Head gasket replacement is a labor-intensive but necessary process when a vehicle’s head gasket fails. While there are some alternatives to temporarily repair a leaking head gasket, people who choose this route often face even more expensive repairs to other components from damage caused by using that type of product along with having to replace the failed head gasket that started the whole issue. The cost to replace a head gasket can multiply quickly if a cheap sealant job fails and causes damages to your engine block, engine bearings, cylinder head, radiator and more.
What does a head gasket do? Your car’s engine is divided into two main parts, the cylinder block where the pistons, connecting rods and crankshaft reside and the cylinder head where the valves, spark plugs and camshaft(s) are located. Cushioned between these two engine parts is the head gasket. This gasket can be multi layered metal or graphite composite in design. The head gasket’s job is multi-fold: to seal combustion chamber pressure that can reach in excess of 2000 pounds per square inch with extreme temperatures of nearly 3,000 degrees Fahrenheit during the power stork over 50 times a second and highway speeds. It also has to separate coolant passages that hold almost 20 pounds per square inch of pressure (with temperatures over 230 degrees) and engine oil passages that typically run 40-70 pounds per square inch. All this sealing must be achieved and maintained while withstanding the stress of the two surfaces expanding, shrinking and warping to a point.
The job of a head gasket requires it to be under a severe amount of heat and pressure. The stresses of everyday driving can eventually take its toll on this gasket. While head gasket failure is not an extremely common issue, failures of this type do occur often enough to place increased importance upon recognizing the symptoms of such a condition. Head gasket failures are usually the result of cooling system issues (engine overheating) but not always. Some head gaskets are more prone to failure due to design flaws in the gasket design or surface finish of the sealing surfaces. (Subaru, GM, BMW and Toyota are infamous for gasket design flaws on some applications)
The most common head gasket failure: coolant improperly enters the combustionchamber. When the piston is on its down stroke it pulls in air and fuel in preparation for thecombustion process. With a compromised head gasket, coolant also enters the system. Then when the piston comes back up to Top Dead Center (TDC), the fuel ignites from the spark. But so does the misplaced coolant. This is what causes excessive white smoke to come from the tail pipe. When there’s an excess, the vehicle runs rough. When you have too much coolant, the engine will stop in its tracks as the result of hydro-lock. This sudden stoppage could bend a connecting rod, causing internal engine damage.
Another possibility is when the piston comes to TDC before ignition point, it pushes 200 lbs of pressure into the cooling system causing air to displace the liquid coolant in the cooling system. Air pockets trapped in the cooling system can cause rapid hot spots/overheating of the cylinder head resulting in excessive expanding/warping of the gasket sealing surface. This causes a higher percent of the gasket surface to fail and leak making the problem worse, especially with all aluminum engine block and cylinder head vehicles.
With a failed head gasket pressurized oil can run into the coolant system and vice versa. The mixing of the two creates a "chocolate milkshake"-looking effect. This is not good. The coolant in the oil system reduces the lubricating properties of the engine oil and will ruin internal components of the engine, sometimes immediately. Left unaddressed, the cost to repair or replace this kind of engine damage goes well beyond a head gasket replacement.
Early Warning Signs Early warning signs that your vehicle needs head gasket repair include:
The answer depends on lots of variables, the type of engine and how the gasket fails. Generally is advised to not drive the vehicle if you believe your head gasket has failed. You could cause significant damage that could quickly turn a head gasket replacement into an engine replacement.
The Cost of Head Gasket Repair The price of head gasket replacement or repair can vary between different mechanic shops for many reasons. Each head gasket replacement is a little bit different. Nobody can tell you exactly what your car will need until the engine has been disassembled and inspected. That said, anybody who has done a few will have a pretty good idea what the vehicle is likely to need. An experienced honest mechanic will give you a minimum realistic price before starting the work. A questionable shop will give you the minimum possible price, even though they know that your car will almost certainly need more than what they included in the quote. When calling repair shops for price quotes, be aware that....
No matter what the quote, expect it to go up, at least a little bit. We aim for “minimum realistic”. We include the things that are usually needed based on our experience with other head gasket repairs. However, we don’t have a crystal ball, and we won’t know that the head is damaged beyond repair, or one of the rods is bent, or if the deck surface is unacceptable due to cylinder liner lifting until we take it apart.
Price quotes will differ greatly in several important areas:
Services included – Removing all required components to remove the cylinder head and replace the head gasket (obviously). Disassembly of the cylinder head. This isn’t necessary to replace the gasket, but it is necessary to clean all cylinder head components, inspect head casting(s) for cracks, check valve guide/stem wear, and inspect valve seat condition. Many vehicles have 100k miles or more by the time a head gasket replacement is needed resulting in a fair amount of wear on the valve train components. Aluminum OHC heads should be checked for flatness in two places: across the face of the head with a straight edge, and down the OHC cam bores. Straightening if required and resurfacing the cylinder head, with the wide use of MLS head gaskets by many auto manufactures surface finish requirements (Ra) and flatness play a big role in sealing ability of the head gasket. Many shops do not include rebuilding the cylinder head(s) in the initial quote. At 5 Star Auto Care we always include this. Our in house machine shop allows us to provide this service on every head gasket job we do to restore the cylinder head(s) to like new condition before installation.
Parts replaced - Head gasket repair usually involves replacing other maintenance items and needed or damaged components as well; ask what parts the price includes.
The Quality of parts used - Using high-quality parts is extremely important. You will not save money in the long run by opting for cheaper parts. Low-quality parts can cause damage to many other engine components and often result in having to have the same repair done twice. We use high-quality parts and do the job right the first time.
Warranty provided - The warranty will depend on the quality of parts and the confidence the repair shop has in the skill and expertise of their mechanics. Always ask if the warranty includes parts and labor.
Final thoughts - Hopefully I’ve answered some of your questions about this type of repair, but reading an article is no substitute for communicating with your mechanic. With large projects it’s very important that everybody is on the same page. Take your time to ask questions about the required repair and make a considered decision.