Diagnosing and Replacing a Faulty Head Gasket: The Ultimate Guide

The head gasket on your car is nothing but a piece of metal coated with a rubber-like material, but despite this, a head gasket malfunction is one of the most crippling ailments an engine can face. To understand why this is a big concern, you need to understand the important role your head gasket plays in your engine’s health. Furthermore, the automotive industry as a whole is facing a skills shortage, so this knowledge could be invaluable. It’s also a lot cheaper to do it yourself… 

Infographic | How to replace an automotive head gasket
Thanks to digitalmicrometers.co.uk for the graphic!

But first, what is a head gasket?

Replacing a Faulty Head Gasket

The seal situated between the engine block and cylinder head assembly is what the cylinder head gasket is. An in-line engine design consists of one cylinder head, these are arranged in a straight line along the engine block. A “V” shaped engine design like the V6 or V8 will consist of two cylinder heads, one for each bank. A V6 engine has 3 cylinders located on each bank.

Note: A substantial amount of labor is included with the repair of the cylinder head gasket even if the displacement engine is smaller in size. This is not a job for beginner auto mechanics!

Get a professional to determine whether cylinder head gasket repair is required or not with the assistance of official testing. This repair is intensive in nature and cannot be simply done for any reason at all. At times, it can end up doing much more harm than good if not done properly.
The correct bank must be serviced on a “V” design if repair for both is not being done simultaneously.

Word of Caution

Ensure that you always practice safety while working on your car to prevent any injury. Put on the recommended safety gear including gloves and safety glasses while handling engine oil, coolant and other components of the vehicle.

Explained below is the A-Z guide that will be your gospel to diagnose and replace the faulty head gasket of your vehicle.

Part 1 – Collect Information and Supplies

Replacement parts required:

Tools required:

Worth mentioning that online repair manuals are a lot cheaper than paper versions. We personally use Chiltondiy.com and/or Alldatadiy.com. I think they are the biggest names in the game but I could be wrong so feel free to use whatever service provider you like.

Must-have Tools for Auto Mechanics

See Also: Must-Have Specialty Tools For Auto Mechanics

Step 1 of Part 1 – Locate the VIN

Find vehicle information which is specific and relevant to your vehicle. This is to make your search for car parts much easier.

Replacing a Faulty Head Gasket

Your vehicle is furnished with two very crucial stickers. The emissions sticker under the hood will inform you about the size of the engine. The label inside the driver’s door jamb will display the vehicle identification number or VIN.

Step 2 of Part 1 – Find a vehicle service manual for your car

The vendor of the car parts will usually enquire about the vehicle year, make and model to locate the suitable spare parts for your car.

Note: The size of the engine really matters as several engine designs vary and the components differ from one another, as this article explains.

Tip: A vehicle service manual is generally more detailed than the vehicle owner’s manual. The service manual will consist of crucial information and will also include some repair procedures.

You will be able to easily find this at many auto parts stores and online vendors. If you do not find a service manual for your vehicle on the shelf, request an associate about ordering one. They are fairly cheap and the information it contains is invaluable.

The service manual will enlist the special tools that will be required for repairs and will state which components to eliminate during the repair process. It may be necessary to monitor the procedures a couple of times before commencing. Get acquainted with the work you are going to perform before starting to work on your car’s engine.

Tip: When looking for a cylinder head gasket, try buying a complete one that contains many different seals. Even if these kits contain seals that you might not necessarily need or has duplicates, it is better to have an important seal when you really need one instead of not having any.

When any component is removed, any related seals will have to be switched so as to eliminate the potential of leaks when the engine is reassembled. After the seals are replaced, it is essential that you employ the fasteners for each component at the required torque specifications.

Part 2 – Dismantle the Engine

Step 1 of Part 2 – Detach the battery

As it is simple to activate the starter assembly on some vehicles by accident, it is essential that you detach the battery when performing any chief repairs on your car.

