Everybody that has done a bit of maintenance on their vehicle has accidentally overfilled their coolant tank.
Maybe you were little bit distracted when you were adding coolant into the tank and went beyond the “fill line”.
Maybe your tank is a little bit on the older side and that fill line isn’t quite as easy to spot, especially if you’re doing this project in lowlight or bad light situations.
Or maybe you just did a glug or two beyond what you were intending to, adding a little bit more coolant to the mix and hoping that you didn’t just cause a nightmare issue that has to be resolved ASAP.
Let’s find out what happens if you end up accidentally overfilling your coolant right now!
What Happens If You Overfill Coolant?
The good news is that most of the time you really don’t have all that much to worry about if you put a little bit of extra coolant into your tank.
This isn’t quite as dangerous as adding a lot of extra oil into your engine or pumping so much gas into your vehicle that it goes spilling out all over the ground.
Obviously, it’s not the best thing in the world to add too much coolant to your reservoir. You want to try and stick to the recommended amount (info about that is in your owner manual) as much as possible.
Most of the time, though, absolutely nothing is going to happen – even if you add a little bit more than just a touch extra to the tank!
You see, modern vehicles are built with coolant systems that have overflow tanks and overflow hoses built right in.
As soon the coolant system reaches its maximum pressure, any extra coolant in the tank is going to be pushed through to the overflow and then (if needed) right out that overflow hose.
It’s not ideal that excess coolant is going to be pumped out onto the ground (especially if there are pets or small children around that could get into these toxic chemicals), but most of the time it’s only going to be a quick splash and is either instantly absorbed into the surface of the road or evaporated off.
The way these tanks and hoses are designed the fluid gets pushed directly out onto the road in a quick spurt. It isn’t going to spray all over the place in your engine and (generally) isn’t going to cause a mess, either.
But in the Worst Case Scenario…
In a worst-case scenario situation, though, let’s just say that you added WAY too much coolant to your system.
Let’s say that you blew right past the initial “cold maximum fill line”, cruise beyond the “hot maximum fill line”, and brought that fluid all the way to the tippy top of your radiator cap or your overflow tank.
It’s been done before.
In this situation, the moment that you turn your vehicle on you are going to spray a flood of coolant all over the place.
The pressure is going to build to extreme levels inside of your coolant system, flooding that overflow tank with a tremendous amount of force, and sometimes blowing the overflow hose right out of its mounting bracket – allowing coolant to splash all over your engine.
If any of that coolant comes in contact with electrical components (including exposed battery terminals, wiring harnesses, etc.) you could have a serious short on your hands.
Even worse, you could cause an electrical fire under the hood of your vehicle while you are cruising down the road.
This is not the kind of situation you want to find yourself in.
How to Track Your Coolant Levels
Thankfully though, keeping track of your coolant levels is generally a pretty simple and straightforward process.
For one thing, all responsible automobile owners should be visually inspecting their engine bay every month (or every couple of months) just to be sure that everything is on the up and up.
This visual inspection should include a close look at your coolant levels, making sure that they are hovering right around that “cold fill line” that we mentioned a second above. If you are checking the vehicle after you have been driving around town for a while, though, you’ll want to be sure fluid levels are up near the “hot fill line”.
Secondly, there is a coolant level sensor built right into your radiator that lets you know if your coolant levels get to dangerously low levels.
If you see a little icon pop up on your dashboard that looks like a glowing thermometer being barely dipped into ocean waves that’s your low coolant level indicator.
This means that you have to top things up, but it also means that there’s probably a leak or some other problem with your coolant system that has to be addressed ASAP.
Do I Have to Use Coolant or Can I Use Water?
Let’s say that you are out on the highway and all of a sudden you get that low coolant symbol pop up on your dashboard – but you don’t have any coolant or antifreeze on hand.
Are you going to be able to use regular water in a pinch to keep your engine cool, to get you down the road to a service station, and not do a ton of damage to your engine along the way?
Or is that a terrible idea and you should just push your car as far down the road as possible, hoping that it doesn’t burn up, seize up, or break down somewhere on the journey?
Well, we can tell you that using water in an absolute emergency is a much better alternative than trying to force a bone dry engine down the road.
Water is going to evaporate inside of your coolant system a whole lot faster than proper coolant ever would, and that means it’s not going to give you the benefits you’re looking for – or for nearly as long as regular coolant would have.
On the flip side of things, the alternative is running things dry and allowing your engine to build up on sustainable and unsafe temperatures that will cause long-term damage to your vehicle.
In a pinch, water can work.
Just know that you’re going to need to put legitimate coolant into the car ASAP.