The question of how to fix a car radiator leak is perhaps one of the first ones that will come to mind if you see a pond of coolant under the car.

Radiator leaks are considered one of the more serious problems regarding coolant leaks. Older cars are more prone to this fault but it can also happen to newer cars.

This article will show you a couple of ways to stop the leak or at least provide a first-aid measure until you find a more definite solution.

Leaks can also easily lead to overheating and engine damage. If you want to see what are the ten most common reasons for overheating, click here to read the article. You can also watch the YouTube video by clicking here.




This method is the most popular mainly because it’s easy to apply and fairly effective.

The application is mostly the same for every radiator sealant.

The basic principle is to pour the sealant into the coolant system, start the engine and let it run for a while so the sealant can get through the whole system.

The sealant finds its way to the puncture, starts forming a patch, and eventually seals it completely.

If everything is OK, after you stop the engine, the leak should disappear.

It all takes about 10 to 15 minutes on average and is good for smaller radiator holes or punctures.

Know that this is considered a temporary method just like a lot of the other ones we’re going to show you.

The first time you flush the coolant system, the sealant will probably disappear and the leaking will start again.




Metal parts of the radiator can be mended if the damage isn’t too serious and if it’s located in a convenient place.

The most popular methods are soldering and welding. The choice mostly depends on the material from which the radiator is made.

It’s pretty successful and if done in quality, can be a long-lasting solution.

If you’re not good at soldering or welding, I would recommend professionals for this if you want the repair to last.

A downside of this option is that you’ll seldom find a shop that specifically does this kind of repair.

One good alternative that you might find helpful is a shop that repairs refrigerators or freezers.

In this case, you’ll have to take off the car radiator yourself and take it to them, but it’s certainly worth the try.




When talking about how to fix a car radiator leak, using an epoxy sealant for fixing the plastic parts of the radiator is very effective.

Epoxy sealants are usually made of two components that are mixed together before applying them.

Also, it’s very important to clean the place where the epoxy sealant is going to be used. If not, it might easily leak again.

So, the basic principle is to clean the place where the puncture is, apply the sealant and let it dry up. Before you start, always read the instructions on the sealant to get the best and long-lasting results.

A very good option for smaller cracks on the plastic parts of the radiator. The fix can last for years if done properly.




If the crack is smaller and you happen to have some duct tape with you, you may be able to temporarily solve the problem.

Once you’ve found the crack or puncture, clean the area around as best as you can and then patch it up with the tape.

You can apply multiple layers if possible.

Be aware that this is one measure that is extremely short-lived so don’t rely on it for a further long-distance trip.

It will help a couple of miles at most before the tape adhesive starts to give in under hot coolant and pressure.




This solution for how to fix a car radiator leak is perhaps as old as the radiator leak problem. Very popular amongst drivers, especially the older generation who got out of trouble more than once using this.

The way to do this is to pour some ground pepper or coffee into the coolant system (about one or two tablespoons should be enough). After that let the engine run for at least ten to 15 minutes.

Due to circulation, the coffee or pepper will get to the damaged spot and seal it.

Sort of a cheap, homemade radiator sealant.

I can say, from personal experience that this works rather well and would definitely recommend it as a first-aid measure if you have no radiator sealant at hand. Especially if the puncture is small.

Just make sure to flush the coolant system once you’ve definitely repaired the leak.




Yes, this may seem unlikely but you can use an egg yolk to temporarily solve the problem.

The principle is the same as with ground pepper or coffee. Once you put the yolk into the system the hot coolant cooks it and small pieces of the yolk are forced into the holes or punctures.

Definitely worth the try especially if you have no other option but, by some chance have a batch of eggs in the car or a chance to buy it.

Just like with ground pepper or coffee, have in mind that you’ll have to flush the system once you’ve made the final repair. This is to get all the leftover yolk out of the coolant system.

One more thing: I would avoid the egg, pepper, and coffee if you have a modern car with high-tech systems. If you do this, you may cause a lot more damage than help.




One of the most common places where a radiator leak appears is around the coolant fan switch.

The coolant switch engages the fan once the coolant heats up to the needed temperature. Under the switch is a copper washer that may wear out or warp over time, mostly due to constant heat.

Also, overtightening when changing the switch can cause a leak. To read more about finding coolant leaks, click here.

If you conclude that this is the problem, then best flush the coolant system, take off the switch and replace the washer.

This is a pretty easy job, but on some cars, there might be accessibility issues. It might be harder to reach the coolant switch than to actually replace it.

Also, make sure the engine is cold so you don’t burn yourself.

Just don’t overtighten the coolant fan switch. You can easily damage not only the washer but also the thread on the radiator rendering it pretty much useless.




One of the tougher problems to solve when talking about how to fix a car radiator leak. Especially if the drain valve is metal.

Over time, drain valves and plugs get sort of „welded“ to the radiator due to constant heat and pressure. Scale build-up can also cause problems.

The fact that most mechanics avoid using these plugs when flushing the coolant system but rather disconnect the hose tells you enough.

If you decide to tamper with the drain valve be prepared to buy a new radiator. Lots of times it’s simply impossible to take off without damaging the radiator housing.

This goes double for older cars with higher mileage.

Best take a look at the condition of the valve before you start. If you see that it’s corroded or has a scale build-up on it, try giving it a slight budge.

If there’s no progress whatsoever or it starts bending, seriously consider buying a new radiator.




This tip goes for car radiators that have a cap on them.

In most modern cars, the radiator is sealed and the only opening is on the coolant bottle.

But you may encounter this here and there, especially on older cars.

If the cap is the problem, simply buy a new one and replace it. Try to buy a quality one so it doesn’t start causing problems again in the near future.




For the final and tenth tip on how to fix a car radiator leak. If you see that the damage is too serious and the leak is huge, best skip all of the mentioned tips and just go and replace the radiator altogether.

Yes, this is perhaps the most costly and time-consuming solution, but also the most long-lasting.

Simply, if you want to fix the leak for good and for a longer period of time this is the way to go.

On some cars (mostly older models) you can perhaps make the replacement on your own. But on newer cars, it usually involves a serious amount of dismantling and it takes a long time.

Also, make sure to buy a quality radiator so when you change it once, you don’t any future problems for a long time.


To give a final summary on how to fix a car radiator leak:

  • If the radiator leak and damage are serious, replace the radiator or other mentioned parts. It’s the best solution in the long run
  • When there’s medium damage, try to weld or solder the radiator or use epoxy sealant. If done properly, it can last for years to come and doesn’t cost as much as a new one.
  • For minimum damage use a coolant sealant. Buy one specially made for this purpose and from a quality manufacturer as these give the best results. Also, they’re easy to apply which makes them a very good solution for a leak on the road.
  • As a last resort use the home remedies such as egg yolks, grounded pepper, or coffee. They may help out but only for a short time. So if you do this, start finding an option for a repair asap.

Whatever method or option you choose, solve the problem as soon as you can. Yes, you can drive with a smaller leak for some time, but it tends to get worse very fast. Losing coolant means overheating and this can easily lead to a partial or complete engine overhaul.

So, the moment you spot the leak, inspect the problem and react as soon as possible.


Written by: Sibin Spasojevic


Former car technician, life-long car and DIY enthusiast, author for