How To Diagnose Cracked Cylinder Heads

Diagnosing a cracked cylinder head can be diagnosed in three ways.  I will try to explain the diagnosis steps in easy terms, so that you can identify the warning signs and save the remainder of your car’s engine from further harm.

First, what exactly are cylinder heads? 

Cylinder heads are the detachable portion of the engine, which are usually fastened to the top of the cylinder block, and contains all or most of the combustion chambers.  On overhead valve engines (OHV), like with this ’99 Mercury Sable Wagon, the cylinder heads contain the valves and their operating parts.  On overhead cam engines, it contains the camshaft as well.

A Cylinder block is the main structural member of an engine where the cylinder heads are found, crankshaft and other principle parts. 

The cylinder heads contain all of the moving parts of the fuel and exhaust valves, springs, and push rods that operate the fluctuation of fuel and exhaust throughout your car.  When the heads develop a crack due to wear and tear in your engine, it allows the oil to mix with the cooling system of your engine.   

What Causes Overheating?

There could be a few reasons causing the car to overheat.

1. 1.    Insufficient coolant in the system
   2.    Drive belt defective or not adjusted properly
   3.    Radiator core blocked or the radiator grill may be dirty and restricted.
   4.    Faulty thermostat.
   5.    Cooling fan not functioning properly
   6.    Radiator cap not maintaining proper pressure.  Either pressure test the cap yourself, or have a repair shop do it for you.
   7.    Defective water pump
   8.    Improper grade of engine oil.
   9.    Inaccurate temperature gauge
   
   
   If your vehicle is experiencing unexplained coolant loss, as in you see no visible leaks, there may be a few causes…
   
   
   
   

1.    Overfilling the system

2.    Coolant boiling away due to overheating

3.    Internal or external leakage.

4.    Faulty radiator cap

5.    Cooling system being pressurized by engine compression.  This could be due to a cracked head or block, or by leaking head gaskets.  Have the system tested at a repair shop for combustion gas in the coolant.

External coolant leakage

1. Check for deteriorated or damaged hoses.  Loose clamps at hose connections
2.  Water pump seals defective.  In this case, water can be seen dripping from the weep hole in the water pump body.
3.  Leakage from radiator core or expansion tank. This will require the radiator to be professionally repaired.
4.  Leakage from the coolant reservoir or expansion tank.
5. Engine drain plugs or water jacket core plugs leaking.
6.  Leak from coolant temperature switch.
7. Leak from damaged gaskets or small cracks.

Internal leakage

Internal coolant leaks can often be detected by examining the oil.  Check the dipstick and inside the rocker arm cover (valve cover), for water deposits and an oil consistency much like a milkshake.  Some of the causes may be due to…

1.   .  Leaking cylinder head gasket.  Have the system pressure tested or remove the cylinder head and inspect.
2.      .    Cracked cylinder bore or cylinder head.  Dismantle the engine and inspect.

3.    Loose cylinder head bolts.

How to Diagnose a Cracked Cylinder Head:

1.    Remove your radiator cap and start the engine. Wait for the engine to warm up enough for the thermostat to open. The circulation of water will tell you if oil is in the water by simply dipping your finger into the fluid.

2.    Remove your oil stick from the engine block. Closely inspect the dip stick for beaded water droplets on the surface.

3.    Visualize the flow of the water being circulated through the engine as it runs. If you see bubbles floating in the coolant it could mean that a crack has formed within the engine block. It will also make the engine run hot, so do not run the engine for a long period of time.

These three things can help you identify a cracked cylinder head on your car, but it is always best to take your car to a licensed professional to have your engine coolant tested for adequate pressures. 

Your car's performance will tell you when a cracked head appears out of nowhere. The car will idle sluggishly and the engine will run hotter than a normal temperature during operation. The engine could also stall due to protective modules placed throughout your cars system to prevent damage to the motor.

It is a good rule of thumb to have your car placed on a diagnostic machine that goes through your cars computer to identify problems that may have caused the crack to form. The repairs to cracked heads can be a costly problem, but if you identify the problem ahead of time, other problems can be prevented. Cracked heads can cause Valve guide wear, Piston rings to seat (Thus the loss of compression to engine), and the engine to run hot and possibly seize the engines cylinders. The mix of water and oil inside the engine block can cause the rod and rod caps to break and blow through your oil pan beneath the engine in some cases. The main culprit to cracked cylinder heads is poor cooling from your cars system. Improper fluid levels let the engine heat up and then cracks appear.

In this ’99 Mercury Sable Wagon, the car had been overheating, and upon visual inspection of the water pump, I could see that there had been leaking from the weep hole.  I replaced the water pump and the thermostat.  When the old water pump had been taken off, I could see the significant amount of rust damage to the pump.

Signs of a Cracked Cylinder Head

1.    Unexplained loss of antifreeze.

2.    White smoke from the tailpipe.

3.    Sudden overheating.

Always keep coolant or antifreeze in your car, not water.  When replacing the water pump (if that is the cause of overheating), always replace the thermostat as well.  If your system contains a lot of rust, flush out the system thoroughly and replace with antifreeze.

If your cylinder heads are indeed cracked, keep up-to-date with this blog, as I will have videos up showing the disassemble procedure, and explain why some of the components are removed, as I have noticed not everyone removes these particular items.  There are plenty of videos on the way.

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