Every vehicle on the planet relies on multiple systems to keep temperatures under control.

Air cooling, oil cooling, and full-blown coolant systems all work in combination with one another to make sure that your vehicle is never operating at unsafe temperatures.

And while all three of these systems have a big role to play in temperature control, the bulk of the heavy lifting for keeping your vehicle within safe temperature levels is the actual coolant system.

Coolant (sometimes called antifreeze) gets added into a rubber or plastic reservoir, it gets pushed through rubber hoses throughout the engine bay to absorb heat and excess temperatures, gets run through a radiator to expel all of that heat, and then rinses and repeats the process all over again.

Keeping the system running smoothly is a huge piece of the puzzle to keeping your vehicle running smoothly.

But what if you start to see bubbles in your coolant tank?

Is that a surefire sign of something serious about to happen to your vehicle (an expensive fix that you might not be prepared for)?

Or is it simply the way the system has been designed and nothing to worry about at all?

Find out right now!

There Are Bubbles in Coolant Reservoir – Is That Bad?

The overwhelming majority of modern vehicle coolant systems are designed to operate under pressure.

This means that the whole system is a “closed system”, with no external air making its way into the coolant component when it’s working correctly.

If you see bubbles in your coolant reservoir that’s almost always a sign that something isn’t quite right.

It means that air is getting into an otherwise closed system, and that means that the system itself has become compromised.

Now, that being said, sometimes bubbles in the reservoir are a really minor issue that can be addressed in no time and with next to no extra money out of pocket.

Sometimes, though, those bubbles are a sign and symptom of something much more serious that’s gone wrong under the hood. Something you have to address right away or it could mean your car seizing up and breaking down on the side of the highway.

What Causes Coolant Reservoir Bubbles

Let’s run through all of the common causes that could be producing bubbles to pop up inside of your coolant reservoir.

Pockets of Air in Your Reservoir

For starters, the most common reason that you’re getting bubbles in your coolant reservoir is simply because tiny little pockets of air have been locked inside the coolant system.

It’s not unusual for these little pockets to get trapped every time you flush your system, or even every time you add new coolant to your reservoir.

As you drive along the road and the sealed system builds up pressure – and the coolant starts to heat – all of that air expands in gets forced back through the system into the reservoir itself. Then you start to see the bubbles pop up and explode.

It’s not the end of the world if it’s just pockets of air in the coolant reservoir.

This is almost always an issue that sorts itself out.

Failing Radiator or Reservoir Cap

The cap on your radiator or reservoir might not look like that important a part of your vehicle, but the role it plays is huge.

You see, this component is responsible for pressurizing the rest of the system every time you fire your vehicle up.

If the cap isn’t working the way that it is supposed to (especially if it becomes old, cracked, or compromised) it’s going to let a lot of extra air into the system that is supposed to be closed and pressurized.

This usually produces a “boiling reservoir” kind of condition, letting you know that way too much air is flowing into the closed system – to the point where the engine can overheat.

Sometimes you won’t even be able to start your vehicle if the part has become significantly compromised. You won’t be able to create a pressurized vacuum when you are turning the ignition, and that means that your car is going to be sitting in the driveway or parking lot completely dead (all because of a three dollar to five dollar part).

A Thermostat About to Go

A bad thermostat in your cooling system can cause all kinds of headaches, not the least of which is a lot of extra air to build up inside of your coolant system.

Your thermostat is supposed to open and close at a specific temperature setting, either letting coolant flow through the engine area or directing it into the radiator to cool the coolant itself back down.

If the thermostat is on the fritz it isn’t going to open or close the way it should.

This is going to produce a bubbler affect inside of your reservoir and it’s a sign that you need to swap this core part out ASAP.

Head Gaskets That Are Failing

If there’s one problem that you don’t want to be the root cause of bubbles in your coolant reservoir it’s this one.

Head gaskets are pretty strong and pretty durable, but they are known to dry out, crack, and become compromised – particularly in high mileage vehicles that haven’t been all that well maintained.

If your head gasket goes then combustion gases from your cylinder are going to slip directly into the cylinder head, forcing their way into your coolant system (which is supposed to be closed) and filling it with a lot of air.

You’ll know that something is squarely with your head gasket if bubbles start to pop up just as soon as you turn your vehicle on.

Another way to know that your head gasket is cracked or leaking is to check your dipstick. If the oil looks like it is kind of milky (bubbly and white) it means that the head gasket is leaking into the oil as well.

Head gaskets are super expensive to repair, sometimes totaling vehicles. Fingers crossed you don’t have to knock this out in the future.