How to Fix a Faulty or Leaking Car Radiator

Part 1 of 2: Locate the leak

Materials Needed

In order to safely inspect and seal the radiator, you need a couple of basic tools:

Step 1: Locate the leak. Before you do anything el

Step 1: Locate the leak. Before you do anything else, make an attempt to locate the leak.

There are many places coolant leaks from, so you want to make sure it is actually coming from the radiator.

Step 2: Use a pressure tester. If you can’t easily

Step 2: Use a pressure tester. If you can’t easily spot the leak, you can use a pressure tester on the system.

This tool pressurises the system without the engine running, making leaks easy to spot. To use the pressure tester, attach it to the radiator or reservoir using the appropriate adapter, pumping it up to 15 PSI, which should then reveal the leak.

  • Warning: Do not exceed this pressure or damage to the cooling system may occur. Pressure testers can be rented from most auto parts stores.


Radiator Repair Techniques

Below offers three methods that you can do in order to repair a plastic radiator if the damage to it is not extensive.

  • Using a soldering iron gun to weld the plastic and seal the leak.
  • Using an epoxy that will melt after some time to seal the leak.
  • You may use both methods, solder the leak and then apply epoxy.

The first method of using a soldering iron gun can be done quickly and save on costs, especially if you already have such an item in your possession. However, the second method of using epoxy is also very easy and inexpensive. The third option of using both methods is considered an ideal one, as it will last longer compared to the other two methods.

The aforementioned techniques are simple. They require only basic skills, a soldering iron gun, and/or epoxy. Both items can be found in online stores such as Amazon and Ebay or in any hardware/tools store.

Identifying A Radiator Leak

A sign that your radiator is leaking is if a pool of green, yellow, or orange coolant shows up under your car. Sometimes all you may find are a few drops. Other times it may be an actual puddle of coolant on the road. Another sign is your temperature gauge indicating that your car is overheating.

Sometimes you may see steam rising from the radiator, indicating a pinhole leak or punctured seam. If the leak isn’t readily apparent, wash down the radiator and its hoses with water and watch for pinhole leak as the motor runs.

A word of caution when inspecting your car’s engine: parts of the motor will be extremely hot and could cause burns or scalding. Always exercise extreme caution when looking for leaks in your car’s cooling system. If you are uncomfortable checking it yourself you can always ask for help from an experienced auto radiator expert. 

Second Step: Determine the Gravity of the Issue

If you notice that the coolant is running instead of slowly dripping from your radiator, then it is likely that the leak is more severe. In this case, the damage may be too big to be repaired using a simple fix. It is important that you closely examine the leaking surface and check if there is a large crack in the reservoir or hose. If you think that the leak coming from your radiator is not that serious, then you have various options for stopping it.

Fix It With Pepper

If you notice that the coolant is gushing rather than dripping, or you can see a broken or split radiator hose, you should try a radiator hose emergency repair patch or some duct tape. But if you have a pinhole leak, which usually appears in the radiator itself, you can save the day by using the condiment that may even be in your vehicle already—ordinary table pepper.

Once your vehicle has cooled off, open the coolant filler cap and pour in as much pepper as you can find, up to a full shaker's worth is best. Start the car and let it warm up, allowing the pepper to circulate through your coolant system. With luck, the little pieces of pepper will find the pinhole and clog it right up, giving you a chance to get to the shop for a real fix. If all you've got are peppercorns, this will work, too.

Just know that this isn't a permanent solution. Not only is it unlikely to last long, you will eventually need to flush all that pepper out of your car's cooling system. Though the pepper probably won't cause any damage, it still shouldn't be floating around in your cooling system.

Safety for Repairing a Coolant/Antifreeze Leak

Working on your car can be dangerous and messy, so here’s exactly what you’ll need to ensure you don’t die, get maimed, or lose a finger and that you keep your jeans, shirt, and skin spotless—hopefully.

Repairs You May Be Able to Do Yourself if Skilled

Water Coming from the Radiator Body

If water is coming from the radiator body, then this is unfortunately bad news. It is probably finding its way through one or more pin-sized holes. The rust patch inside is typically caused by an accumulation of black sludge which can be quite extensive.

Radiators are not repairable as there are no serviceable parts inside them. You may be able to temporarily seal the leak by adding a plastic sealant to the water in the expansion tank. This is only a stop-gap solution and it will not last for long.

Water Coming From the Radiator Controls

Your radiator dashboard comprises a bleed point and a thermostatic valve. These are the only moving parts, and therefore the most likely cause of leaking if the metal casing is intact.

