Your car’s cooling system is what keeps the engine working at optimal temperatures. It circulates coolant through the engine block, drawing away heat before circulating it through the radiator to cool it down.
The process is repeated endlessly as long as your engine is running. Despite the hard work, many car owners rarely give the cooling system a second thought. This is because a good cooling system can keep at its job for tens of thousands of miles.
It’s a closed system. The coolant shouldn’t disappear, and you shouldn’t worry about it unless your car is overheating or the levels drop.
Is it Normal for My Coolant Level to Drop?
Even though your cooling system runs in a closed-loop, the system isn’t entirely leakproof. As the coolant moves between the engine block, the radiator, and the reservoir bottle, there are chances of losing a portion of it – especially if it vaporizes.
A perfectly normal car will lose around a quarter of an inch of coolant level in four months. The level drop will be much lower if your cooling system doesn’t work that hard to keep your car within optimal temperatures.
This drop is so minimal to the extent that you will still have coolant between the MAX and MIN levels in your reservoir within a year.
Losses faster than this could hint at some trouble within the cooling system.
Why Does My Car Keep Losing Coolant?
If you are losing more than the normal amount of coolant, it’s time to be worried. The biggest indicators that you’ve got to check your cooling system are:
- A pool of colored fluid that resembles your coolant on the surface after you park your car for a while
- An overheating car
- A massive drop in coolant level (inspect the coolant tank to notice)
As a rule of thumb, you should first top up your coolant tank and observe your car for at least a week before deciding to continue troubleshooting or not. Sometimes, your car will naturally burn more coolant if you push it hard (like towing heavy stuff or driving hard up hills.)
Check the coolant levels a couple of times in a day after the top-up. If it keeps dropping, then it’s time to check out the following possibilities.
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An Overfilled Cooling System
While the MIN and MAX lines in modern reservoir (overflow) bottles are hard to miss, some overenthusiastic and uninformed car owners are tempted to top up the coolant bottle past this level.
This is common when you are losing coolant. You feel that adding some more past the MAX line will give you more wiggle room.
This is detrimental. A cooling system works under pressure. It needs that remaining space for expansion when the car heats up.
If you overfill the overflow reservoir, the cooling system will pressurize beyond specification, forcing the vent outlet to open and release some pressure.
- The released pressure contains some vaporized coolant, and this could lead to dropped coolant levels.
- The same could happen if your push your car too hard or drive it when it’s faulty:
- Driving too long in hot weather
- Overloading the car
- Driving too fast up steep hills
- A clogged radiator that doesn’t cool the system fast enough
- Using the wrong coolant
Takeaway: Always use the recommended coolant and fill it to the MAX line – never beyond it. Check and top up your coolant level after frequent driving like heavy towing or driving with the car fully loaded for long.
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A Loose Reservoir Cap
After filling up your coolant, you might be tempted to stop screwing on the reservoir cap before it’s fully seated on. After all, the risk of the coolant sloshing out doesn’t seem real.
The problem is a loose reservoir cap won’t hold in pressurized coolant vapor once the car heats up. If the cap is too loose, you will hear some hissing sound or even see some steam from beneath your hood when the car heats up.
Takeaway: Screw your reservoir cap on firmly until you can’t turn it anymore. Ensure the threads are well lined up for a firm fit and to avoid stripping them.
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A Faulty Reservoir Cap
Your reservoir cap could also cause problems if it doesn’t form a perfect fit over the mouth of the reservoir. This could be because it’s old and its rubber seal or pressure release system is damaged.
A damaged reservoir cap will have the same problems as a loose cap. It won’t form a tight enough seal, and evaporated coolant will wisp past.
If you can hear a hiss when your engine is hot and track it to your reservoir cap, replace it. You could first try tightening it to ensure that it isn’t loose.
At times, its threads could be stripped after screwing it wrong. If you’re lucky, replacing the cap only could fix the problem. Sometimes, you might have to replace the bottle, too if its threads are damaged.
Takeaway: Replace a damaged and leaky reservoir cap. It’s not good enough to keep the coolant within the system once things heat up.
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A Cracked or Leaking Reservoir Bottle
Most modern reservoir bottles are plastic. Over time, the plastic expands and contracts as the car heats and cools. This could make the plastic brittle and susceptible to cracks.
Moreover, you could get cracks if involved in an accident – especially if your reservoir is mounted to the front of the car.
