Coolant leaks are one of the most common car mishaps that a driver can encounter.
Because the whole system is under constant pressure and is subdued to huge variations in temperature, it’s only logical that it will fail over time.
If this does happen, hopefully, this article will help you find and repair this problem with less time, nerves, and perhaps money.
In this article, you can read about the symptoms, common locations for leaks, probable solutions, and other topics regarding coolant leaks.
WHAT HAPPENS WHEN COOLANT LEAKS APPEAR?
Once coolant leaks appear, the coolant level in the system goes down.
When the level goes down, overheating is next in line.
Overheating then leads to minor or major engine damage. This can cause big problems and expenses.
Coolant leaks are one of those car mishaps that will make a lot of trouble from a minor malfunction (for instance a loose clamp of 1 Euro may lead to an engine overhaul of a couple of hundred or even thousands of Euros.
So tend to a leak problem as soon as possible, regardless of malfunction difficulty.
If you don’t have any prior knowledge of how the car coolant system works, click here for a great explanation on Wikipedia. This may additionally help in finding a coolant leak.
MAIN TYPES OF COOLANT LEAKS
These are divided into two main categories:
External coolant leaks
External coolant leaks are mainly visible ones. As the term says, they happen on the outer side of the coolant system and are noticed mostly by leaks, moisture, or oxidation traces around the coolant system elements.
Internal coolant leaks
These are leaks that happen inside the engine.
As you probably know, coolant runs through the engine block.
As oil is also present as an engine liquid, coolant and oil have to be separated. This is done by separate engine canals for cooling and lubricating and most important by gaskets.
Internal leaks are mostly recognizable by the symptoms they give off which are mentioned lower in the article.
HOW TO FIND A COOLANT LEAK?
Coolant leaks are notorious for being hard to find.
In my own experience, seldom does the leak show right away. It usually ends up in a long and tedious search for the location.
Additional difficulties are caused by false leak traces; leaks spilling from one place on to another (like a gasket leak spilling on a hose which can have you thinking that the hose is the problem, not the gasket).
Anyway, here are the most common methods of finding coolant leaks:
This method is by far the most popular, especially with external leaks. Everyone (including mechanics) will first take a look under the hood of what may be wrong.
I would recommend this method first. So, once you notice that the coolant level is low make a brief inspection of the parts of the coolant system which are most exposed (coolant hoses, clamps, radiator, connections, etc).
You should look for various tell-tale signs of which the most obvious will be small puddles of water in various crescents of the engine block, moisture “stains” or oxidation traces.
Coolant leaks tend to leave oxidation marks wherever the leak is occurring. Over time they build up giving you a good clue to where the leak is.
Best use a flashlight or some other source of light as today’s engine bays are crammed making most of the coolant system hard to reach and less visible.
Also, make a check under the car for puddles of coolant.
Pressurizing the system
Coolant leaks mostly happen when the engine is hot.
But making a proper inspection with a hot engine is almost impossible and dangerous.
So, a cool engine would be best, but coolant leaks, in most cases, don’t appear when the engine is cold.
This is why a method of pressurizing the system was invented.
By pressurizing the system, leaks should appear however hidden they may be.
This is mostly done by specialized tools that can be bought for a fair amount of money.
Not a bad solution if the leak is very hard to find and you’re ready to spend some extra bucks on tools.
Good old hear-say combined with the power of the internet can provide a quality solution for your problem.
Since coolant leaks can be pretty hard to find, getting additional information can save time and money.
Also, some car models have weak spots on the coolant system that are notorious for failing (poor quality gaskets, coolant hoses, faulty engineering solutions to begin with, and so on).
Whatever the case may be, before you start pulling apart things and embarking on a coolant leak search, go on the internet and type your problem. You’ll be surprised at how many people might have had the same trouble.
Maybe a friend or a family member had the same car problems. Don’t be shy to make a phone call.
On the internet part, I would highly recommend specialized forums as they are worth gold. Most forums are divided by car brands and are easy to find.
