8 Symptoms of a Blown Head Gasket vs Cracked Engine Block

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.

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.

1) Antifreeze & Oil Mixture

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

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

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

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

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

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

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

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.

16 thoughts on “8 Symptoms of a Blown Head Gasket vs Cracked Engine Block”

  1. Trying to diagnose the engine of a classic car. We assumed it was a blown head gasket, took the heads off and sent them to a shop. The shop just called back saying there were cracks in the head. (We don’t yet know/haven’t had the opportunity to inspect the heads. The shop has been a bit dodgy and we have reason to suspect this may not be true.) If there are indeed cracks in the head, does that mean the block is also cracked? It’s a PRV V6 engine.

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  2. I was told by a mechanic that my truck may have a blown head gasket or a crack in the block cause gas and coolant was mixing to gether. Is that po8

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  3. I have to put antifreeze every few weeks bout4/5 weeks. If i forget about it, it completely empties, then my 15 Chevy Cruze overheats really bad. Once I put more antifreeze, its good until it all happens again. Ive been doing this for about a year now; i keep a bottle of orange antifreeze in my trunk. What does it sound like could be the problem?

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    • It’s possible you have a simple coolant leak. Perform a radiator pressure test to ensure the cooling system holds the amount of pressure it was designed for. While under pressure, check for leaks on the ground and around the engine bay. You may even look in the engine bay and notice it spraying out from somewhere. This happened to me… three times, in fact.

      If you can’t find a leak, this would be a textbook symptom for internal head gasket failure. Internal head gasket failure means the leak stayed within the engine or cooling system, so you probably wouldn’t any coolant on the ground in this case.

      If you do have a failed head gasket, you will likely also see white smoke coming out of the exhaust even after the car has reached operating temperature.

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  4. Have a 2013 v8 5.7L Durango. Performs perfectly and no over heating. But after driving highway speeds once parked will purge coolant out of the reservoir tank. And does not do it on the return trip or driving around town. Temp never goes above 228. No smoke from tail pipe but leak test showed positive for compression gases in coolant. Almost instant positive when doing the test. Could it be a leaky head that hasn’t blown yet? Or something else?

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  5. i have a 85 JD farm tractor with a 3cyl. Yanmar 21 HP diesal. just recently was told i have low compression on 1 cyl. , was within operating range. Since noticed that after just a few minutes of idle or light use that i am seeing coolant dripping from overflow. after inspection i realize that my overflow water is black. obvious that exhaust in leaching into coolant & forcing coolant to back pressure out overflow. is this a sign of cracked head/ block or gasket. does not appear that water is in oil.? also did radiator pressure test and had slow/minimal loss.(not running). if that matters?

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  6. Hi. I have a jetta 5 tdi. In the antifreeze bottle are grey thick stuff floating. The oil cooler has been tested under high pressure and doesn’t leak. The pipes from the antifreeze bottle are clean inside. The oil dipstick are normal. The heat gauge is normal. The car performance is excellent. What can be the cause of the grey thick stuff in the antifreeze bottle? When you put your finger in the inside of the bottle and take it out it looks like oil.

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    • I’m not really sure. It could be some old stop leak in the system, or some other random gunk that has floated to the surface from inside the cooling system. If the cooling system hasn’t been flushed in a while, I would go ahead and flush it to be on the safe side. Otherwise, just scoop out any chunks of the stuff you can reach, then top off the coolant back to the full level. If the car is otherwise performing well I wouldn’t worry about it too much.

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