Overfilling coolant in a car might not seem like much of a concern. But, depending on how much extra you add, it could lead to almost immediate issues.
In short, it’s not necessarily dangerous to you, the driver, but it will quickly damage your engine and vehicle. It could also be fatal to anyone or anything ingesting leaking antifreeze.
Don’t take the chance, even if it’s only slightly above the ‘MAX’ mark. It’s there for a reason.
Curious to know more about overfilling car coolant?
In this extensive guide, I will explain everything you need to know about overflowing coolant.
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What Is Coolant?
Coolant is the name for a combined mixture of water and antifreeze. It flows through your engine, removing heat. This is then dissipated into the atmosphere at the radiator.
Every internal combustion engine requires a cooling system. Currently, most engines used in automobiles are ‘water-cooled’ and need coolant.
Like everything on a car, you must maintain coolant levels in the sealed system. Too little, and there won’t be enough to cool your engine. Too much, and the system will overpressurize.
What Is The Coolant Tank?
You’ll notice a coolant tank in your engine bay. It’ll be filled with a tinted liquid and usually has a revealing label (like ‘Engine Coolant’) and a warning icon.
Look at your owner’s manual to find out which container has your coolant. You’ll see a diagram with labels.
This tank is known as a coolant reservoir, recovery tank, or overflow tank. It allows the system to remain sealed and pressurized while still providing room for the liquid to expand slightly.
Older models have expansion tanks designed to expel surplus pressure to the atmosphere instead. Cars don’t do this anymore for (very understandable!) ecological reasons.
Note: although most cars have reservoirs nowadays, people still use the expression ‘expansion tank’ to refer to it.
You must always be wary when opening the coolant tank or radiator cap. Because the system is pressurized, steam and hot water vapor will fly out when it’s blistering.
Before opening the cap to top your coolant up, wait for the engine to cool. Then, cover it with a heavy cloth. This way, you’ll protect yourself from potentially severe scalds.
How Much Coolant Is Too Much?
Your coolant levels should be between the ‘minimum’ and ‘maximum’ marks. Your vehicle might use different terms (‘Full’/’Empty’, ‘MAX’/’MIN’, ‘F’/’E’, etc.).
These levels typically refer to the vehicle being chilly. Again, you can check this in the owner’s manual.
You’re all good if the coolant levels are between these two marks. If it’s at all higher, you have too much.
Simple.
What Happens If I Accidentally Overfill My Coolant?
The system will become overloaded if you accidentally overfill your car’s coolant tank.
You can expect to see the following symptoms. The severity, and the speed with which they develop, will depend on how badly you’ve overfilled the coolant.
You’ll need to remove some coolant from the system to reduce it to a safe amount.
Coolant Leaks
When the pressure within the coolant system is extreme, it puts too much stress on each individual part.
As an example, the clamps and tubes are made to fit a specific amount of pressure. This is also true for the water pump, radiator, radiator cover, seals, and more.
Coolant could seep through at any vulnerable point.
You’ll see your coolant levels have dropped when you come to examine them. You might also observe:
- White streaks in the engine bay
- A sweet aroma coming from the front of your car when it’s running
- Overheating
- A puddle underneath your engine (if left running)
Failing Coolant System Components
As mentioned above, the additional burden on the system might make components fail or operate below peak performance.
The most probable weak points are:
- Hoses – watch for brittle rubber, cracks, and bulges
- Clamps and seals – can you see any new evidence of coolant leakage? A few old streaks aren’t unusual.
- Radiator cap – is there evidence of white drip marks or evaporation when the engine’s hot and running?
You might also find a problem with the radiator itself or the water pump.
Any damaged or faulty coolant components need to be replaced.
How Do You Remove Coolant From The System?
So, you’ve overfilled your refrigerant? Oops!
No worries, though! It’s straightforward enough to remove.
Here are a few suggestions on what to do next.
Call For A Mobile Mechanic
You could call a mobile mechanic if you’re worried about removing coolant from your system.
In most cases, there’s no need – a companion or relative can likely offer as much assistance (for free).
A mobile mechanic is an expensive option, too.
They’ll use a suction pump (as below) to carefully remove enough coolant until it’s safe.
Although it’ll only cost a few dollars in labor rates, there’ll be an additional callout fee. It’s best to avoid this, if feasible. This isn’t a complex job and requires no professional skills.
Use A Gentle Suction Pump
At most automotive hardware stores, you’ll find some kind of manual vacuum pump. A basic turkey baster or sizable syringe would also work.
Stick this in the coolant reservoir and remove as much fluid as necessary. (Don’t forget to throw it away or keep it in the garage as a tool from now on!)
It’s usually a wise idea to stop at the ‘MAX’ mark. That way, you’ll know if the levels are going down.
These simple plastic tools shouldn’t cost you any more than $10.
Ensure you dispose of the coolant lawfully, following local environmental regulations. You’d typically need to head to a recycling center of some sort.
Completely Drain The System
This is completely unnecessary, but it is an option if none of the others are available.
It might be a wise idea if you’re due for a coolant flush anyway.
You or a mechanic will simply wait until the engine’s chilly. They’ll then remove a clamp and hose at the bottom of the engine and drain the coolant into a container.
The hose then gets reattached, and the coolant is topped up from the beginning.
Can You Drive With Too Much Coolant?
No – you shouldn’t run your car if the coolant levels are over ‘MAX’.
In reality, you’d likely get away with it. Probably! Not definitely! Driving carefully and at low loads to your nearby hardware store or mechanic should be permissible.
But it’s not worth the peril! It’ll take a matter of two minutes to remedy this issue. When the repair is so simple, why would you drive?
Ask a friend to pick something up from the hardware store for you. Alternatively, if you can wait a day, order something on Amazon. It doesn’t need to be anything too fancy.
Properly disposing of the coolant should be vital on your agenda, though. If you haven’t run the car yet, keep it in a safe storage container, ready for use at your next top-up.
Conclusion: Is Too Much Coolant Dangerous?
The coolant system is sealed and pressurized (‘closed’). It’s designed to operate at a specific psi (between 13 and 16 – or about 1 bar – usually).
Anything above or below the expected normal pressure will be detrimental. Depending on the severity, you might see instant problems, or they could take some time to develop.
Leaks and overflows onto the ground could also be lethally toxic to animals (including pets) and even children. You must completely clean up any leaks immediately (without washing it down the drain!).
If you’ve overfilled your coolant, don’t panic! Avoid turning your engine on. Follow the simple steps above to remove it; your car will be as good as new.