Trust me, better more time on the internet or the phone than under the hood in a wild goose chase.
Following the symptoms
This mostly goes for internal leaks as the main fault is not visible (leaks happens inside the engine).
On this part, you simply have to follow the breadcrumbs to get home.
Most symptoms that occur with internal coolant leaks give off clear and dramatic symptoms, leaving little place for second-guessing (white smoke, oil-coolant sludge mixture in the coolant bottle, etc).
More about these symptoms lower in the article.
Patience and logic
Patience is key to finding a coolant leak. If you’re nervous best leave the job to someone else.
Face the fact that it may take hours if not days of searching, observing, and testing to find the leak. Thanks to today’s crammed engine bays a lot of painstaking dismantling may also be needed.
Thinking logically is also a huge benefit. Where might a weak spot be, did something happen that could lead to a leak, and so on.
Patience and clear thinking is a powerful tool for any car repair, especially coolant leaks.
SOME MAIN SYMPTOMS OF COOLANT LEAKS
CONSTANT LOW LEVEL OF COOLANT IN THE COOLANT BOTTLE
This is the first and most obvious tell-tale sign of a coolant leak.
If the level is frequently low even after adding coolant, then you have a problem.
On some cars, there is a cap on the radiator where you can also inspect the coolant level and see if everything is OK.
Of course, to spot the problem on time, you have to check the coolant level regularly.
If you want to learn how to do this, click here for a separate article on that topic.
Once the coolant level falls under the minimum, the system is not able to cool down the engine.
This then leads to overheating.
The first signs will be if the temperature gauge shows above-normal temperature or the coolant level warning light goes on.
If this does happen, pull aside as soon as possible and make an inspection (coolant level, leaks, etc.)
If you’re interested in what are the most common reasons for an overheating car, click here to read a separate article on that topic.
PUDDLES OF COOLANT UNDER THE CAR
For most drivers looking under the car is somewhat an awkward habit. At best, most drivers tend to make a regular oil and coolant check and that’s it.
But a casual look under the car may come in handy, especially regarding coolant leaks.
When you notice that the coolant level is low, take a look under the car.
If there are puddles and leak traces on the plastic undercarriage cover, you have a coolant leak for sure.
COOLANT INSIDE THE PASSENGER CABIN
Rare case but does happen, mostly in older cars.
These kinds of leaks are mostly recognized by a puddle appearing on the co-drivers side.
If this is the case, best take a sample of the fluid on your fingers and smell it.
This is to avoid possible confusion if the leak comes from the outside (for instance rainwater, when washing the car or else). Coolant has a characteristic odor of its own.
The main reason for this is a damaged heater core or hoses that lead to it.
WHITE SMOKE COMING OUT OF THE EXHAUST
Once you start the car and it heats up and white smoke starts to come out of the exhaust, you have a coolant leak problem.
The main reason would be a faulty intake manifold gasket.
But although the symptoms are pretty scary (white smoke, possible misfiring of the engine, etc), in most cases it’s not that much of a fuss.
I mean it does include more serious engine repair but is considered a pretty regular maintenance job (of course depending on the car model).
MIXTURE OF OIL AND COOLANT IN THE COOLANT RESERVOIR
This case is perhaps most severe and costly.
Usually happens if the engine has been overheating numerous times.
Best recognized by a sludge-like substance that forms inside the coolant reservoir (coolant bottle).
The main reason for this is a damaged (blown) head gasket. The purpose of a head gasket is to separate the oil canals from the coolant canals in the engine.
If the engine overheats, the gasket warps or breaks thus causing oil and coolant to mix.
If this happens, a semi engine overhaul is imminent. This means taking off the cylinder head, replacing the gasket, machine leveling of the cylinder head, etc.
MOST COMMON REASONS FOR COOLANT LEAKS
DAMAGED COOLANT HOSE
Coolant hoses are constantly exposed to severe heat and pressure.