Cracks and holes in the tank could lead to vapor loss when the system is hot or actual coolant loss when the car is cold.
Here are some signs I witnessed when my car had a cracked reservoir bottle
- I found a pool of coolant under the car exactly below the coolant reservoir
- The coolant level was consistently dropping to a given level overnight without driving the car
- There were coolant stains on the body of the vehicle around where the coolant bottle is installed
Buying a replacement reservoir bottle is the best way out. It’s hard to repair plastic that endures constant expansion and contraction.
How to Seal a Cracked Coolant Reservoir Bottle
Some people will avoid replacing a coolant reservoir bottle and opt to seal up the cracks. You can do this using some heat-resistant sealant or two-part epoxy.
Remember to scuff up the bottle around the crack and apply the sealant onto a dry surface.
However, from experience, I have learned that such a seal will wiggle loose sooner than later. Sometimes, you’ll be back to square zero after four hours of driving.
Takeaway: Spend the extra bucks and buy a replacement bottle. Don’t bother repairing the cracks.
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Damaged and Worn Radiator Hoses
If you’ve come this far and haven’t identified your leaky part of the puzzle, you could move on and check your coolant hoses. Inspect them for any cracks. You can identify cracks by seeing wet spots on the hoses or coolant drops below them.
I was inspecting the car while it’s hot is a good way to identify such mistakes. You should also check the points hoses join with other components and tighten the clips around the places.
Finding leaks on hoses can be hard. However, be patient and inspect every hose, especially if you are dealing with an old car.
Takeaway: If you find a leaky hose, buy a replacement and install it. Don’t bother splicing or repairing the cracks. Again, the pressure will get to the patch blowing it open.
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A Leaky Radiator
Any small pinhole leaks in your radiator will lead to coolant fluid level drops. While these might not be seen when the car is cold, you could get a whiff of moist, sweet smell rising from the radiator.
You will see colored smears under or on the radiator that resemble your coolant fluid if you are keen.
Sometimes, you might see signs of corrosion or clean spots since the coolant might evaporate as soon as it leaks out. This is radiator discoloration.
Takeaway: Just like any other part of the cooling system, repairing a leaking radiator is a temporary fix. The wailed will come loose sooner or later. The only safe and permanent solution would be replacing the radiator.
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A Damaged Heater Core
A car’s heater core is part of the air conditioning system that pulls heat from the engine and circulates it around the car to keep temperatures up. This means that a portion of your engine coolant runs through the heater core for heat exchange.
If the core is leaking, some coolants will be lost when you turn on the heat or use your defroster.
In this case, you will experience scenarios like:
A Sweet Smell in the Car
Your car’s coolant releases a sweat odor when heated. If you detect a lovely smell in the car that isn’t your air freshener, chances are the heater core is leaking. Look beneath the dashboard.
If the smell gets stronger as you move towards the heater core, it’s a problem.
Sometimes, you might find a pool of coolant in the car just below the heat exchanger.
Your Car Blows Cold Air Even When the Engine is Hot
If your AC still blows cold air even after the engine has heated up, chances are the heater core isn’t doing its job right. This accompanied by unexplained coolant level leaks could hint at a leaking heater core.
The Final Check – Pressure Leak Check
If you’ve gone through all these checks and haven’t identified a leak yet, you could go a step further before moving on to possible problem #8.
A compression test pressurizes different parts of the cooling system and checks for pressure drops after a while. A drop indicates a leak in that section of the system.
The test could help you identify another easier fix to the problem before pulling the trigger on fixing internal leaks.
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Internal Leaks
Finally, if you haven’t identified a problem and still have a leak, you should face the fact that you’re perhaps facing an internal coolant leak.
This happens when some of your coolants leak into the combustion chamber and burns together with your fuel.
Fixing internal leaks can be really expensive. They are labor-intensive and involve disassembling the engine to some extent. Some common internal leaks include:
A Blown Head Gasket
A head gasket forms the seal between your engine’s cylinder block and cylinder head. The gasket prevents coolant and oil from leaking into cylinders or to the outside.
A blown gasket will let coolant seep out onto the engine block or into the combustion chamber.
What Causes Blown Head Gaskets?
Your car’s engine gets very hot when working. If the heat goes beyond the threshold, the extreme expansion, shrinking, and warping of the metals surpass specifications. This could rub out the head gasket damaging it.
