How to Change Your Engine Coolant (and Burp the Air Out)

First, the safety part — this one's serious

• Never open a hot cooling system. When the engine is warm the system is pressurized and the coolant is above boiling — cracking the cap can spray scalding coolant everywhere. Wait until the engine is completely cold before you open anything.
• Coolant is toxic. Ethylene glycol tastes sweet, which makes it dangerous to pets and kids — wipe up spills, and store it sealed and out of reach.
• Work on level ground so you can fill and bleed it accurately.

Why change it

Coolant does two jobs: it lowers the freezing point and raises the boiling point of the water in your engine, and — just as important — it carries corrosion inhibitors that protect the water pump, radiator, and the metal passages inside the engine. Those inhibitors deplete over time; once they do, corrosion and scale build up, which leads to overheating and a failed water pump. That's why coolant is a time-and-mileage item, with an interval that varies a lot by type.

Use the right coolant — don't mix types

This is the part people get wrong. There are a few families of coolant and they aren't all compatible — mix the wrong ones and they can gel and clog the system:

• IAT — old-school green, shorter life, older vehicles.
• OAT — extended-life, in various colors (GM Dex-Cool orange, VW/Audi G13 pink, Toyota SLLC pink, Mopar OAT purple).
• HOAT — hybrid, often yellow or turquoise.

Use exactly what your manufacturer specifies — the types aren't interchangeable just because two look similar, so don't go by color alone. Not sure what yours takes? BoxKitz lists the coolant type per engine. Buy either pre-mixed 50/50 (easiest) or concentrate you mix 50/50 with distilled water — never tap water, whose minerals scale up the system.

Drain it

1. With the engine cold, put a drain pan under the radiator and open the radiator drain (petcock) at the bottom corner — usually a plastic wing-nut or plug. Opening the cap up top lets it drain faster.
2. Let it drain fully. Some engines also have a block drain on the side of the engine block — draining that too removes more of the old coolant (check your manual).
3. Close the drain(s) back up.

Flush (optional, but worth it)

If the old coolant is rusty or dirty, run a flush: fill with distilled water (or a cooling-system flush product), run the engine to temperature with the heater on, let it cool, and drain again. Repeat until it runs clear.

Refill — then get the air out

This is the step that separates a good coolant change from an overheating headache. As you fill, air gets trapped in the high spots of the system, and an air pocket will make the engine run hot and the heater blow cold.

1. Fill the radiator/reservoir slowly with your correct 50/50 coolant.
2. Burp the air out. The cleanest way is a no-spill (spill-free) coolant funnel that threads onto the filler neck — it holds a column of coolant above the system so air can rise out and be replaced as you idle. Many cars also have bleeder valves you crack open to let air escape.
3. With the funnel on (or the cap off, depending on the car), run the engine to operating temperature with the heater set to full hot. Let the thermostat open — you'll see the level drop and bubbles rise as the air works out. Top up as it drops, and a gentle squeeze of the upper radiator hose helps push pockets out.
4. When it stops bubbling and the level holds, remove the funnel, set the reservoir to the cold/full line, and cap it.

Some vehicles are notorious for trapping air and need a specific bleed procedure — check your manual if yours is one.

Check it

Let it cool, then check the level and look for leaks at the drains and hoses. Recheck the reservoir after a couple of heat-up/cool-down cycles and top up to the cold line if needed. A cheap coolant tester confirms your freeze protection is where it should be.

Dispose of the old coolant properly

Used coolant is toxic and hazardous — never pour it on the ground or down a drain. Collect it in a sealed container and take it to a recycler:

• Auto parts stores — many take used coolant (Advance Auto and NAPA often have a coolant container next to the oil one). Heads-up: AutoZone does not accept antifreeze, so call ahead.
• Municipal eco-stations / household-hazardous-waste depots take it.
• In Canada, provincial used-oil-and-antifreeze programs cover it (in Alberta, the same ARMA network that handles used oil). In the US, search Earth911 for a local drop-off.

The bottom line

Fresh coolant with fresh inhibitors is cheap protection for some of the most expensive-to-fix parts on your engine. Just respect the three rules that make coolant different from oil: only ever open it cold, use exactly the coolant your car specifies, and get the air out before you trust it.

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