What Causes the Coolant Light to Come on, Even in Cold Weather?

Answer: It depends on the color of the cooling system light and the kind of vehicle you’re driving.

We’ve just made it through the holiday season. And all of those Christmas lights reminded me of the multi-colored lights that can show up on your dash.

The only difference is that most of us don’t feel a sense of holiday joy when our dashboard is lit up like Clark Griswold’s house.gif of guy

A lot of newer vehicles don’t come equipped with a temperature gauge on the dash.

Some manufacturers now just use an indicator lamp that illuminates either blue, yellow, or red depending on the state of your cooling system. 

For the cooling system, each color and shape of the indicator light determines a different problem or warning. If you know what the colors mean, you’ll know where to start looking for the root of the problem. And, most importantly, how to solve it.

Now might be a good time to blow the dust off that owner’s manual and get familiar with what your vehicle’s indicator lamp looks like. Knowledge is power.

If you see a blue coolant light

This is not an emergency situation.

blue engine lightThis means your engine isn’t at operating temperature. So don’t push it too hard when you first get in to drive.

Doing so can result in rough wear and tear on the engine. Looking at you, my teenage daughter.  

Once the vehicle is warmed up this light should go out. If you’re still seeing blue after driving for several miles, you’re either driving through the Arctic or you have a problem.

You should set an appointment with your shop to see why your vehicle isn’t reaching operating temperature.

If you see a yellow coolant light

This is also not an emergency situation… yet.

yellow engine light It’s likely that your coolant level is low. Even if the level has only dropped a little, it could still trigger the sensor, depending on the vehicle.

In cooler temperatures, coolant will contract, so your best solution might be to simply top off the reservoir. 

Unfortunately, it’s more likely that your vehicle has a cooling system leak. If you’re a DIY person like me, you can check the coolant level yourself.

Just open the hood, let the engine cool (I repeat, let. the. engine. cool.) for at least an hour and then check the level.

If it’s low, you need to find the leak. Engine coolant doesn’t just evaporate in a sealed cooling system with no leaks. If the coolant is low, you have a leak. 

If you’re not the DIY type, not to worry. Checking for that leak yourself is time-consuming and risky if you don’t know what you’re doing. Just make an appointment at your shop for a cooling system inspection.

If you see a red coolant light

This IS an emergency situation.

red engine lightRed means stop. And for a reason.

If you see red, your car is overheating. This is more commonly seen in the warmer months, but can still happen in the winter.

If you see this light your car is in some (probably serious) trouble. You need to get off the roadway and shut off the engine. Immediately.

The quicker you respond when you see this light, the better chance you have of not causing permanent engine damage.

Have your vehicle towed to the nearest shop or mechanic. (Shameless plug: FREE BG On the Road roadside assistance comes with every BG service. Check with your shop to see if they offer it.)


Hot coolant can erupt, causing serious injury and burns. 

goofy car explosion gif

It’s important that no matter what is going on with your coolant, do not unscrew the cooling system fill cap when the engine is hot. (Yes, I’m saying this again.)

The more you know about your car, the safer you will be on the road. Speaking of which… Curious about the other lights that pop up on your dash? Check out my other article about what causes the oil change light to come on.

Tom Probus, Automotive Research Specialist,By Tom Probus
Automotive Research Specialist, BG Proving Ground

Tom Probus is an ASE Master Technician and has been ASE Certified for more than 20 years. He joined the BG Proving Ground in 2015, where he helps invent new equipment that keeps BG at the top of the industry.

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