Signs of a Coolant Leak (& What You Should Do)

Common Causes & Fixes for Coolant Leaks

Leaky radiator caps Radiators are pressurized, so when a cap is loose, it can cause the coolant to escape. Caps are prone to deterioration over time, and even their springs may start to wear out. Symptoms: One of the first signs of a leaky cap is a coolant leak. However, left unaddressed, a leaky cap can cause a radiator hose to collapse, the engine to overheat, and even boil over. Automotive Repair Specialist Duston Maynes recommends promptly bringing your vehicle to the shop if there’s a radiator leak. It can be the beginning of something more severe. The Fix: Allow the vehicle to cool down before locating the radiator cap on top of the radiator. Unscrew the cap with your hand. Look for signs of damage, cracks, or corrosion. Purchase a matching radiator cap and screw it on. Cost of Repair: A cap replacement can range between $13 to $40.

Damaged radiator or hoses A radiator is one of the key components of an engine’s cooling system. It dispenses a mix of antifreeze (coolant) and water throughout its tube, which releases the engine’s heat. If there are visible cracks, holes, or corrosion on the radiator, this can affect its ability to keep the engine cool. Symptoms: If there’s a hole or crack on the radiator, look for signs of antifreeze leak. Look beneath your car for any colorful puddles. Antifreeze can look green, blue, pink, orange, or yellow. Similarly, pay attention to your check engine and engine temperature gauge—if it’s red, this is a sure sign your car is overheating. The Fix: If you can locate a crack in your radiator, apply an epoxy-resein resealer directly to the crack or hole. This should only be a temporary measure, according to Maynes. Relying on a sealant can cause a clog in the process, and it’s best to refer to a professional. Cost of Repair: A leaking radiator can range between $700 and $1,000, depending on the repair, vehicle make and model, and the radiator type.

Failed water pump Water pumps circulate the coolant through the engine. Without it, the engine can overheat. Water pumps should be replaced every 60,000 miles in most cars to ensure the engine is effectively cooled. Symptoms: A bad water pump will cause coolant to leak, leading to an overheating engine. You may also hear a high-pitched squealing or whining noise from the friction of hot components rubbing against each other. The Fix: Locate the water pump beneath the lower part of the engine, near the drive belts. Look for signs of cracks, holes, or corrosion. To fix a water pump, detach the negative battery line before removing the radiator cap and emptying the radiator of its liquids. Detach the radiator hoses, belts, and fan shroud using a wrench. Apply an industrial cleaning solution to the pump and apply a gasket sealant before replacing the water pump. Cost of Repair: A repair or water pump replacement can range from $400 to $1,000.

Defective reservoir or expansion tank A vehicle’s reservoir or expansion tank is a component that holds excess coolant and minimizes excess pressure in the engine coolant system. A crack or hole in the tank can cause coolant to leak, and if left unaddressed, your engine will overheat and eventually break down. Symptoms: Look for signs of a coolant leak beneath the vehicle. Coolant is colorful, so look for blue, green, yellow, orange, or pink spots on the ground. Inspect the temperature gauge to see if the vehicle is starting to overheat. The gauge will tick closer to “Hot” if it is. The Fix: For small cracks and holes, apply a bead of an epoxy resin or a sealant. Follow the manufacturer’s instructions on the product. For large cracks, it’s best to replace the reservoir entirely. Cost of Repair: A replacement can run between $442 and $467.

Overheating engine As mentioned earlier, a persistently hot engine is often a result of a coolant leak. When the coolant levels drop too low, the engine cannot effectively cool down quickly, leading to overheating. Left unaddressed, it can cause serious damage and engine failure—putting yourself and other drivers at risk. Symptoms: On your vehicle’s dashboard, pay attention to the temperature gauge. In most vehicles, it will be a small gauge with C for “Cold” and H for “Hot.” Over time, the engine may release heavy steam and a sweet, burnt smell. The Fix: Immediately turn your vehicle off in a safe location and avoid driving. Inspect the coolant levels under the vehicle's hood. On the side of the coolant reservoir, check that the coolant is between the “low” and “full” marks. Add more coolant to see if this helps. If not, seek the assistance of a professional to diagnose the problem. Cost of Repair: Engine-related issues can run anywhere from $100 to $8,000 depending on the issue and vehicle make and model.

Blown head gasket Similar to radiator caps, head gaskets are seals between the engine block and cylinder heads. They keep the combustion chambers sealed, which allows the vehicle to spark and start. The gaskets help keep oil and coolant from mixing, but when there’s a leak, it can prevent your car from starting correctly. Symptoms: A significant loss in coolant is a key sign of a bad head gasket, especially if you can’t find any leaks. Similarly, you may hear a knocking sound when starting your vehicle and see white smoke coming out of the tailpipe. The Fix: Purchase replacement head gaskets and remove the old ones. To replace the gasket, clean the surface to remove any rust or debris in contact with the new heads. Carefully position the new head gasket and press down to fit it in. Install new bolts so you have a snug fit. Cost of Repair: A blown head gasket replacement can run between $1,000 to $2,000, depending on the complexity of the engine.

How to Find a Coolant Leak

Inspect the bottom of your radiator to identify a leak. You'll need to locate the leak first to determine how bad a coolant leak is. Inspect the bottom of the radiator and check the radiator itself, the hose, the drain valve, and the reservoir. Look for a slow drip from one of these places. Additionally, you can park your vehicle on top of cardboard and wait for the leak to drip. Anything that can’t be resolved with an epoxy resin or similar sealant should be inspected by an experienced mechanic.

Is it safe to drive with a leak?

No—avoid driving until you can have your vehicle inspected. If you suspect your vehicle is leaking coolant, locate the leak first to determine its severity. If it’s a slow leak, drive to your local mechanic for an inspection. However, if it leaks too much, Maynes recommends towing your vehicle to avoid overheating the engine.

Preventative Maintenance

Drain, refill, or flush the coolant as the manufacturer recommends. At some point, you’ll need to change your coolant. On average, most people opt for a simple refill. But, for older vehicles, the coolant should be drained or flushed every 2 to 3 years, or around 60,000 miles. Coolant can last up to 5 years, or 100,000 miles for modern vehicles. Refer to your vehicle’s owner manual for the manufacturer’s recommendation for coolant changes. Change your coolant when you notice a change in the color or constancy of the cool, a sweet, strong smell from the engine compartment, or if the engine temperature increases.

Inspect coolant levels every 3 to 6 months. To keep your vehicle in tip-top shape, look to the coolant levels every 3 to 6 months to see if it needs to be topped off or drained. Look at the overflow tank next to the radiator and ensure it reaches the fill line outside the reservoir. If it’s beneath the low line, use a funnel to add more coolant in. Coolant should be flushed when it’s brownish or colorless. Healthy coolant will be green, blue, yellow, or red.