A radiator cap is a small part used to seal a vehicle’s cooling system and control its pressure. You will find this cap on the radiator or coolant reservoir. The primary function of radiator cap is to remove excess heat from an automobile engine.
But what if this small cap in your car goes bad? Can a faulty radiator cap cause overheating? Today, we will answer these questions & tell you what a failed radiator cap can do to a vehicle cooling system & its engine.
Can a Bad Radiator Cap Cause Overheating?
Yes, a bad radiator cap can make your car engine overheat. A good-quality cap always keeps the cooling system at the right pressure. As a result, coolant liquid will not boil or turn into steam. However, a faulty radiator cap can fail to hold pressure.
So what happens if radiator cap does not hold pressure? You will notice coolant boil sooner, create air or vapor pockets and can escape from the system. Overall, this will decrease the coolant level and lead to engine overheating. The situation can become worse if the car is working hard or when it’s hot outside.
Is it possible that radiator hose collapses due to faulty radiator cap? A defective radiator cap in your vehicle can cause a radiator hose to collapse. In fact, many automotive experts say that a faulty radiator cap is one of the most common reasons behind collapsed radiator hose. Because its vacuum valve can fail to let coolant flow back from the overflow tank after the engine cools down.
Does a Defective or Broken Radiator Cap Cause Coolant Loss?
A weak radiator cap can allow coolant to escape from the system. The main job of this cap is to seal the cooling system and keep the pressure at the right level. In standard passenger cars, the safe pressure rating of the normal radiator cap is around 13 to 16 psi. This pressure increases the coolant’s boiling point.
But if cap breaks and its pressure relief valve is not working properly. Then coolant will escape or boil too early, which can lower overall coolant level.
Also read: Can an incorrect radiator cap cause coolant loss?
What Does a Faulty Radiator Cap Look Like?
How to know if radiator cap is bad? A malfunctioning radiator cap will show clear and noticeable physical signs of damage. For example: you will notice cracked seals, rust, corrosion or damage around the cap. Further, the cap can leave dry, crusty, white residue, dried green or orange coolant near the radiator opening.
You will find a hard and cracked rubber seal on the bottom of cap. Moreover, corrosion on metal parts, spring or edges of the cap also indicate a failed radiator cap. The spring will also feel loose or stuck if you press it.
Bad Radiator Cap Symptoms
Generally, you will observe these common signs in your car cooling setup if your radiator cap starts to fail.
- Engine overheating
- Coolant loss
- Coolant leaks
- Low coolant level
- Collapsed radiator hose
- Coolant overflow
- White or crusty coolant residue
- Radiator hose bursts
- Steam from engine
- Air inside cooling system
- Bubbling or foam in radiator
How Often Does a Radiator Cap Go Bad?
A standard radiator cap can last for 3 to 5 years. This is approximately 30000 to 50000 miles. Over time, the rubber seal can dry out and the spring inside the cap can become weak. We recommend you replace the cap whenever you flush or service the cooling system of your vehicle.
If you change the cap before it completely fails, you can avoid cooling system problems. However, some radiator caps have a service life of 7 to 10 years. Therefore, they can stay in good condition for a long time if you only drive your car for your normal daily routine.
Can I Drive With Bad Radiator Cap?
We strongly recommend you to avoid driving with a damaged radiator cap. Because it can put your vehicle’s engine at risk. So, you should replace it as soon as possible before your trip. A faulty cap can cause coolant to escape and overheat the engine. Further, severe overheating can damage the engine as well as warp the cylinder head or harm head gasket.
How long can you drive with a bad radiator cap? As we suggest, you should not drive with a faulty cap. Suppose you are in an emergency and have no other choice or you need to reach a mechanic.
Only in this situation, you can drive a very short distance such as a few minutes or a couple of miles. Our advice is to keep your vehicle speed low as much as possible and watch the temperature gauge closely when you are driving.
What Happens When a Radiator Cap Fails?
- Mainly, a defective radiator cap can make your car overheat plus lead to serious problems such as blown head gaskets & cracked engine blocks.
- The cap will fail to keep the cooling system at correct pressure.
- Due to too much pressure, you will face severe harm to parts of your car cooling setup.
