How to Fix a Blown Headgasket

Disclaimer - this guide is not a substitute for good practices and sound judgment of an experienced and trained automotive mechanic or technician. I certainly recommend that you consult a good shop manual or service manual specific to your vehicle and its drive train before you begin any procedure that invades the interior of a motor. I am not responsible for injury, damage to you or your vehicle, consequential damages of any sort nor loss of effective motor performance or deviation from accepted emissions standards. If you do not understand how to repair a motor it is in your best interest to obtain instruction, training or consult proper manuals and study guides in order to clear up any shortcomings in your knowledge or skills. If you are unable to hew to good advice or to master the practices needed to work on automobiles I urge you to give the job over to someone who does have such skills and who will follow good practices and manufacturer's suggested procedures.

First one must be certain that the head gasket has failed.

Symptoms of a failing head gasket include; unexplained loss of engine coolant, a strange looking film similar to white grease (called Mousse and is similar to the muck that is left by oil tanker spills) which is deposited at points inside of high points of the top of the motor (often the underside of the cap that you remove to fill or add engine oil), small bubbles in the coolant, the scent of coolant in the exhaust and in extreme cases loss of coolant through the exhaust system. In rare cases the flow of coolant out the exhaust port can be quite dramatic.

A definitive test is to shut off the motor, remove the spark plugs and apply a pressure test device to each cylinder through the spark plug port. Loss of head gasket integrity will cause air to enter into the cooling system. Unless the head gasket is ruined in every cylinder there should be some cylinders which do not "bleed down" and others which will bleed down. Such a comparison will guide you to a proper diagnosis. Keep in mind that you must rotate the engine in order to close the exhaust and intake valves at each point in the test! Also keep in mind that damaged piston rings, damaged valves and in rare cases piston damage can also cause some "bleed down" of pressure.

Alternatively the cooling system may be pressure tested and will reveal a characteristic "bleed down" of applied air pressure. Please do mind proper safety rules when opening your engine's cooling system, such as waiting for it to assume a temperature close to ambient. This practice will prevent you from being injured from scaldingly hot coolant.

Procedure to change the head gasket

Caveat - many motors may require some sort of gasket replacement, not just of the head gasket itself but also of intake and exhaust manifold gaskets. There may be other ports and access points in the motor that require their own gasket replacements (such as water ports, emission control devices and so on). In some cases fasteners that attach the head to the motor block may also need replaced. You must to some degree obtain information on your particular vehicle or motor.

In general...

0. Size up the situation. You must remove the head to replace the gasket. Judge which components must be removed to facilitate the removal of the head and see if they interfere with the removal of other components. Determine a good course of action in order to spare yourself needless waste of time, effort and frustration.

A partial list of good practices - as you remove fasteners and parts arrange them on a clean surface where they will not be disturbed. If necessary clean them with an appropriate solvent in order to prepare them for reassembly. This practice will help you to reinstall necessary assemblies in good order and prevent the loss of important fasteners and small parts. If necessary keep a detailed list as you proceed - there is no shame in being careful if it saves you needless trouble.

It is not outside of the realm of possibility that you may have to remove the motor in order to replace the head gasket though I have never needed to do so.

After disconnection of the battery the following order is recommended but is not a substitute for sound practices and good judgment.

1. Disconnect the battery 2. Remove fuel intake manifold and/or exhaust manifold and/or injection system from the head. 3. Remove spark plug wires and spark plugs. 4. If you have an overhead valve motor you must plan to remove or loosen the timing belt or chain in order to remove the head. 5. Remove any valve cover assemblies. You will also probably need to remove any engine emission control components such as exhaust gas recirculation valves. 6. When you have reduced the head assembly to the point that you have a "bare" head, remove the head. 8. Remove the head gasket. Examine the interior of the affected cylinder or cylinders for damage. Also examine the pistons for damage. 9. Examine the heads for damage, such as cracks or checks. Also examine the head for "warpage" as blown head gaskets can be a symptom of an over heated engine. 10. Prepare the surface of the engine block to receive the head gasket. Use a recommended dressing or surface preparation method or solution to insure proper adherence of the gasket to the surface of the head. 11. Replace the head following good practices or manufacturer's suggested procedures for applying torque to the fasteners that attach the head to the engine block. In points where the bolts come into contact with coolant it is recommended that you apply a preservative to insure that the fastener does not corrode inside of the coolant stream. 12. Restore the rest of the parts, following the manufacturer's recommended procedures and practices, including the application of surface treatments, bonding agents and torque specifications.

It is considered good practice to repeat a pressure test on each cylinder after final assembly but before the spark plugs are reinserted. This will insure that possible damage to the motor is detected.

If necessary consult an experienced automotive mechanic or technician, as well as any online or printed resources, before you begin this procedure.

Recommended Tools

1. A torque limiting or measuring wrench is almost always essential for successfully completing this procedure. You may use either a metric or imperial measurement unit but you must insure that you use proper torque values. Consult manufacturer or use good practices (a pattern of tightening the fasteners) in order to insure that the head and other fasteners are re-attached properly. Failure to do so may compromise your repair. If the wrench is old or has seen use or has been previously damage you may wish to consult a reputable firm in order to inspect calibration of the torque wrench.

2. A collection of appropriate tools, not excluding a large socket set, wrenches, screwdrivers, a scraping tool to remove old gaskets, and a good quality straight edge to gage the degree of warpage of the head. Air or electric power tools are useful for disassembly but are not necessarily a substitute for a careful use of hand tools during critical phases such as applying the right amount of torque during reassembly.

3. A good "shop manual" or service manual is an invaluable aid to detail procedures such as replacing head gaskets. Many manuals are available online in pdf format.

I hope that this helps and that any one who uses it will hew to my advice on obtaining proper information before initiating such a task.