Over time, these factors cause material fatigue and the coolant hose ruptures or breaks causing coolant leaks.
Also, a common cause is a physical damage (like accidental damage when work is done around the engine).
LOOSE HOSE CLAMPS
Clamps hold the hoses in place tightly, preventing coolant leaks.
They fail mostly due to material fatigue or physical damage.
Hose clamps also tend to get loose because of hose shrinkage.
Over time, hoses tend to shrink due to constant change in temperature.
LOOSE OR FAULTY COOLANT BOTTLE CAP OR RADIATOR CAP
Most drivers neglect the fact that the coolant bottle cap is also an expendable part.
They have their life span and although it is long, the cap should be changed at least at 200.000 km or so.
A faulty cap-seal is usually the main problem.
Faulty caps will let coolant evaporate and may let excessive air get into the system.
A tricky reason, as it can mislead you into searching other parts of the system for coolant leaks.
DAMAGED COOLANT RADIATOR
The coolant radiator has the main role of cooling the system down.
In short, it consists of small metal pipes integrated into a sort of metal “honeycomb”.
Radiators have their life span. It’s usually long (for at least 200,000 km without any problems).
The main reasons for damaged car radiators will be material fatigue (due to high temperatures and pressure) or physical damage.
Best recognized by leaks, moisture, and oxidation traces on the coolant radiator itself.
DAMAGED WATER PUMP
Water pumps are engine-driven pumps which, in short, consist of a small turbine that propels the coolant around the system.
The parts of the water pump that can cause coolant leaks are faulty shaft seals and faulty gaskets.
In more rare cases, the water pump housing can crack.
If this happens, you’ll probably see leaks under the car and moisture around the water pump.
DAMAGED FREEZE PLUGS
As the name says, its main intention is to (in case of coolant or water freezing) release pressure to the engine block.
They also have the purpose of letting out left-over coolant or water which is why they are located on lower parts of the engine block.
Don’t know if you’re aware, but freezing coolant or water expands at a high rate. So much so that it can crack the engine block.
Problems mostly occur when the freeze plugs are either damaged or improperly mounted.
FROZEN COOLANT OR WATER IN THE SYSTEM
If you haven’t checked your coolant before the winter season, there is a good probability that it can freeze.
If water is in the system, then it will freeze for sure.
When either of these two starts to freeze, ice forms inside the engine block and starts to expand.
More ice forming means more expansion which can eventually lead to a crack in the engine block.
A crack means a leak.
These kinds of leaks are mostly visible once you start the engine and it heats up.
They are usually small, barely visible cracks that can be hard to find.
Making a coolant antifreeze check on time is the best prevention and solution here.
If you want to learn how to make this check, click here for a written tutorial or watch it on our YouTube channel.
BAD SEALING OF THE THERMO SWITCH
Thermo switches are electrical switches that turn on the coolant ventilator.
They are triggered by temperature and are located on the radiator itself.
This is also a part that is a common cause of problems. Like other switches, it simply wears out over time.
Besides the electrical problem, one more common problem is the copper washer that seals the thermo-switch to the radiator. Due to frequent temperature changes, the washer warps and coolant leaks start to appear.
One more common cause is physical damage: when replacing it, people tend to over tighten thus damaging the thread. This again leads to coolant leaks.
DAMAGED HEATER CORE
Besides the standard coolant radiator, all cars have one more radiator, also known as the core heater.
Core heaters have the task of heating the passenger cabin. It’s connected to the rest of the coolant system by hoses that enter the passenger cabin.
It’s located, in most cases on the co-drivers side.
Over time, due to material fatigue, they start to leak. Also, a known problem is damaged hoses that lead to the core heater or loose hose clamps.
DAMAGED HEAD GASKET
We’ve previously mentioned that the main purpose of the head gasket is to separate oil and coolant inside the engine.
Once the head gasket is damaged (broken or warped), coolant leaks into the engine oil canals thus mixing coolant and oil.
