Bad Radiator Cap Symptoms, Test and Replacement Cost

Bad Radiator Cap Symptoms

If your car’s radiator pressure cap is broken or is malfunctioning, you will notice some bad radiator cap symptoms. In this article, we will find out what causes these symptoms, how to test the radiator cap, and how to replace it once it's starting to show signs of wear and tear.

What does a radiator cap do?

The radiator pressure cap is made up of two valves. This pressure cap keeps the coolant inside the radiator and will also make sure that pressure is maintained inside the engine's cooling system. There are different pressures for different cooling systems, but the most common is from 13 to 16 pounds per square inch with some systems reaching 1 bar. Pressure needs to be constant to ensure the flow of the chemical coolant moves effortlessly inside the cooling system.

High pressure can affect the different components of the cooling system and can lead to failure. Meanwhile, low pressure can lead to heating of the coolant leaving the system with very little to no liquid to cool the engine leading to overheating.


7 Bad Radiator Cap Symptoms

The following are signs of a bad radiator cap:

1. A pool of leaking coolant

You can easily tell that there is a leaking coolant when there's a clear fluid leaking from underneath your car along the area where the radiator is located. There are many reasons why this may have happened and the first has to be a bad radiator cap.

If the cap is stuck then high pressure can build up in the radiator and thus, the cooling liquid may burst or leak from the chamber. Also, check for holes in the radiator or if the cap is worn out or heavily damaged.

2. The presence of white streaks on the radiator

When the radiator cap leaking coolant, or cooling liquid leaks from the radiator neck it will be in liquid form but when it dries, it will leave white stains or streaks on the surface. If you have never seen coolant leaking from the cap, you can tell that this is happening because of the white stains.

These white streaks also mean that there is high pressure inside the radiator or there is intermittent pressure and the component has to be checked ASAP.

3. Coolant overflowing in the reservoir

The coolant usually goes to the reservoir area while it expands. Also, the radiator cap can release any extra pressure and send extra coolant to the overflow reservoir.

A faulty cap will release the coolant quickly and will make the reservoir overflow. You must also check if the coolant overflow chamber is working correctly. If you’re in doubt, take your car to a professional right away. 

4. Collapse of the radiator hose

If the cap is properly working, the radiator hose is round and properly inflated. But if there is increased pressure inside the hose and the vacuum is not properly released by the cap, then the radiator hose will eventually collapse to a flat material during cool down.

A collapsed radiator hose is a very serious sign that there is something wrong with the radiator cap. Check the cap if there is any damage ASAP.

5. Ballooning or bursting of the radiator hose

On the other hand, if you see that the radiator hose is inflated or ballooning then it’s likely that there is high pressure in the cooling system. An inflated hose may also start to puncture or burst and start to leak coolant all over the engine area.

When your car is old, any small hole will easily seal off just fine. When you drive, the pressure can build in the system, the pressure will eventually force the coolant through the small hole and eventually release coolant. As the radiator hose leaks, coolant will also drip from the radiator and settle on the ground.

6. Overheating engine

The cooling system will eventually run out of coolant and will make the engine very hot. If the engine becomes too hot, then turn it off. Coolant will appear under the hood as the engine cools down. Before checking the engine, let it cool down first.

7. Poor engine performance

An overheated engine will perform badly. It will become too hot to handle and may also lack performance. If you notice any engine trouble together with coolant problems, and then you should have your car engine and radiator cap checked fast.

Your engine won’t act up soon but you will notice this after a few days of overheating and overworking. Don’t wait until this happens as you may end up paying for a costly engine repair or overhaul.

Bad Radiator Cap Symptoms YouTube Video


Check and Test Radiator Cap before Replacing it

When to replace the radiator cap?

When the radiator cap is damaged in any way, it cannot properly seal the cooling system and this compromises the entire system.

Perform the following test if you have doubts that your radiator cap is acting up before replacing it.

  1. Look up the pressure rating of your type of vehicle and the pressure rating that’s printed on the pressure cap. If the values are incorrect, replace the radiator cap at once.
  2. Check the condition of the radiator cap's main seal, return seal, and pressure seal. If you see hardening, cracking or any signs of damage, replace the seals at once. Replace these with seals specified for your kind of pressure cap.
  3. Take note that the vacuum and pressure relief valves must be effortless to lift and pop back in. If there is some hesitation or you notice these are not moving flawlessly, replace the radiator cap at once. 
  4. Check the spring. If you notice that there’s no resistance and the spring no longer recoils, the faulty radiator cap must be replaced at once.
  5. Take your car to a professional repair center for a thorough checkup. A technician uses a special testing device to check the radiator cap pressure. Usually, if the radiator cap is unable to hold a specific pressure then the cap must be replaced.
  6. Don’t forget to check the radiator or the expansion tank. A faulty radiator cap will cause a build-up of pressure inside the tank which may cause cracks and leakage. If you spot any of these, replace the cap at once to prevent pressure build-up.

Radiator Cap Replacement Cost and DIY Yourself to Replace

The overall cost of radiator cap replacement depends on the type of the radiator cap and the needed pressure rating. It can be anywhere from $10 to $250. A costly pressure cap replacement includes the cooling fan assembly.

You must also consider the type of vehicle you have. The more updated your vehicle is, the costlier the replacement will be. If you have an older model vehicle, radiator cap replacement parts may be readily available and thus much easier to replace. Consider how worse your radiator replacement will be. Replacing only the cap is cheap while replacing a problematic cap, hose, and coolant reservoir can be very expensive.

Labor costs may also add to the overall cost of radiator cap replacement.  Small garages and auto repair shops may charge an affordable rate compared to large city repair shops with towering costs.

Can you troubleshoot a leaking radiator cap to save money for repair costs? Yes, you can DIY yourself to replace a busted radiator cap, but make sure to work diligently and safely.

You will need the following:

  • A pair of work gloves
  • An old hand towel
  • A pressure tester/ coolant system tester
  • A replacement radiator cap

Replace the Radiator Cap Instructions:

  1. Let the engine cool down first before you conduct a pressure test.
  2. Pop up the hood and place an old towel over the radiator cap. The towel will protect you from burns.
  3. Remove the cap by pushing this down and turning it to the left in a counterclockwise manner. Wear safety gloves to prevent burns.
  4. Take the pressure tester and screw your adapter on the tool. After securing the connection, place the radiator cap on the other end of the tester adapter. Run the tester. This is done by pumping the handle. Make sure to pump until the gauge is at 15 pounds.
  5. Check the gauge as the numbers start dropping. If this happens, you have a broken cap.
  6. Replace the old cap with the new one. Secure the new cap by turning it clockwise.
  7. Tighten the radiator cap and start your engine while the hood is popped up. You may also ask someone to start the engine for you so you can immediately check the new radiator cap.
  8. Evaluate the new cap for any discharges, bubbling, or spitting. Do this safely from a distance. If you see any bubbling, turn off your engine and reseat the radiator cap. Start your engine again to recheck.
How to replace your radiator cap safely YouTube Video

Last Words

Your car needs regular checkups and maintenance to prevent engine trouble, radiator problems, and other vehicle problems. If you suspect bad radiator cap symptoms, then don’t delay. Take your car to a specialist ASAP and have it checked for a faulty radiator cap. A bad radiator cap causes overheating so don’t delay having your car checked by a licensed car mechanic.


About the Author JamesL Davis

James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.

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