How to Put Antifreeze in a Car

by Richard Rowe

Antifreeze is a lot more than just the stuff that keeps your engine block from cracking when temperatures drop. In the earliest days of the automobile, people kept their engines together in the winter by adding some alcohol to the cooling system. Modern antifreezes do the same thing, but they're also complete chemical packages that keep the coolant from boiling as well as freezing, lubricate the water pump and coolant seals, and contain "sacrificial" particles designed to corrode in place of your engine block and cooling system.

Step 1

Park the vehicle on hard, level ground and allow the engine to cool completely. If you're only adding antifreeze, then open the hood and locate either the radiator cap or the coolant overflow bottle under the hood. Turn the cap counterclockwise to open it, and add your manufacturer-recommended antifreeze until the radiator is full, or the coolant overflow bottle is filled to the "COLD" line. If you're draining and refilling the system, do not add antifreeze -- continue to the next step.

Step 2

Kick a pair of wheel chocks in behind your rear wheels, and set the vehicle's parking brake. Lift the front end with a floor jack and secure it on a pair of jack stands. Locate the "petcock valve" on your radiator; it's usually on the bottom corner of one side, facing the engine. Other vehicles may have a valve in the bottom of the radiator facing straight down. It's generally plastic, typically recognizable by the "fin" protruding from it.

Step 3

Place your drain pan under the petcock valve. Grasp the fin firmly and turn the valve either one-quarter or a half-turn counterclockwise to open it, and drain the coolant. Some older vehicles don't have these valves. In these cases, you can only drain the radiator by loosening the lower radiator hose clamp, and carefully sliding the hose off the radiator. This method is quick but very messy, especially when the fluid first begins to gush out; use it only if you have to. Otherwise, wait for the cooling system to completely drain through the petcock, and close the valve tightly afterward.

Step 4

Turn your ignition key to the "On" position, but do not start the engine. Set your heater temperature controls to the maximum settings, and turn the ignition key off. Open the bleed valve on your engine or coolant tube, if so-equipped. Many vehicles now have one or more bleed valves placed at the highest points in the cooling system, which allow air to escape during filling. These valves are typically on or near the thermostat housing, where the upper radiator hose connects to the engine. There may also be on on the upper heater hose, near where it attaches to the firewall. They typically look like a bolt, hex-head screw, or bleed nipple with a hexagonal base. Bolts and hex-head screws typically screw into the top of a second, larger bolt which you must hold still with a wrench while loosening the bleed screw. Nipple-types don't need to be removed completely -- just turn them one or two turns counterclockwise to open them.

Step 5

Slowly add the recommended coolant mix to the radiator or to the radiator overflow bottle if your radiator doesn't have a cap. Pause for 10 seconds periodically while filling the radiator, or just keep the overflow bottle topped up to the "Cold" fill line. Stop when the radiator or coolant bottle will take no more fluid, or when you see coolant start coming out of the bleed valve. When you see coolant coming out of the valve, close the valve by turning it clockwise, and tighten it just snug.

Step 6

Fill your coolant overflow bottle to the "Cold" fill line. If you have a radiator with a cap, leave the cap off for now. Start the engine and allow it to idle up to operating temperature, about halfway up the gauge, or when the thermostat opens and the upper radiator hose gets hot. Add coolant to the radiator through the cap until the level stops dropping, install the cap, and fill the overflow bottle to the "Hot" line.

Step 7

Allow the engine to idle for another 30 seconds, shut it down and monitor the coolant level in the overflow tank. As the engine cools, it will draw coolant in from the bottle to fill any air voids inside. Keep the overflow bottle topped up to the "Cold" line at all times, until the level stops dropping. Start the engine, and allow it to idle back up to operating temperature. Shut it down again, and keep the overflow bottle at the line. Repeat this heating-cooling cycle again, and monitor coolant levels in the overflow bottle for the next 50 miles of driving. Add as necessary, and do not allow the bottle to run dry.

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