The main reason for this mishap is the massive overheating of the engine, once or multiple times.
FAULTY INTAKE MANIFOLD GASKETS
Intake manifold gaskets also fail over time, mostly due to material fatigue.
Once they do, coolant leaks may appear.
All depending on the car model, not that complicated to replace.
OTHER FAULTY SEALS AND GASKETS ON THE COOLANT SYSTEM
Besides mentioning all of the most critical parts that can cause coolant leaks, you should also pay attention to all parts of the coolant system that have seals and gaskets on them.
I’m talking about all of the hose-to-engine connections, hose-to-hose connections, thermostat housing gaskets, etc.
All of these should be considered when looking for coolant leaks.
IMPROPER WORK AROUND THE COOLANT SYSTEM
If you’ve had work and repair done around the coolant system in the recent past and coolant leaks are starting to occur a re-check of the whole job is the first thing to do.
Common mistakes are loose hose clamps, hoses that are not properly mounted and fixed, poorly set gaskets, and so on.
HOW TO MAKE A COOLANT LEAK FIX?
We’ll go in the same order as with the symptoms:
DAMAGED COOLANT HOSE
Replacement is the only solution here. Any kind of improvisation like mending, taping up, or else is short-lived and lasts only till the coolant heats up at best.
All depending on the location of the hose and its accessibility, this can be in most cases a DIY job (loosen the hose clamps, budge the hose on both sides until they move, remove the coolant hose, mount a new one, and tighten the clamps).
Coolant hoses are molded and shaped to a specific size for various car models. Just ask for your car model at the car parts shop or even better bring the damaged one with you. Also, ask for quality coolant hoses so you don’t have to change them again soon.
LOOSE HOSE CLAMP
If you see moisture or a coolant leak near a hose clamp (like where the hose is connected to the radiator, where the hose is connected to the thermostat housing etc), it’s common practice to first try to tighten the clamp.
It’s usually done by a screwdriver or a ratchet. Even combined pliers can help.
Check that the clamp is not physically damaged. If it is, best replace the clamp completely.
Again, depending on the accessibility, replacing or tightening a hose clamp is well within the DIY realm.
LOOSE OR FAULTY COOLANT CAP OR RADIATOR CAP
Always check that the coolant bottle cap or radiator cap is firmly tightened.
If you conclude that the cap is faulty, best buy a new one.
They are fairly cheap to buy so need for improvisations. Best buy the same as the previous one for perfect sealing.
DAMAGED COOLANT RADIATOR
Damaged coolant radiators can be fixed in two main ways:
Completely replaced with a new one
This is perhaps the best solution. Radiators have their life span and once it’s finished, problems will become more frequent. When you install a new one and in quality, forget about coolant leaks regarding the radiator for a long time.
Mending is mostly done if you don’t have enough money to buy a new one or the radiator type is not widely available (older car models, old-timers, rare brands of cars on your market, or else).
If you find the right repair shop, this fix can serve for a reasonable amount of time (even up to a couple of years). Just have in mind that every repair of this kind is meant to hold the boat afloat until you buy a new one.
I would recommend this only as an emergency remedy, not a solution.
On both of these methods, I would recommend a DIY solution only If you have some serious experience around cars.
The main problem here is getting to the car radiator, rather than replacing it.
DAMAGED WATER PUMP
If you’ve concluded that the water pump is causing a coolant leak problem, it should be replaced as soon as possible.
In most types of engine designs, the water pump is mounted inside the engine block and is driven by the timing belt.
This means that the leaking coolant can get on the timing belt and cause it to slip which can lead to major engine damage.
Replacing the water pump is a complicated repair and is best left to professional mechanics.
DAMAGED AND LEAKING FREEZE PLUGS
With these, it all depends on the level and location of the damage.
If the freeze plug itself is damaged (thread or head of the screw), just buy a new one and screw it in.
If the thread in the engine block is damaged, then that’s a bigger problem.
In that case, although a simple repair on its own, accessibility is the main issue here. This problem can even lead to things like having to take the engine out.