Signs That You Have a Bad Head Gasket
A bad head gasket will let coolant into your cylinders. Apart from leading to unexplained coolant loss, it could also show symptoms lie:
- An overheating engine
- Milky white coloration in the oil
- Oil residue in the coolant
- White smoke coming from the tailpipe
- Bubbling in the coolant reservoir and radiator
- Streaks of oil and coolant streaming down the gasket
- Loss in engine power if the gasket damage leads to lowered cylinder compression
If you experience any of the above problems, in addition to an unexplained coolant leak, you should consider getting your head gasket replaced. You can DIY if you have the experience or get some professional mechanics to handle it.
A Fractured Cylinder Head
A cracked cylinder head could also cause your coolant levels to drop over time. Cylinder heads crack due to overheating, head gasket failure, or restricted coolant flow.
Other signs of a fractured cylinder head include:
- A drop in oil levels
- Reduced engine performance
- A lot of smoke from the exhaust
You can buy a new cylinder head or have the current one repaired and reconditioned.
Other possible causes for internal leaks include:
- Damaged Cylinder Bores
- A Manifold Leak
- A Hydraulic Lock
How Do You Temporarily Fix a Coolant Leak?
If you don’t have a leaky bottle or hoses, you could get away with using a leak stop additive with your coolant. Something like Alum-A-Seal or Bar’s Leak could stop pinhole leaks in your radiator.
Other coolant sealers like K-Seal could plug up tiny blemishes on your head gasket or cylinder heads.
Remember that coolant leak sealers are not a permanent fix. They will slow the flow or plug a slight loss but won’t make it go away permanently.
You can use them as you look for money to address the root cause of the coolant leak.
Why is My Car Losing Coolant But Not Overheating?
Sometimes, you can lose coolant but still not overheat your car. Even though the cooling system won’t be working at its best, it might still be good enough to keep your car cool under prevailing weather conditions and use case.
Don’t keep driving like that, though. Chances are, your coolant level will keep dropping, leaving your car exposed. There is also the possibility the car will overheat when pushed harder, for instance, when loaded, driven for long, or used in a long traffic jam.
What Happens if Coolant is Below Minimum?
If you are wondering how long you can drive with low coolant, the answer depends. You can run the car for a few days if the level is above the minimum mark.
However, you should stop and refill as soon as the level drops below the minimum mark. You risk overheating and knocking on your car if you keep driving with the coolant levels that low.
Can I Add Coolant to My Car?
Yes. You can. Try to use the same coolant as what you already have in the car. Ensure that you get ready to use coolant. If you buy a concentrate, don’t forget to dilute it in a 50/50 mixture with distilled water.
Avoid mixing different coolant brands unless you are sure their chemical composition is compatible. Drain existing coolant and dispose it before filling up the system with a new batch.
It’s good practice to flash your car’s cooling system and fill it up with a new batch of the recommended coolant once you identify and fix the cause of the leak.
Can I Put Water In My Radiator?
While adding water into your radiator isn’t advisable, it’s better to have water than run on low in an emergency. Remember to have the radiator flushed once you get to a mechanic and fill it with the right coolant.
You should only use water in an absolute emergency. Moreover, ensure that the water is as clean as possible. Distilled water would be ideal as it has no minerals. If you don’t have it, only top up with water, you feel safe drinking yourself.
How Often Should I Change Coolant?
While coolant levels could stay fixed for years in a good system, you still have to change it now and then. Flushing the system every 30000 miles is good practice. Some manufacturers recommend changing it every 60000 miles.
Will Removing my Thermostat Fix a Leak?
Some mechanics would recommend removing your car’s thermostat to fix minute leaks or cases of overheating in your car.
This isn’t advisable, especially if you live in cold places. Your car might never reach optimal operating temperatures without a thermostat controlling it. This is detrimental to the engine.
Check this too: Car AC Troubleshooting & How-To Guide
However, you could get away with removing a thermostat if you live in a very hot climate. The absence of a thermostat might make the system run under lower pressure, making it more tolerant of slow coolant leaks.
Replacing a faulty thermostat and troubleshooting leaks are more responsible than pulling out your thermostat.
Bottom Line
If your coolant levels are dropping at an alarming rate, start troubleshooting and repairing simple problems first. Keep an open mind and avoid being fixated on common problems.
Don’t forget to do a compression check and rule out any other leakage causes before resorting to fixing internal leaks.