If your car is overheating and then the heat stops working, there are a few possible causes to investigate. Overheating can put a lot of stress on the engine and cooling system components, potentially leading to failures that affect the heat. Getting the overheating issue properly diagnosed and repaired is key to getting the heating system working again.
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What causes car overheating?
There are several common causes of engine overheating in cars:
- Low coolant – A low coolant level leaves less fluid to absorb and dissipate heat in the cooling system. Coolant levels should be checked regularly and topped up as needed.
- Faulty radiator cap – The radiator cap maintains pressure in the cooling system. A bad cap can’t maintain the proper pressure, leading to coolant boiling over.
- Broken/slippage fan clutch – The fan clutch allows the fan to disengage at high speeds when airflow provides cooling. If it’s broken, the fan may not spin fast enough.
- Failed water pump – The water pump circulates coolant through the engine. A failed pump will reduce coolant flow, leading to overheating.
- Thermostat stuck closed – The thermostat regulates coolant flow to the radiator. If stuck closed, coolant can’t reach the radiator to dissipate heat.
- Damaged head gasket – A blown head gasket can allow coolant to leak into the cylinders. This reduces the cooling system’s effectiveness.
- Clogged radiator – Debris like leaves, bugs, and dirt can block airflow through the radiator, reducing its ability to dissipate heat.
If the engine overheats, the excessive temperatures put a lot of stress on components. Prolonged overheating can lead tocylinder head warping, head gasket failure, and damage to other engine parts.
How overheating can damage the heating system
In most cars, engine coolant is also used to provide heat inside the cabin. Hot coolant from the engine circulates through a small radiator in the heating system called the heater core. A blower fan pushes air across the fins of the heater core to provide heat. This means failures in the main cooling system can affect the heating system. Here are some ways overheating may lead to heat issues:
- Head gasket failure – This allows coolant to leak out of the cooling system, reducing the amount available to the heater core.
- Damaged water pump – Poor coolant circulation reduces the amount of hot coolant reaching the heater core.
- Thermostat failure – A stuck open thermostat can reduce coolant temperatures, providing less heat to the heater core.
- Heater core leak – The high temps and pressures from overheating can cause leaks or cracks in the heater core.
- Heater control valve issues – Excessive heat may damage cables, hoses, and valves that control heater core fluid flow.
In severe overheating situations, coolant temperatures and system pressures can exceed the capacity of various components. This is why prolonged or repeated overheating should be addressed immediately to avoid cascading failures.
Diagnosing the overheating problem
Since overheating can damage many engine and cooling system parts, it’s important to diagnose the root cause. Here are some tips for diagnosing overheating issues:
- Check coolant level first – Low fluid is an easy thing to spot. Top up if needed.
- Look for leaks – Inspect hoses, radiator, water pump, head gaskets etc. for any sign of leaks.
- Test the radiator cap – Use a pressure tester to ensure the cap maintains the rated pressure.
- Check fan operation – Start the engine and ensure the fan turns on when temperatures rise.
- Inspect water pump – Check for leaks or noises from a failing bearing.
- Test the thermostat – Remove and inspect operation by heating in a pot of water on the stove.
- Pressure test system – Use a pressure tester to check for leaks in the cooling system.
- Check engine oil – Signs of coolant in the oil can indicate a head gasket leak.
Once the root cause is found, the appropriate repairs can be made. This usually involves replacing any identified faulty components. Be sure to thoroughly flush the cooling system after major repairs to remove any contaminants or accumulated debris.
Getting the heat working again
After completing overheating repairs, there are some additional steps needed to get the heater functioning again:
- Bleed air from the cooling system – Air bubbles from a system draining can impede coolant circulation and heater performance.
- Flush the heater core – Use a backflush tool to force water through the core and remove accumulated sediment.
- Check coolant flow control – Make sure cable, vacuum, and electric controls for the heater are functioning properly.
- Check blower motor operation – Test the blower fan at all speeds to ensure proper air flow.
- Replace heater core if damaged – Overheating issues may require a new heater core.
- Verify coolant temperature sensor – This provides input to the temperature blend doors.
Addressing any issues found and verifying normal operation of heating system components should have heat restored to normal. Be sure to monitor coolant levels and engine operating temperature closely over the next while to identify any new issues promptly.
| Overheating Cause | Symptoms | Diagnosis |
|---|---|---|
| Low coolant level | – Coolant warning light comes on – Visibly low coolant in reservoir |
– Visually inspect level and top up as needed |
| Faulty radiator cap | – Coolant leaks from reservoir/radiator – Coolant boiling over |
– Test cap pressure holding ability |
| Damaged water pump | – Coolant leaks from pump seal – Noisy bearing |
– Look for leaks or noises – Test pump operation |
| Stuck thermostat | – Takes long time to warm up – Doesn’t get up to operating temp |
– Remove and heat test in water – Replace if stuck closed |
Preventing overheating issues
Proper maintenance and operation of your vehicle can help prevent overheating issues from occurring:
- Check coolant regularly – Top up with manufacturer approved fluid when low.
- Change coolant per service schedule – Flushing helps remove scale and debris buildup.
- Ensure proper coolant mix – The correct 50/50 mix of coolant and distilled water provides best performance.
- Replace worn components – Inspect belts, hoses, water pump, and thermostat; replace if worn or leaking.
- Don’t overload vehicle – Excess cargo weight adds strain and can contribute to overheating.
- Clear radiator debris – Clean off bugs, leaves, and dirt from radiator fins regularly.
- Address external leaks – Oil, transmission or power steering leaks should be repaired to avoid contamination.
- Give engine time to warm up – Don’t rev high rpms until the engine is warmed up to operating temperature.
- Make shorter stop-and-go trips – This allows the engine to fully warm up and avoids cooling down during long highway drives.
Watching your temperature and pressure gauges can provide an early warning of potential overheating. Reduce speed or load if you see a sustained rise in operating temperature. Pull over and let the engine idle if it continues rising. Finding a safe place to stop at the first sign of overheating can prevent severe engine damage and related failures like heater issues.
Conclusion
An overheating engine can put severe stress on the cooling system and lead to failures affecting heat output. Common causes include low coolant, faulty radiator caps, bad water pumps, and stuck thermostats. Diagnosing the root cause of overheating through pressure testing, inspections, and checking engine oil is key. Repairing issues promptly helps prevent damage. Getting heat restored requires bleeding the system, flushing the heater core, and checking operation of heat control components. With the proper maintenance and operating practices, overheating and related heating issues can be avoided.