This is the main reason why cap-like freeze plugs are much better as they are simply “hammered” into place.
If the freeze plug is the problem and the accessibility is good, you should be able to change it on your own.
If the thread on the engine block is damaged, best leave it to a mechanic to solve the problem.
FROZEN COOLANT OR WATER IN THE SYSTEM
As mentioned, frozen coolant or leftover water in the system can cause serious damage in the form of engine block cracks.
Cracks mean either a complete engine replacement or removing the engine and trying to mend the crack.
Mending is done with special welding procedures. To tell you truth, from what I’ve seen, not a very long-lived solution.
BAD SEALING OF THE THERMO SWITCH
The main reason for this may be a copper washer under the thermo-switch. Either this or a damaged thread on the radiator (where the thermo-switch is screwed in).
If the copper washer is the problem, the thermo-switch is simply removed and the washer replaced with a new one. Fairly easy job to do if you have good accessibility.
Engine block threads are considered a bigger problem as they usually mean replacing the whole car radiator.
DAMAGED CORE HEATER CORE OR HOSES THAT LEAD TO THE HEATER CORE
Heater cores are considered a more complicated repair for one reason only: they are very hard to access in most cars.
The main reason of damage here is material fatigue.
Heater cores are located deep under the dashboard which means a lot of dismantling of inner plastic panels, trimming, and else to gain access.
Once you’ve gained access, the replacement is fairly easy. The same goes if you have a damaged hose.
Patience is key here if you want to make this a DIY job. The dismantling and putting together everything is, on most car models, painstaking.
If you don’t have the patience, best leave it alone.
DAMAGED-BLOWN HEAD GASKET
This is the most severe and costly problem of them all.
A blown head gasket means a semi engine overhaul (taking off the cylinder head, machine leveling of the cylinder head and engine block, replacement of the gasket, etc).
All in all, the next worst thing to a complete engine overhaul.
No DIY possibilities here whatsoever unless you’re a professional mechanic.
If this happens, best find a good and trustworthy mechanic to do the job as these repairs have to be done in a quality manner.
FAULTY INTAKE MANIFOLD GASKETS
These are less complicated than a blown head gasket.
Includes taking apart the intake manifold and replacing the gasket.
Unless you have some serious experience around cars, don’t try to do it on your own.
OTHER FAULTY SEALS AND GASKETS OF THE COOLANT SYSTEM
As mentioned, every other seal and gasket regarding the coolant system should be checked.
If there is a problem, the main issue can be accessibility. Gaskets and sealants are, in most cases not that complicated to repair if you can reach them.
Easy-to-access gaskets can be easily replaced and are considered a DIY job.
On the other hand, you may have a car model that will need a lot of dismantling of the surrounding parts to gain access.
When this is the case, best leave it to a professional mechanic.
IMPROPER WORK AROUND THE COOLANT SYSTEM
If you’ve repaired yourself, re-check that everything is OK.
If a mechanic repaired, visit him/her and let them re-check the job.
Poorly set gaskets, seals, bad fittings, loose clamps are a common mistake when making repairs of coolant leaks.
HOW MUCH DOES A COOLANT LEAK FIX COST?
External coolant leaks
Coolant leaks of this type involve coolant hoses, hose clamps, various gaskets, seals, and others.
Prices stated below heavily vary from country to country, depending on the availability of a certain car model, average prices on the market, etc.
I’ve taken prices in my country and I hope it will give you some orientation:
Coolant hoses cost from 10 Euros to about 50 Euros per piece, all depending on the car model and what hose is damaged (longer, shorter, rare or widespread, etc.)
Hose clamps are a couple of cents to a couple of Euros max.
Coolant bottle caps and radiator caps vary from 5-10 Euros per piece
Coolant radiators are pretty expensive and are sold in various classes of quality, again depending on the car model and brand that you’re buying. Copies go from about 50 Euros a piece al the way to a couple of hundred Euros for brand name radiators.