Note: Always disengage the negative or black cable on the battery first.

Word of Caution

Loose wire connections carry the risk of short circuits and can end up damaging very sensitive and expensive equipment or emanate sparks that may cause fires. This is hazardous, so be sure to disconnect the battery before doing anything else.

Step 2 of Part 2 – Drain engine oil and engine coolant

Ensure that you drain the engine oil from the engine oil drain port. Place the drip pan below the engine to hold the old oil and open the oil drain plug. This way, if engine coolant spills atop the crankcase, it will flow out instead of settling in the engine.

Note: Do not forget to dispose of the old engine oil in the oil pan so that you do not end up adding new oil on top of it or you will have to fix the entire engine assembly.

Drain the coolant from the radiator drain port or by removing or loosening the lower radiator hose. Be sure to take out the radiator cap.

Tip: In some instances, the lower intake manifold or the cylinder head will have a coolant drain port of its own.

Step 3 of Part 2 – Take out all components from the cylinder head
Replacing a Faulty Head Gasket

All components attached to the cylinder head must be removed. Many nuts, bolts clamps, sleeves, and fittings are involved in this step and you may lose track of things. Try taking pictures or write down a description of each part to help you remember where everything goes once all aspects are ready to reassemble the engine.

Bag and label everything. It will be a good idea for you to keep some parts and their respective fasteners in the same bag. One component may have fasteners that are of different lengths. Mark these as these would go back precisely where they came from to keep away from any kind of engine damage.

Some bolts involved in the teardown are known as “torque to yield”. These are generally stretched upon installation and will require replacing once they are removed. Keep a watch on these bolts and do not forget to replace them with new ones.

Word of Caution

If reused, the ‘torque to yield’ fasteners have a pretty good chance of breaking off into the engine block or cylinder head. The broken pieces will have to be fished out and if the hole is damaged, it needs to be fixed.

Step 4 of Part 2 – Take out the fasteners in sequence

Several components such as the cylinder head, intake, valve cover, and exhaust manifolds require the removal of the fasteners in a certain sequence to shun warping or cracking. This information is usually detailed in the vehicle service manual.

Some vehicles are endowed with overhead camshafts which may be either dual overhead camshaft (DOHC) or single overhead camshafts (SOHC). This basically means that the camshafts are situated in the cylinder head. On these types of engines, the crankshaft and camshaft may be linked by a timing belt or chain.

Note: The timing belt or timing chain assembly requires the following of a certain procedure for removal in order to safeguard the internal components of the engine. Pay heed to the procedures and timing marks as these markings are vital to the operation of the engine. The assembly might suffer from significant damage if mistakes are made.

Some vehicles may have a unique engine design referred to as the overhead valve (OHV). Many OHV engine designs have the camshaft housed inside the engine block and make use of lifters, pushrods, and rocker arms to trigger the valves in the cylinder head.

Typically, the engine timing components were excluded from the removal of the cylinder head, but if these components are eliminated, they have to be installed in exactly the same order.

Note: Different types of engine designs make use of different lengths of pushrods for the intake and exhaust valves. If these components are jumbled, engine damage is quite possible.

Replacing a Faulty Head Gasket

Many timing belt kits come with a marked belt for easy installation. The markings on the belt vary for each type of timing belt kit and will be in perfect alignment with the markings on the engine components.

The cylinder head gasket or seal lies under the cylinder head assembly. The material used for the same can range from metal to a material that will crush after the installation of cylinder head bolts and torque. Every now and then, both materials are used in the construction of the cylinder head gasket.

This gasket must resist combustion pressures and temperatures. Often, you may look for breaks between two cylinders or a break where an oil or coolant port seal has cracked.

Part 3 – Scrutinise the Cylinder Head Assembly

The engine block and cylinder head assembly consist of ports through which the engine oil flows and provides the necessary lubrication. Also, the engine coolant flows to control the temperature.

