or dirty-looking coolant

Symptoms

• Coolant in the reservoir looks rusty brown or has visible sediment
• Possible reduced heater performance from clogging
• Coolant may look cloudy rather than clear even if not obviously rusty
• Sometimes accompanied by a slightly different smell than fresh coolant

Likely causes

• CommonOld coolant overdue for a flushCorrosion inhibitors in coolant deplete over time and mileage, allowing internal rust to begin forming.
• CommonInternal corrosion in the radiator, heater core, or engine passagesOnce corrosion starts, it can continue and contribute particles to the coolant.
• PossibleMixing incompatible coolant typesAs with coolant mixing generally, incompatible chemistries can accelerate corrosion and discoloration.
• PossibleUsing tap water instead of distilled waterMineral content in tap water can contribute to buildup and a dirtier appearance over time.

What to do

1. Check the coolant's appearance in the reservoir and, if accessible, compare it to what fresh coolant of the correct type should look like.
2. Check heater performance, since clogging from corrosion or debris can specifically affect the heater core.
3. Avoid just topping off dirty coolant repeatedly without addressing the underlying condition.
4. Have the cooling system flushed to remove old, contaminated coolant and any loose debris.
5. Ask about a chemical flush or additional flushing cycles if the coolant is very dirty or corrosion is significant.
6. Refill with fresh, correct-type coolant mixed with distilled water after the flush.
7. Have the radiator and heater core checked for any lasting damage from corrosion if the coolant was very dirty for an extended period.

Tools and parts

• Gloves

When to call a pro

See a mechanic for a proper cooling system flush, especially if coolant has been neglected for a long time, since DIY flushing can miss trapped debris that a proper flush machine catches.

Safety