How to Test for CO2 in Car Coolant

by Don Bowman

Testing for CO2 in a car radiator is prompted by the suspicion of a head gasket leak. Most of the time, head gaskets develop leaks due to engine overheating. The head bolts are steel while the cylinder head is either cast iron or, most commonly today, aluminum. Being dissimilar metals, when the engine overheats, the head bolts will expand more rapidly than the aluminum, resulting in a warped head. The head gasket, having unequal pressure upon it, will fail at one spot or another. A failure causing a leak can originate from the water jacket to the oil pan, resulting in a tan milkish-looking substance when viewed on the dipstick or under the oil filler cap. Another possibility is oil passing into the water jacket, resulting in oil in the radiator. Another is compression loss to an adjoining cylinder, resulting in a loss of compression in two cylinders and a misfire. Another possibility is a leak from the water jacket into the cylinder, which is the worst-case scenario. Water, unlike fuel and air, is non-compressible and will either break a piston or bend or break a connecting rod very quickly. The last scenario is a compression leak into the water jacket. This is the last check, after all the other scenarios have been eliminated. This test is looking for exhaust gas (CO2) in the radiator, indicating a blown head gasket.

Step 1

Allow the engine to cool if it has just been run. Remove the radiator cap and check the fluid level. For this test, the fluid level in the radiator must be two inches below the radiator filler neck but no lower. This is because, if antifreeze is sucked into the test kit the fluid will be contaminated, resulting in an unreliable test.

Step 2

Open the radiator petcock using the pliers if the fluid is too high, and allow some to drain to bring the level down. If the level is too low, just add water to bring it up to the proper level.

Step 3

Remove the glass cylinder, the suction bulb and the test fluid from the kit. Notice the rubber cone on the bottom of the glass cylinder. This end must be pressed down in the filler neck to seal any escaping gasses. The bulb is used to vacuum gases into the cylinder.

Step 4

Start the engine and allow it to warm up with the radiator cap off. Pour the test fluid into the glass cylinder, to the well-defined test line. Press the rubber cone end of the cylinder into the radiator filler neck. There is no need for excessive pressure, just enough to keep the opening sealed.

Step 5

Place the bulb in the filler hole in the top of the glass cylinder. Make sure the small metal valve on the bulb is up. Squeeze the bulb slowly for one minute, watching the color of the fluid. The color is blue to start with. If the fluid begins to turn yellow or light green there is definitely a head gasket leak. If there is no color change the gasket is good.

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