The cylinder head gasket is cut in a way that it seals each cylinder as well as the respective oil ports and coolants so the fluids do not end up mixing and the compression from one cylinder does not seep into another.

Tip: In many cases, a malfunctioning cylinder head gasket will let oil into the cooling system and cause the coolant to turn into brown sludge. You may take note of the sludge while pulling the radiator cap off or inside the engine when you take out the oil filler cap.

Step 1 of Part 3 – Examine the engine block and cylinder head

The mating surfaces of the engine block and cylinder head must be examined thoroughly for flatness and uniformity in order to ensure a perfect seal.

In order to get a professional cleaning and inspection, send the cylinder head assembly to a machine shop. In many cases, a valve replacement will be required. Enquire with the technicians at the machine shop for instructions on what to bring and for details on their services.

Tip: You can buy a machined straight edge to gauge the flatness of the engine block and cylinder head mating surfaces. The vehicle service manual will consist of specifications on the measurement limit.

If the engine block or cylinder head mating surface is not perfectly flat and straight all over, it is a sign that the component has to be replaced. The technicians at the machine shop will examine the flatness of the cylinder heads, but you will be in charge of keeping tabs on the engine block.

Place the straight edge across the engine block deck. Switch on the flashlight and shine it onto one side. Confirm if you can see light peeking through between the engine block and straight edge tool. If you can, then the engine block is in dire need of thorough servicing. If the deck is not uniform and flat, the light will peek from between the spots that have warped.

Step 2 of Part 3 – Clear out the engine block and cylinder head assembly

The mating surfaces of the engine block and cylinder head assembly must be squeaky clean. When you ship the cylinder head to the machine shop, the mechanics will look after its cleaning and servicing.

Note: If you take it upon yourself to clean these components yourself, do not forget to check the intake and exhaust manifold mating surfaces. Be warned that any problems that may have ruptured the cylinder head gaskets might have harmed the cylinder heads as well and to fix this, special tools and procedures may be required.

Word of Caution

DO NOT make use of a revolving disc or grinding wheel to clean the surfaces as these tools can end up taking out too much metal if not used properly. These tools generate many small particles of metals and may deposit them in places that are hard to reach within the engine block. If dirt and debris were to fall into the combustion chamber around the pistons, it may result in scratches along the cylinder walls.

Step 3 of Part 3 – Examine the other components taken out during disassembly

There cannot be a better time than now to examine the other components for damage or wear and restore them to prevent any kind of trouble in the long run.

Note: Change the spark plugs, oil, coolant, belts, engine coolant thermostat, ignition wire, timing components, worn pulleys and any seal that was ruptured during the removal process. The engine component and tools that you may require for the procedure may vary depending on the application.

Step 4 of Part 3 – Clean the threads

At times rust and dirt can collect and build upon the threads or spiral grooves of the fasteners and within the bolt holes. There is a possibility of the fasteners getting stuck on the dirt resulting in inaccurate torque numbers. You can go to your nearest local hardware store with your cylinder head bolts to find the correct bolt size and thread pitch. With this

With this measurement, you can buy a tap of similar measurements. Use the tap on the cylinder head bolt holes to clean any dirt that has collected along the threads.

Tip: A number of engine blocks have studs that are installed in the block. A cap nut is fitted after fixing the cylinder head on the studs. Take reference from the manufacturer’s recommendations for handling these studs. The studs may need to be changed and replaced and the stud holes will have to be cleaned thoroughly.

Part 4 – Reassembly

Step 1 of Part 4 – Spray the cylinder head gasket with a sealer

If appropriate, spray both sides of the cylinder head gasket with the sealer prior to laying it atop the clean engine block. Or else, lay the bare gasket upon the clean engine block.

Tip: Several vendors sell a copper sealant spray to help make sure that the seal applied is sturdy when a new cylinder head gasket is installed.

Tip: If studs are made use of to hold the cylinder head down, install the studs before you can fit the gasket. Designs sans studs are often furnished with alignment dowels to keep gasket immobile while placing the cylinder head on top of it.

