What To Do If You Overfill Coolant

It all started so innocently: You’re puttering around the garage on a crisp fall morning — checking for harmful low tire pressure and things like that — when you notice that your car’s coolant tank is low. Well shoot, there’s that partial gallon of premixed stuff you’re pretty sure is compatible with your current ride, so you dump the remainder of the plastic jug in your car’s plastic reservoir. Now, the level is about to overflow the cap will surely turn into an antifreeze equivalent of Mount St. Helens once the engine actually starts to get warm. 

Fortunately, in this case, you can put the proverbial toothpaste back in the tube. For the mechanically inclined, most radiators have a petcock valve on the bottom that you can open — often by hand, without tools — to drain off some of the excess coolant (a mix of antifreeze and water) into a pan or bucket. It won’t immediately appear that the level in the plastic tank is going down. However, the excess coolant inside the tank will eventually be sucked into the radiator to replace the quantity that was drained off, restoring the proper level in the plastic tank. But if you want to cut out the middle man and remove fluid directly from the coolant overflow tank, that’s an option too. 

Along with selling snacks, auto parts stores and hardware stores sell all manner of gadgets to pump or extract fluid, but ain’t nobody got time (or money) for that. Instead, you can requisition your household’s turkey baster to suction the excess coolant from the plastic reservoir. Antifreeze is toxic, though, so be sure to thoroughly clean the baster or, better yet, buy a new one before hosting this year’s Thanksgiving supper. Pro tip: you can buy a new one at your local dollar store. In a pinch, you can also insert a short length of tubing, then hold your thumb on top as a makeshift pipette.

However, you opt to alleviate your vehicle of your coolant overfilling mistake, do use caution storing or discarding the removed fluid. As previously mentioned, antifreeze is toxic and pets have been known to become gravely ill after lapping it up, so make sure that doesn’t happen. Either recycle the liquid or store it in a secure container. If any coolant spills on the ground, be sure to promptly wipe it up. 

To avoid adding too much coolant to your vehicle going forward, pay attention to the markings that are present on the side of the coolant tank. Also note that some overflow reservoirs have a dipstick instead. It’s okay to check and add coolant to a warm engine, but you’ll want to avoid removing the reservoir’s cap when the engine is scalding hot. Otherwise, burning hot fluid and vapor can escape.

At a minimum, the coolant tank should have “full” and “low” fluid level indicators imprinted on the side. Sometimes, these indicators are also be labeled “hot” and “cold” instead of or in addition to full and low. Ideally, the coolant level should be between the high and low marks on the coolant tank or dipstick. If you’re perpetually having to top off the coolant reservoir, that could indicate a larger problem, such as a leak in the cooling system or white smoke that could signal a faulty head gasket.

Finally, not all coolant is created equal. Some coolant is ready-to-go straight from the container. However, you can also purchase pure antifreeze that needs to be mixed with distilled water in a proper ratio, so do pay attention. Some engines also require a very specific type of coolant, which is sometime identified by its color.