Engine Coolant Leaks: Symptoms and Solutions

adding engine coolant
A 50/50 water/coolant blend delivers good protection at both high and low temperatures.

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Coolant leaks are a precursor to a major engine problem, and fixing them should be high-priority. Why? Engine coolant maintains engine operating temperatures in the best range for performance and fuel economy. If the engine is too cold, fuel doesn’t vaporize as easily, leading to poor performance and increased fuel consumption. If the engine is too hot, fuel may combust on compression instead of spark, detonation, which can cause severe engine damage. Excessive heat can also deform the engine, permanently damaging it.

What Is Engine Coolant?

Engine coolant is mostly water and ethylene glycol or propylene glycol, with several additives, such as rust inhibitors, lubricants, and dyes. On its own, water would freeze at 32 °F (0 °C) and boil at 212 °F (100 °C), making it unsuitable as an engine coolant. Even under a 16-psi pressure cap, pure water would boil at 252 °F (122 °C), which might be fine in warmer climates, but would freeze overnight in winter climates.

The addition of glycols extends the liquid temperature range of water, preventing freezing and boiling at extreme temperatures. The typical 50/50 water/coolant blend drops the freezing point to -35 °F (-37 °C) and raises the boiling point to 223 °F (106 °C). A 30/70 blend goes even further, dropping the freezing point to -67 °F (-55 °C) and raising the boiling point to 235 °F (113 °C). Some call it anti-freeze, but that’s just a side-effect of engine coolant’s function. Adding pressure further increases the boiling point, up to 267 °F (130 °C) for a 50/50 blend.

Symptoms of Coolant Leaks

A new engine is usually able to maintain its coolant in the radiator, hoses, and coolant passages. However, damage, wear, corrosion, and other problems can easily cause coolant leaks. If you suspect you may have a coolant leak, look for these symptoms.

Visible Coolant Leak

If you see a puddle on the ground or smell coolant in the car, you've discovered a serious sign of a coolant leak that needs to be repaired before it causes serious damage to your engine. Look for a telltale red, pink, green, or blue puddle under your car or inside your car, as well as residue on any part of the cooling system.

Overheating Engine

When coolant leaks, air will take its place. Because air is compressible, the boiling point will lower, allowing some of the coolant to flash into steam. Air and steam are great insulators and will prevent the cooling system from expelling excess heat. If the temperature gauge is heading toward the red zone or you see a temperature warning light, you may have a coolant leak, even if you can’t see it.

White Smoke

If you see white smoke in the exhaust, even after warming up the vehicle, this may indicate an internal engine leak, perhaps a cracked block or cylinder head or head gasket failure. Under pressure, coolant may be forced into the cylinder, flashing to steam every time the cylinder fires.

Bubbling Radiator

Bubbles in the radiator or in the coolant overflow tank indicate that combustion gases are being forced into the cooling system. This is a sign of a coolant leak, but might also be caused by cracks in the engine, head, or head gasket.

Coolant Leak Solutions

The most obvious coolant leak solution is to find and fix the leak, but finding the leak is not always an easy task. Here are some of the most common ways causes of a coolant leak and how to fix them.

Install a New Radiator Cap

A worn, weak, or leaking radiator cap will not hold pressure, lowering the boiling point and allowing coolant to boil out. It may also allow coolant to leak externally. Luckily, this is a quick and cheap fix. Just wait for the engine to cool, refill the cooling system, and install a new radiator cap.

Replace Cracked Hoses

Over time, rubber radiator hoses and heater hoses may weaken. A burst hose will quickly release all the engine’s coolant, but replacement is usually straightforward. Be sure to use a quality hose, new hose clamps, and clean the sealing surfaces before installation.

Fix a Leaking Water Pump

A leaking water pump is a more difficult replacement, particularly on vehicles that use the timing belt to drive the water pump. The front seal and bearing are susceptible to wear, and replacement may take a few hours. Thus, the standard recommendation is to replace the water pump at the same time as replacing the timing belt.

Repair a Radiator Leak

Because the radiator is exposed, there are a few different ways it can fail, including corrosion, debris damage, and even minor impact. If the coolant leak is caused by a radiator leak, you'll want to repair your radiator.

Fix Internal Engine Damage

If the block is cracked or the cylinder head is warped, your engine needs to be taken to an auto professional for major repairs.

Stop-Leak Products

Stop-leak products are meant for hairline imperfections and minuscule cracks, not the kind of leaks that result in a puddle beneath your vehicle or a coolant smell permeating your car.

The heavy additive and media load in stop-leak can effectively seal tiny imperfections, perhaps even creating a soft “weld” to prevent coolant leaks, but they are not a replacement for necessary repairs. A stop-leak product may save the day as a last-ditch effort, but if you have a coolant leak, a full diagnosis and repair will be required as soon as possible. If you use a stop-leak product, you will also need a coolant flush to remove excess stop-leak.