* Air in the Cooling System: The most likely culprit. When air gets trapped in the cooling system, it can create gurgling noises as the coolant flows and the air bubbles move around. Accelerating increases the coolant pump's pressure, making the air bubbles more noticeable. The heater core being on further exacerbates this as the coolant flows through it at a higher rate.
* Low Coolant Level: If your coolant level is low, air can more easily enter the system, leading to gurgling.
* Coolant Leak: A small leak, perhaps a crack in a hose or a failing water pump, can allow air to be sucked into the system, again causing gurgling.
* Faulty Radiator Cap: A faulty radiator cap might not maintain proper pressure in the system, allowing air to enter.
* Water Pump Issues (Less Likely): While less likely to directly cause gurgling, a failing water pump *could* contribute indirectly by reducing coolant flow and allowing air to accumulate.
What to do:
1. Check your coolant level: Open the hood (carefully, let the engine cool completely first!), locate the coolant reservoir, and check the level. If it's low, add coolant (the correct type for your Civic – consult your owner's manual). Never open the radiator cap when the engine is hot.
2. Inspect hoses and connections: Look for any signs of leaks, cracks, or loose connections in the hoses and around the radiator.
3. Listen carefully: Try to pinpoint where the gurgling is coming from. This can help you narrow down the source.
4. Consider a professional inspection: If you're uncomfortable working on your car's cooling system, take it to a mechanic. Ignoring a coolant system problem can lead to serious engine damage.
The combination of gurgling and the heater being on strongly points to air in the system. But a thorough inspection is necessary to rule out other potential issues.