Freeze plugs are essentially screws and aren’t that expensive. Usually up to 10 Euros per piece. The bigger problem here is to find the proper one (in terms of size, length, and thread), especially for more rare cars or old-timers.
Various gaskets, seals, and fittings (apart from the head gasket and intake manifold gasket): these are pretty cheap to buy; prices go from 5 Euros up to about 20 Euros per piece, again heavily depending on the car model and brand name.
As you can conclude, external coolant leaks are not pricey to replace in terms of money.
What you should consider is the price of labor. Many leaks are hard to find and once found, demand a lot of dismantling thanks to crammed engine bays.
This takes time and time is money if a mechanic is going to do the job for you.
If you’re going to let a mechanic do the job, rather consider the price of labor as a concern than the price of parts.
Internal coolant leaks
On this part, be ready to file for bankruptcy…..just kidding.
But, when faced with this kind of repair be prepared for some serious expenses.
Prices vary from 20 Euros to about 100 Euros per piece. In this case, the pump is not that expensive, labor is. As mentioned, the water pump is driven by the timing belt on most engines. This means dismantling the timing belt mechanism to replace the pump. Essentially, two jobs have to be done. Labor is the main cost here, in my opinion.
Intake manifold gasket
Gaskets themselves are pretty cheap, even the brand name ones won’t set you off for a couple of dozen Euros. Getting to it is the main problem.
Most cars demand a lot of work and dismantling to get to it. Again, consider the price of labor rather than the gasket price.
Blown or damaged head gasket
This is by far the most expensive problem. As mentioned a partial engine overhaul has to be done.
This means opening the engine (taking off the cylinder head, machine leveling of the head and engine block, perhaps changing valve seals, etc).
With today’s engine designs (lots of bits and bobs on them), taking off the cylinder head is a hard task let alone the rest of the job. This means, besides pricey parts, pricey labor also.
Prices for the whole job start from 300 Euros up to a couple of 1000 Euros for more premium cars. Also, the car has to be left in the shop for a few days.
Rarely does this job end without extra expenses as some other parts will probably need replacement (gaskets, bolts, belts, etc).
SHOULD YOU USE COOLANT LEAK SEALERS?
Ahhhh yes…..the magic solution….that’s what we all want when faced with coolant leaks and possible expenses.
TV commercials, car parts shops, gas stations, coolant leak sealers can be found pretty much everywhere.
They’re sold as a liquid that dissolves in the coolant, “finds” the leak, and seals it up. Sounds pretty good.
But in practice, it is nothing more than a temporary solution and should be seen that way. It will last, at best a couple e of months or until the next coolant change.
To be more precise: use it in case of emergency (on the road, if you can’t repair, the mechanic doesn’t work, a part is not available, etc) and solve the main problem as soon as possible.
Also, this is only useful for small punctures or damages. If the coolant leak is big, this won’t help at all.
These substances tend to stick to the coolant canals inside the engine block possibly causing future problems when the real repair is done.
I’ve used these myself and all that I can say is that it helped for a while but until I rolled up my sleeves and did the repair, I didn’t solve the problem.
HOW LONG CAN YOU DRIVE WITH A COOLANT LEAK?
For small coolant leaks, you can drive days, weeks, even months. No damage just as long as you refill the coolant.
Major coolant leaks; best not drive at all. You’ll be out of coolant in a matter of minutes, causing overheating and damage to the engine.
Internal coolant leaks: once you’ve noticed the problem, it would be, of course, ideal to stop driving right away.
But, in many cases, this will not be possible. To tell you the truth you can continue driving.
White smoke coming out of the exhaust or sludge appearing in the coolant bottle (in less quantity) can’t stop you from driving. In the beginning phase of the malfunction, the temperature will go up a bit and that’s it.
In later phases, when the malfunction worsens, you can cause damage to the engine.
All in all, solve coolant leaks as possible. More driving with this malfunction means more risk of causing major engine damage.