Your car's radiator cap may seem like a not-so-important component under the hood. But without one, all hell will break loose inside the radiator. See, this part prevents water and coolant leaks from the radiator and relieves pressure once the coolant temperature gets too high. Now because of the nature of its job, this cap is designed to withstand huge amounts of pressure and exposure to extreme heat. However, it will eventually wear out after years of use. Once this cap malfunctions, coolant will leak out from the radiator. This can then put the engine at risk of overheating. So to avoid more serious car problems a busted cap can cause, here are some tips when dealing with common radiator cap problems:
1. Corrosion - No matter how durable the cap is, it will eventually corrode because it's regularly exposed to harsh chemicals and water.
Symptoms: You'll know a cap is corroded if the rubber seals aren't preventing leaks, and the plunger gets stuck.
Solution: When dealing with small rusty patches under the cap, get your hands on a steel wool and some anti-rust solvent. Brush the corroded patches away until you get a clean, rust-free surface. However, if the cap has corroded beyond repair, it's time to get a new one.
2. Stuck plunger - Over time, grime and engine debris can clog the mechanisms under the radiator cap. When this happens, the plunger can get stuck, stopping the cap from preventing the coolant and water from boiling over.
Symptoms: Whenever the coolant or water boils over and reaches the cap, it goes up from the radiator and is transferred to another chamber so it won't flow out. If the boiling liquid won't flow into another chamber, it means the cap plunger is jammed.
Solution: In many cases, a stuck plunger means you need to clean the cap and possibly replace the spring underneath.
3. Worn-out seals - Just like any rubber component, seals will lose their elasticity over time. They can also warp when they've reached the end of their lifespan.
Symptoms: Once the seals wear out, the liquid inside the radiator will easily flow out, contaminating nearby components. If you see leaks outside the radiator cap, chances are that the seals are broken.
Solution: Unfortunately, seals can't be repaired or reused. Your only option is to get replacements.
4. Cracked cap - Usually made of plastic, the cap can crack over time, which could then lead to a leak.
Symptoms: Obvious signs are liquid pooling around the cap and cracks or holes on the cap's surface.
Solution: Because replacements are cheap, it's best to just get a new one once the old cap cracks.
Other troubleshooting tips
Before you fix or change a radiator cap because you suspect a cap leak, make sure that you have determined that the leak isn't coming from the radiator tubes. Over time, the radiator pipes can wear out, causing the liquid inside to leak. If this is the case, you can temporarily plug holes with a sealant. But eventually, you'll have to get a new radiator.