Here's why:
* Overheating: The overheating likely caused damage to the thermostat, which regulates coolant flow. A stuck-closed thermostat prevents coolant circulation, leading to overheating. The force of the overheating might have even cracked the thermostat housing.
* Temperature Gauge & Heater: The temperature gauge and the heater both rely on coolant flow to function. If the coolant isn't circulating properly due to a faulty thermostat or a damaged housing causing a leak, neither will work.
Other possibilities, though less likely given the circumstances:
* Coolant level: Check your coolant level. Air in the system can also interfere with temperature readings and heater function.
* Wiring: While less probable, the overheating might have damaged a wire related to the temperature gauge or heater circuit. Check for any obvious melting or damage to the wiring harness in the engine bay.
* Temperature sensor: The temperature sensor, which feeds information to the gauge, might have been damaged by the heat. This is less likely than the thermostat issues though.
* Gauge itself: It's possible the gauge itself failed due to the electrical spike during the overheating. This is the least likely scenario.
Troubleshooting steps:
1. Check coolant level: Add coolant if needed to the proper level (check your owner's manual).
2. Inspect the thermostat housing: Carefully examine the housing for cracks or leaks.
3. Replace the thermostat: This is the most likely solution. It's a relatively inexpensive and easy repair, even for a novice mechanic. Make sure to get the correct thermostat for your specific engine.
4. Bleed the cooling system: After replacing the thermostat, you need to bleed the air out of the cooling system to ensure proper coolant circulation. Again, your owner's manual will have instructions.
5. Check for wiring issues: Visually inspect the wiring harnesses near the thermostat housing and temperature sensor for any damage.
If you're not comfortable working on your car yourself, take it to a mechanic. The repair is likely relatively inexpensive, but diagnosing the root cause is important to prevent further damage.
