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Honda Civic: Why is There a Bubbling Sound When I Shut Off My Car?

The problem could be coming from the car's cooling system. Check out this step-by-step guide to learn how to diagnose and fix the bubbling sound in your Honda Civic.

By Brett Foote - April 1, 2015

This article applies to the Honda Civic/Del Sol (1992-2000).

Typically, a bubbling noise that occurs when you shut your car off is a sign of a potential problem with the car's cooling system or the exhaust. This could indicate a variety of issues, which include anything from a bad radiator cap to an incorrect mixture of water and coolant, or even a bad heater core. This is a common issue with the Honda Civics and Del Sols, so thankfully there is a lot of great information out there to help. Keep reading, and this article will run through the causes of that bubbling noise in your car.

Materials Needed

  • Funnel
  • Drip pan
  • Cooling system pressure tester

Step 1 – Check your radiator cap and coolant mixture

An improper mixture of water and coolant can lead to bubbling.

A worn radiator cap is a cheap and easy replacement, so throwing on a new one is never a bad idea. Improper mixture of coolant and water in your car's cooling system is the most common cause of a bubbling noise. Water begins to boil, which increases pressure and causes water to pass into the overflow tank. It's also possible that air is present in the system.

Bleeding the coolant system is an easy 20 to 30 minute job. Park the car on an incline, and turn the heater up to max heat. Remove the radiator cap, and pour coolant up to the base of the filler neck. Then, loosely install the cap. Start the engine, and let it run until it warms up. Turn off the engine to check the coolant level. Add coolant if necessary, and then put the cap on tightly to run the engine again, checking for leaks. Alternatively, you can rent a cooling system pressure tester from an auto parts store to test for leaks.

Figure 1. Instructions to bleed a coolant system.

If bleeding your coolant system and replacing the radiator cap doesn't fix the problem, move on to step 2.

Step 2 – Check the heater core

A bad heater core can cause a loss of fluid and various noises.

A bad heater core is harder to spot because they reside behind the dashboard, and are out of sight. Usually, you will smell coolant inside the car; however, the bubbling noise will come from the passenger's side area of the dash. Leaks in the heater core are harder to spot than those that come from a hose or the radiator. But if you are loosing coolant without any visible leaks and you can smell it inside the car, the problem is likely the core.

Figure 2. A Honda Civic heater core.

If you don't have a leak or don't smell coolant in the car, move on to step 3.

Step 3 – Check your catalytic converter and exhaust

A leaky converter can cause a bubbling noise from your exhaust.

If the bubbling noise is not coming from your dash or engine, but rather from the exhaust, then you might have a problematic catalytic converter. An exhaust leak can very easily make similar noises. Depending on the severity of the leak, these noises could occur during warm-up, under acceleration, or even the entire time the car is running. Try to pinpoint where the sound is coming from. A reputable shop should be able to easily fix a leaky pipe for you. If the sound is coming from a bad cat, you will likely have to spring for a new one.

Figure 3. A leaky exhaust can cause intermittent or constant bubbling noises.

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