How to Check and Top Off Your Coolant

Learn the proper way to check and fill your coolant.

The antifreeze coolant that flows through your car or truck’s cooling system does more than just keep your engine from freezing in the winter. It also cools the engine while you’re driving.

Without coolant, your engine would overheat after only a few minutes of driving, or it could freeze overnight.

There are two things you should remember when you’re checking and topping off your antifreeze: the level and mix ratio. Discover the right way to do these with Blain’s Farm & Fleet.

Coolant Level

Always make sure your coolant is full. If it’s not, add a little more to top it off. Make sure your engine is cold when you check your antifreeze. Auto cooling systems are pressurized, and the fluid is very hot after the engine has been running.

To check your coolant, open your hood and look for a whitish, opaque plastic reservoir. It should say “engine coolant” on the side or on the cap. And it should have markings to tell you when the coolant is full or low.

Usually, you can see through the plastic reservoir. So you can tell if your coolant is low or not without even taking the cap off.

Just to be safe, you should also remove the radiator cap and make sure your radiator is full of antifreeze, too. Check your antifreeze at least once every two weeks.

If you need to add some coolant every time you check it, you probably have a leak in your coolant system. Have your car or truck inspected as soon as possible.

Antifreeze Mix Ratio

Most people think that antifreeze is all there is to coolant. As long as you keep your coolant reservoir and radiator full of the (not always) green liquid, you’re good, right? Not necessarily.

Besides antifreeze, the coolant in your car or truck should have distilled water in it, as well. Even if your coolant reservoir and radiator are full, you still need to make sure you have the right water to antifreeze ratio.

The mix should be half antifreeze, half water. Having too much water will not cool the engine as well as a 50-50 mix, as antifreeze has a higher boiling point than water.

But having too much antifreeze could cause your water pump to fail. Since antifreeze is much thicker than water, your water pump has to work twice as hard to pump pure antifreeze than it does a 50-50 mix.

You can buy pre-mixed 50-50 coolant, or you can buy full-strength antifreeze and mix it with water yourself. There’s no way to tell exactly what the mix of your antifreeze is unless you flush your cooling system and make sure to refill it with a 50-50 mix.

You can, however, make sure your coolant has a low enough freezing point for winter by using a coolant tester. This is especially helpful if you live somewhere that gets colder in the winter. You may need more antifreeze than water to avoid freezing.

For more vehicle guides and how-tos, check out our Maintenance & Repair Blog.