- There is the high possibility air can enter the cooling system if the cap fails to maintain a proper seal. This can badly affect coolant flow.
- In case of very low pressure, the engine coolant can boil sooner and escape from the system.
- You will see the overflow tank overfilled if the cap sends too much coolant into the reservoir.
- Further, low coolant levels can make it harder for the engine to stay cool.
- If you ignore a worn radiator cap problem and keep driving without fixing it, then overheating can completely damage your car engine.
Helpful: Will you see a hot temperature reading if your car radiator cap causes the coolant to boil?
How To Test Radiator Cap At Home?
Step 1: First of all, you should check pressure rating printed on your car radiator cap. Then compare it with your vehicle’s service manual.
Step 2: You must clean cap plus radiator filler neck to remove dirt or dried coolant.
Step 3: Now you can attach the radiator cap to a pressure tester with the correct adapter.
Step 4: Always make sure the tester seals properly. Otherwise, a dry or poorly fitted seal can cause air to escape and give you a false result.
Step 5: You need to pump the radiator pressure tester until it reaches the pressure rating of the radiator cap.
Step 6: At this point, you should watch the pressure gauge to see if the cap holds the required pressure. Remember, a faulty cap will lose pressure quickly.
Step 7: Also confirm if the cap releases pressure at its specified pressure rating. Also, the cap should hold normal pressure and release excess pressure if needed.
Step 8: Our recommendation is to replace the radiator cap if it cannot hold the correct pressure or releases pressure too early or too late.
How To Fix a Bad Radiator Cap?
Generally, you cannot repair or fix a malfunctioning radiator cap. The reason is, it contains parts such as a spring, pressure valve & rubber seal. They can wear out or lose their proper pressure control if you try to repair the cap.
Our advice is very straightforward in this matter. We think replacement of the radiator cap is the best solution. For this, you should let the engine cool completely before you remove the old cap. Never forget to check the radiator filler neck for dirt, rust or damage. After that, you can install a new cap with the correct pressure rating.
How much does it cost to fix a faulty radiator cap?
If you buy a radiator cap yourself from an auto parts store, it can cost you around $5 to $15. But if you are someone who prefers a mechanic to handle car repairs, then a local mechanic will charge for the radiator cap plus a small labor fee. So, the total expense can be approx. 20 US dollars.
Wrapping It Up
Radiator cap is a small component, but we cannot deny this fact that a minor fault in it can affect the whole cooling system. We advise you to check the cap for cracks and replace in case it cannot hold pressure.
But if a bad radiator cap has already damaged radiator hose, then you also need to replace it right away. RONTEIX is a top supplier of quality silicone coolant hoses. If you want to order premium hoses or you have further inquiries about this topic, then you can send us a message anytime.
People Also Ask
Can a New Radiator Cap Be Bad?
Yes, this is a fact that a brand new radiator cap can still be faulty. Common reasons include manufacturing defects, wrong pressure rating for your vehicle or a damaged rubber seal from shipping.
Why is My Car Still Overheating After I Replaced the Radiator Cap?
A new radiator cap will only fix overheating if it is due to pressure loss or coolant boiling over. If your car still overheats, the other reasons can be a bad thermostat, faulty cooling fan, damaged water pump or blown head gasket.
Should You Remove the Radiator Cap if Your Car Engine Overheats?
No, you should never remove radiator cap if the engine is hot or overheating. The cooling system can hold high pressure and hot coolant/steam can spray out suddenly. It can cause serious burns.
Can a Loose Radiator Cap Damage Engine?
Yes, a loose radiator cap can harm a vehicle engine. The cap keeps the cooling system under pressure. If the cap stays loose, the system will lose pressure. This can lead to overheating, blown head gasket or warped cylinder heads.
Why Does My Car Overheat When Idling?
If you notice that your car overheats only when idling or sitting in traffic, it means the cooling system does not get enough airflow. Common causes include a faulty radiator fan, bad radiator cap, a stuck thermostat or a weak water pump.
More Helpful References:
Can a bad radiator cap or thermostat cause overheating – Facebook
Analysis of Causes of Engine Overheating due to Cooling System Failure Using Pareto Principle
