How to Check Your Car's Coolant System

Mia Bevacqua
June 21, 2018


Cooling system problems can easily kill your car’s engine. This means checking your coolant level and condition on a regular basis is essential, and it becomes even more critical during those hot summer stretches.

But don’t sweat — it’s not that hard to do.

It’s a good idea to check your engine coolant — which is a mix of antifreeze and water — at least once a month. And, as always, it’s crucial to keep up with your car’s routine maintenance, which includes periodic coolant changes.

Let’s go over how to check the coolant and what to look for while you’re under the hood.

Locate and remove the radiator or reservoir cap

Make sure the engine is cold: This is the first and most important step. Opening the cooling system on a hot engine can make coolant burst from the radiator, seriously scalding you. Make sure the car has been resting for a while — in fact, it’s best to check the coolant after the vehicle has been sitting overnight.

Remove the cooling system cap: Most cars have a cap on top of the radiator, but on some vehicles, the radiator is sealed. In this case, the pressure cap will be on the coolant reservoir. If you’re uncertain, check your owner’s manual to find out where it is.

Analyze the coolant

Determine your vehicle’s coolant type: In the past, almost all vehicle’s used green, inorganic additive technology (IAT) coolant. These days, manufacturers employ a variety of types, each with a unique color. It’s not uncommon to find blue, red, yellow or pink coolant. Check your owner’s manual to determine the correct kind for your car.

These are some of the common coolant types, colors, and applications:

  • Green, IAT coolant: older vehicles
  • Orange, organic acid technology (OAT) coolant: General Motors, Saab, Volkswagen
  • Yellow, hybrid OAT: Ford, Chrysler, European
  • Turquoise, phosphate-free hybrid OAT (HOAT): BMW, Volvo, Tesla, Mini
  • Pink or blue, phosphate HOAT: Toyota, Nissan, Honda, Hyundai, Kia
  • Purple, silicate HOAT: Mercedes-Benz, Audi, Volkswagen, Porsche

Check the coolant level: If the car has a radiator cap, the coolant level should reach the top of the radiator neck. In instances where the car only has a reservoir, the level should reach the “cold full” mark stamped on it. 

A low coolant level indicates a leak somewhere. In most cases, the system will need to be pressure tested with a special tool to determine the source of the problem. Then it can be repaired.

Check the coolant condition: No matter what color it is, coolant should be translucent and free of contamination. If not, there’s a problem.

Coolant that’s rusty or has things floating in it is extremely dirty. In this case, at a bare minimum, the cooling system will need to be flushed. In extreme instances, components may need to be removed and cleaned or replaced.

Milky, pink coolant is a sign that transmission fluid has gotten into the cooling system. A broken transmission cooler is almost always the cause. When this happens, the radiator will need to be replaced, and the cooling system flushed. The transmission should also be inspected to see if it has been contaminated by the intermixed fluid.

Coolant that’s been contaminated by oil is a sign of a serious engine problem, such as a bad head gasket or leaking intake manifold. A professional can diagnose the source of the issue and repair it.

A buildup of brown junk can indicate the system has been contaminated with radiator stop leak, if you’ve used it. When this happens, at a bare minimum, the cooling system will need to be flushed. We recommend never using stop-leak substances because they are likely to eventually fail, costing you more money. 

» LEARN MORE: Get an estimate for a coolant change or flush

Check the hoses and clamps

In addition to checking the coolant level, you can also take a close look at the system's hoses and clamps. If the rubber hoses look worn out, cracked or especially grimy, consider having them replaced.

The clamps on the end of the hoses also need some attention. These clamps can loosen over time due to engine vibration. It's a good idea to check them on a regular basis to ensure they are holding the hose on as designed. Most of the time you can make adjustments to these clamps either using a flathead screwdriver or a pair of pliers. Just make sure the engine is off and cold before you work on anything.

If you don't feel comfortable checking your car's coolant system yourself, take it to a certified mechanic. Just about any shop can perform a simple coolant system check.

Don't want to do it yourself?

Regular coolant service is important

Regardless of what the coolant looks like, your vehicle’s cooling system should be serviced per the manufacturer's maintenance schedule. The interval for your car can be found in the owner’s manual. Many cars made in the last couple decades don’t require a coolant exchange until 100,000 or 150,000 miles.

Performing a coolant service or flush is best left to a professional. This is primarily because air enters the cooling system during procedure, which can cause your engine to overheat if the air isn’t bled out. Experts often use a special “vacuum-fill” tool to extract air from the coolant after the service.


Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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