How to Purge Air from an Auto's Cooling Systemby Alexis Lawrence
If you have air bubbles in your auto's cooling system, you will notice a decrease in performance in both the temperature controls inside the cabin of the car and in the cooling of the engine, which may lead to overheating. You may also notice a bubbling sound coming from your air system. When it comes to trapping air, Nissans are some of the worst offenders. The safest way to purge air from your car's cooling system is to flush the system.
Purchase a radiator fill funnel kit. The funnel kit will allow you to safely fill your radiator without spills on the engine.
Locate the radiator fill port. In most vehicles, this port is located toward the front of the engine. It will be covered by a large cap that is either black or silver. The cap will likely have a sticker on top with a warning not to remove it while it is hot. If you need help finding the port, look in your owner's manual. There should be a detailed diagram of your engine.
Place the funnel in the radiator fill port. Use a rag to open the port. If you have had the car on, the cap will be hot.
Fill the funnel with a 50/50 mix of water and coolant. Coolant can be purchased in the auto department of stores like Wal-Mart or in auto stores. Use distilled water. Well water or tap water can contain chemicals that will damage your system.
Let an entire funnel of the mixture run through the system. Liquid is heavier than air, so this will force the air pockets out of the system.
Watch the funnel. When you first put the water and coolant mixture in, air bubbles will come up into the funnel as the mixture finds air pockets inside. Once the air pockets are gone, the air bubbles should stop.
Turn the car on and put the defroster on high. When the defroster starts blowing out hot air, the water and coolant mixture has spread through the core of your cooling system.