  • Water leaking from the bleed point. This is intended to release air from the inside that settled at the top. Bleed valves are usually at the top of radiators on the side where the water enters. Insert a cotton bud into the opening, move it around a bit, and see it if the bud is moist you when you remove it.

If the bud tip is moist, engage the bleed key with the screw, and try to turn it clockwise to see if you can tighten it. If it tightens then the valve was loose and you may have found the cause for your radiator leak.

  • Water leaking from the thermostatic valve. This is a somewhat more complicated component. It controls the temperature in the room by regulating the flow of water entering the radiator.

It slows the flow down, and then stops it as the radiator reaches the desired point, and then allows more water to flow when the radiator starts cooling again. As might be expected this radiator valve can start leaking at various points.

The spindle at the heart of the control knob has a plug of wax attached to the valve control via a pin. This is responsive to temperature and expands and contracts accordingly. It is most likely to leak at the midpoint of the setting.

If you suspect it is leaking, call a gas safe-registered technician because they will know what to do. First, they will drain the radiator below the level of the leak. Next, they will close both the supply valve and the lock valve, making sure to note the number of turns the latter takes.

It is important to reopen the lock valve to the same setting after repairing or replacing the spindle. We cannot recommend this task to an inexperienced person. This is because the whole system may require re-balancing if they reset the lock valve to the wrong position.

First, our gas safe, registered technician will undo the union nut, and bleed the radiator of any remaining water / air in the valve body. Then, they will wrap PFTE tape around the main end of the valve a sufficient number of turns.

Finally, they will tighten the union nut, open the supply and lock valves, and restore the water in the radiator to fully commission it and put it back in service.

  • Water Coming from the Screw Couplings on the Pipes

Finally, cast your eye over the remaining couplings to the radiator to check for any leaks. If you do find one, turn off the system and allow it to cool before attempting retightening. Once the metal in the pipes and couplings has cooled and they have contracted, you will find tightening them is easier.

Why do car radiators fail?

The main reason for radiator failure is a coolant leak, which can lead to the cooling system failing.

If the coolant has not been checked or topped up properly, the radiator, hoses and hose connections will become clogged and begin to rust. Over time, such corrosion will cause small holes or ‘pinhole leaks’ to develop in the car radiator. This will result in engine coolant loss, and a need for car radiator repair – or even the complete replacement of your radiator.

What Are the Colors of a Radiator Leak?

The coolant in most older vehicles is green, while some modern vehicles may have coolant that is orange, pink or blue. Coolant should be handled with care, as it is poisonous to humans and animals if ingested and can harm the environment and waterways. If you see a fluid of any color leaking from your vehicle, it is important to determine where it is coming from and stop the leak.

How to use radiator stop leak

Using K-Seal as a radiator stop leak is simple:

  1. Shake the bottle.
  2. Put radiator stop leak in the coolant reservoir or radiator.
  3. Run the engine up to operating temperature.

The liquid formula will make its way around the engine and fill any pinhole leaks, holes and cracks in your radiator or cooling system to fix it, permanently. And thanks to its scientifically tested formula, there is no risk that this radiator stop leak will cause overheating.

How to Fix a Radiator Leak

Knowing how to fix a radiator leak involves learning your options and then choosing the right one for you. You should know that the most popular—and easiest—way to fix a radiator leak is to use a stop-leak product that you simply pour into the radiator. For example, AlumAseal Radiator Stop Leak & Conditioner can quickly fill any small holes in the cooling system. Once you pour it in, you can check your coolant level and top it off if necessary, and then get on with your day—knowing your radiator leak has been fixed!

If you don’t have any stop-leak products on hand when you notice the radiator leak, there are a couple of alternative ways to temporarily stop the leak so you can safely drive to the store to get some. One option is to use egg yolks. This may sound odd, but the eggs will congeal enough to seal tiny leaks, and the effect should last long enough for you to get ahold of a better option, like AlumAseal. Just note that you have to separate the egg whites from the yolks of about four eggs, and then pour just the yolks into the cooling system. Then start your engine to help the eggs go far enough in the system and start to congeal.

Note that black pepper will have the same effect, since if you pour about half a pepper shaker’s worth of this substance into the cooling system, it will seal the leak. Just keep in mind that both eggs and black pepper are temporary fixes and should never be used as a permanent way to stop a radiator leak. They should allow you just enough time to pick up a stop-leak product so you can fix the issue.

Of course, some radiator leaks require more serious help that only a mechanic can provide. For instance, if you check for leaks and see that your coolant is running out of your radiator, not just dripping, it may be time to take your car to the repair shop. But for most radiator leaks, a simple stop-leak product should take care of the problem!


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