Step 2 of Part 4 – Install the cylinder head

Once you are done cleaning the surfaces and sitting the gasket in place. Install the cylinder head and fasten it down.

Tip: The service manual will contain information regarding the fastener torque and proper tightening sequence. Similar to when taking out the components there is a specific pattern to follow while the reassembling is being done so as to make sure that the sealing process is done with absolute accuracy which in turn will guarantee the least stress on the components to be fixed. In major cases, several passes of increasing torque measurements will be needed. Stick to following the procedure and use a calibrated torque wrench.

Step 3 of Part 4 – Replace all the components that were earlier removed

Retrace your steps and install all the components that were taken out earlier from the cylinder head assembly.

Tip: Check with your notes and pictures to not lose track and keep in mind to take a good look at the components, fasteners, and the mating surfaces.

Note: Be sure to clean all the mating surfaces, the threads on the grimy bolts and bolt holes and replace any seal that was disrupted in the process of dismantling. Some components might not require a seal, but do require a silicone paste or gasket maker which can easily be found at your local auto-parts store.

Mechanical Timing (if applicable): The mechanical timing assembly is utilized to tie the crankshaft and the camshafts of the engine together. As the crankshaft starts to spin, the piston moves up and down in the combustion chamber. The camshaft(s) set in motion the valve train to open and close the valves at just the right moment. If the mechanical timing is incorrect, the pistons may contact the valves and end up causing serious damage.

With OHV (overhead valve) applications, you may not be required to meddle with the timing components. With an OHC (overhead camshaft, single or multiple) application, the timing components have to be dismantled to take out the cylinder head. Follow the directions listed in the service manual for the accurate assembling of all the parts.

Step 4 of Part 4 – Connect the battery and refill the fluids

Reassess all the work you have done so far before you connect the battery. Fix the positive cable first and then the negative one.

Word of Caution

If you install the cables in the reverse order, it may cause sparks to fly which has the potential to ignite any flammable liquid present nearby.

Once you are comfortable with the assembly, refill the engine with oil. Check the oil level in the engine and do not forget to use a new filter.

Replacing a Faulty Head Gasket

Also, fill the radiator with coolant until you have reached the max level and wait. You are likely to see some bubbling. This could be because air may get trapped in the cooling system. The cooling system has to be bled before starting the engine. In some cases, it helps to lift the front section of the vehicle so that air can travel to the highest point in the system or the overflow tank. Keep a check on your coolant levels and make sure that they are sufficient.

Step 5 of Part 4 – Check for faults

Get in your vehicle and turn the ignition key to the ACC or ON position. Refrain from starting the vehicle just yet.

At this point, you are free to attach the code reader that is, if you have one.

In major cases, a code will be fixed instantly if a component has not been plugged in. If in case any codes do pop up, it will become easier to trace the component you may have left unplugged.

Step 6 of Part 4 – Set the climate control

Start the vehicle and crank the climate control to the maximum level of heat. This will let the coolant to enter the heater core, giving it the best chance to remove any stubborn air bubbles from the cooling system.

Tip: Refrain from racing the engine. Just let it sit idle and match up to the temperature slowly.

At regular intervals, check the readings on the instrument cluster and step to the engine bay to look for any leaks or smoke. At times, the new seals, especially the head gaskets and exhaust manifold seals may emit steam or smoke.


You have successfully replaced your engine cylinder head gasket on your own!

If you have any queries or find yourself stuck while installing the cylinder head gasket, seek expert advice. It is recommended to consult a certified mechanic if you notice a lot of steam and smoke emitting from the engine after you are done replacing the cylinder head gasket.

If you hear squeaks emanating from the timing belt or if you feel that it needs replacing, get a mechanic to come and inspect or replace the timing belt.

Replacing a Faulty Head Gasket

Anna Barton is a problem solver, coffee trailblazer, passionate creator, and an Automotive aficionado.