8 Symptoms of a Blown Head Gasket vs Cracked Engine Block

(Updated on July 9, 2020)

The two main parts of any engine are its cylinder head and engine block. The block contains the pistons and cylinders, while the cylinder head contains the rocker arms and valves.

In between the block and cylinder head is the cylinder head gasket. This gasket serves as a seal for all the cylinders inside the block. The seal prevents coolant from leaking out of the cylinders and it also prevents oil from leaking into the cylinders and mixing with the coolant.

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Most importantly, if there is ever a problem with the engine block or the cylinder head, the gasket will allow the mechanic to separate these two big pieces of the engine so that they can be individually repaired.

If you suspect you have a blown head gasket, it may actually be a cracked engine block, and vice versa. The symptoms of each can be similar.

3 Symptoms of a Blown Cylinder Head Gasket 

A cylinder head gasket is bound to blow out after a while. This could cause the motor oil, fuel, and/or coolant to mix with each other in the internal combustion chamber.

Since the head gasket is meant to prevent the mixture of these fluids, a blown head gasket could cause this and the results can be catastrophic. Below are three of the most common signs that indicate you have a blown head gasket.

Related: The Dreaded Subaru Head Gasket Issue

1) Antifreeze & Oil Mixture

coolant in oil

A blown cylinder head gasket can cause oil to mix with the antifreeze fluid. But the same can happen with a cracked engine block so another symptom must also be present.

2) Engine Overheating

engine overheating symptoms

If the coolant is leaked into the oil, then it won’t be able to do its job properly of cooling down the engine’s components. This will cause the engine to overheat. The smart thing to do if your car is overheating, is to simply pull off to the side of the road and not continue driving.

3) Poor Engine Performance

car hesitates when accelerating - gas pedal

Once you have an overheated engine, it’s performance will diminish greatly. The biggest issue will be slow acceleration and engine stalling since you then likely have low engine compression as a result.

5 Symptoms of a Cracked Engine Block

The engine block is what houses and protects the cylinders of your engine. The case of the engine block is lubricated to prevent any overheating of the cylinders or components inside of it.

The top of the engine block is where the cylinder heads are located. It closes the cylinders from the topside and allows the combustion chamber to be formed. It’s fairly rare for the engine block to ever get cracked, but it has happened before.

Once it does, the engine will begin to have all kinds of problems and present some very bad symptoms. After all, if the engine block can no longer protect the internal components from excessive heat and cold, then the entire engine is literally toast.

Here are five common signs you can expect from a cracked engine block.

1) Oil & Antifreeze Mixture

coolant in oil

Engine oil and antifreeze fluid can mix together if there is a serious crack in the engine block. The antifreeze fluid will be able to find its way through the crack and then circulate with the oil. This will spell major trouble for the engine.

As noted above, oil mixing with antifreeze can also indicate a blown head gasket so consider other symptoms as well.

2) Engine Smoke

smoke from engine

A huge symptom of a cracked block is smoke coming out of the engine. If you let this go for too long, it will lead to other engine problems.

The smoke is due to emissions fumes leaking through the crack instead of the exhaust system and out the tailpipe. With this you will also likely experience a drastic loss of power when trying to accelerate.

3) Seeing a Crack in the Block

cracked engine block

If you truly need to confirm that you have a crack in the engine block, then just perform a visual inspection of the block to see if it has a crack in it. Of course, it usually isn’t as simple as popping the hood open.

If you don’t have the mechanical experience, you can hire a mechanic to do this for you and to get a certain diagnosis.

4) Engine Overheating

engine overheating symptoms

The casing of the engine block helps keep the engine’s components cool and lubricated. If there is a crack in the block, the engine won’t have the proper cooling available which will lead to the engine overheating and eventually internal damage if driving continues.

5) Low Compression

low compression causes

The internal combustion process allows engine compression to take place. Since the combustion takes place in the engine block, any crack that forms on the block will result in reduced compression since air is escaping. Once that happens, the performance of the engine will diminish.

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