Clogged or Restricted Radiator
A clogged radiator cannot release enough heat, causing slow temperature rise, overheating under load, or poor cooling at highway speeds.
Can I Drive?
fix-soon
Most Likely Causes
- 1
Internal mineral scale or rust
Old coolant or mixed coolant can leave deposits inside radiator tubes.
- 2
External debris blocking fins
Bugs, leaves, dirt, or bent fins reduce airflow.
- 3
Stop-leak debris
Sealers can clog narrow radiator passages.
- 4
Poor coolant maintenance
Degraded coolant loses corrosion protection and can build sludge.
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How to Diagnose It
- 1
Check temperature difference across radiator
Cold spots can indicate restricted flow.
Tool: Infrared thermometer
- 2
Inspect external fins
Look for debris, mud, bent fins, or blocked airflow.
Tool: Flashlight
- 3
Rule out thermostat and fan first
A good radiator still overheats if coolant flow or airflow is missing.
Tool: Scan tool, observation
How to Fix It
Clean external radiator fins
Remove debris carefully without flattening fins.
Flush system if contamination is mild
Flush only when appropriate and use correct coolant afterward.
Replace restricted radiator
Severe internal restriction usually requires radiator replacement.
Parts & Tools
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Related Issues
Bad Cooling Fan Relay
A bad cooling fan relay can stop the radiator fan from turning on when the engine gets hot. This can cause overheating at idle, overheating in traffic, weak AC performance at low speeds, or a cooling fan that only works sometimes. The relay should be tested before replacing the fan motor because a fan motor can look dead when the relay is not sending power.
Blown Cooling Fan Fuse
Blown Cooling Fan Fuse means the fuse protecting the radiator fan circuit has opened, usually because the fan circuit drew too much current or shorted The repair should start with power, ground, fuse, connector, and load testing instead of guessing at modules or replacing parts at random.
Cooling Fan Control Module Fault
Cooling Fan Control Module Fault means the electronic module controlling fan speed or fan command is not switching the fan correctly It can cause overheating, fan warnings, AC performance problems, or intermittent fan operation depending on the vehicle.
Other Cooling Issues
Browse more diagnostic guides in this category.
AC Compressor
Your ac compressor is the heart of your air conditioning system, pressurizing refrigerant to cool cabin air. A failing compressor will leave you blowing hot air and typically requires replacement rather than repair.
AC Compressor Car
An ac compressor car component is the heart of your air conditioning system, pumping refrigerant to cool cabin air. When it fails, your AC stops working entirely, leaving you in uncomfortable heat.
AC Compressor Cost
AC compressor cost typically ranges from $500 to $1,500 at a repair shop, including parts and labor, with DIY replacements costing $100–$400 in parts alone. A failing compressor reduces cooling performance and can damage other AC components if left unaddressed.
AC Compressor Oil
AC compressor oil is a specialized lubricant that reduces friction inside your compressor and keeps it running efficiently. Low or contaminated compressor oil can damage your AC system and lead to expensive repairs.
AC Compressor Price
AC compressor price varies widely based on your vehicle make and model, with costs typically ranging from $200 to $1,500 or more for parts alone. Professional installation adds labor charges, making total replacement costs significantly higher—often $500–$2,500 at a shop.
AC Compressor Pulley
The ac compressor pulley is a spinning component that engages and disengages the compressor from the serpentine belt to control when your air conditioning runs. When it fails, your AC won't work properly and you'll hear grinding or squealing noises from the engine bay.
Mistakes to Avoid
- Do not pour stop-leak into a system that already has radiator restriction.
- Do not pressure-wash fins aggressively enough to bend them flat.
- Do not replace the radiator before checking fan operation and thermostat flow.