Causes of Coolant Leaking From the Engine Manifoldby Naomi BoltonUpdated July 12, 2023
Coolant leaks are often the cause when a car's engine overheats. A leak can occur anywhere in the cooling system and is usually easy to find, as the engine coolant can often be seen spraying, seeping, bubbling or dripping from the leaky component in the combustion chamber. The coolant level should be steady to avoid the engine overheating, and a leakage in the coolant system needs to be addressed to avoid causing engine damage or other engine problems. Pay attention to the temperature gauge on your dash or any other causes for concern like white smoke coming from your vehicle or puddles under the vehicle from the tailpipe or the radiator – these can all indicate a bad intake manifold, a blown head gasket, or a vacuum leak that could be causing a lack of coolant.
Intake Manifold Gasket
Several gaskets seal the connection between the intake manifold and the cylinder heads. When these gaskets fail coolant will enter the crankcase or intake port, or drip down the outside of the engine. Intake manifold gaskets on many general engine models are made from plastic, and typically fail between 50,000 and 80,000 miles.
A series of hoses connect the manifold with other engine parts. An old, cracked hose is a common cause of a coolant leak. A cracked and leaky hose must be replaced.
Bad Head Gaskets
The cylinder head gasket connects the engine block with the cylinder head. Coolant can leak into the crankcase and dilute the oil, damaging bearings in your engine. A head gasket leak can also foul the spark plug and cause a lot of white exhaust smoke. Add sealer to the cooling system in an attempt to plug the leak temporarily, but arrange for a gasket replacement in the meantime to fix this intake manifold gasket leak.
Cracked Head or Block
A cracked engine block can cause internal coolant leaks, which will often dilute the oil on the cylinder walls and damage piston and rings. If your car's antifreeze contains silicates, it can also foul the catalytic converter and oxygen sensor. If a lot of coolant leaks into the cylinder, your engine may "hydrolock" and refuse to crank when you try to start it.
Corroded Freeze Plugs
Freeze plugs are often situated just behind the exhaust manifold. Coolant leaks from these plugs may seem like it is coming from the manifold itself. Freeze plugs are the expansion plugs in the side of the engine block and cylinder head, and often corrosion starts from the inside out.
When the engine overheats, the cylinder head can expand, causing damage to the head gasket (a seal between the top and bottom of the engine). This can affect engine combustion and/or cause coolant to mix with engine lubricant. In some cases overheating will crack the cylinder head.
Pistons and Rings
With a bad head gasket, coolant can leak into the cylinders, diluting the oil and eventually damaging the pistons and rings. Coolant in the cylinders can also destroy the oxygen sensor, the catalytic converter and/or cause the engine to go into vapor lock, which will prevent it from starting.
If coolant leaks into the crankcase of the vehicle it will cause damage to the bearings and contamination of the engine's oil, which can affect the oil level as well.
Fluid leaks can occur in the lines carrying automatic transmission fluid through the transmission cooler. This will damage the transmission.
Virtually growing up in a computer repair shop, Naomi Bolton has held a passion for as long as she can remember. After earning a diploma through a four year course in graphic design from Cibap College, Bolton launched her own photography business. Her work has been featured on Blinklist, Gameramble and many others.