Head Gasket

Head Gasket Service and Repair

Convenience Auto Service in Ann Arbor are your local head gasket diagnosis, service and repair experts.

Do you have a car that constantly overheats, constantly spews dark or white exhaust smoke, or just runs poorly? If so, your problem may be a blown head gasket. A head gasket is a part (made of copper, steel, graphite or asbestos in older vehicles) that is placed between a cylinder head and engine block to form a secure seal between those components to seal and maintain the pressures that build up in the combustion chambers and the cooling system. As you may or may not know, a car’s engine has several gasses and fluids that move within it: anti-freeze or coolant, the engine’s oil, and a combination of air and fuel. Since these liquids serve specific and distinct purposes, they should never be allowed to mix. A properly functioning head gasket keeps the oil, coolant, air and fuel effectively isolated. If these fluids ever combine, you are in for trouble. To repair this problem, the engine must be disassembled. The cost of the head gasket alone may be minimal, but since many mechanical man hours are required to repair it, costs for repair or engine rebuild is high.

Used Subaru Head Gasket
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Professional Mechanic Repairing Car Engine in Garage.
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Head gasket service and repair: The What, How and Why of Head Gaskets

Convenience Auto Service in Ann Arbor, Michigan is your one-stop for head gasket diagnosis, service, and repair. We service all makes and models, but we specialize in Subaru cars.  As Ann Arbor’s Subaru specialist repair shop, we’ve done over 1000 head gasket repairs over the past 15 years. No repair facility, not even the Subaru dealer has as much Head Gasket experience as Convenience Auto. Prior to opening Convenience Auto, Lou Lippert, one of the owners of Convenience Auto was the service manager at the local Subaru dealer for over 20+ years.  We believe that we have more experience and knowledge of Subaru cars than most dealers.

The following discussion of head gasket repair will reference Subaru cars as an example, but this discussion of Head Gasket repair will give you an understanding that applies to most other makes and models of vehicles driving around Ann Arbor, Michigan today.

For at least 30 years, Subaru (Fuji Heavy Industries in Japan) has utilized  an engine  design philosophy referred to in the industry as a “Boxer Engine.”  The connotation is due to the layout of the cylinders.  In a Subaru six-cylinder engine, pictured in the animation below, the engine block is oriented with the cylinders in a so-called “horizontally opposed” configuration. In the cutaway animation, you can see the motion of the pistons pushing out and in with each bank of three cylinders working like mirror images of each other. This resembles the way a fighter moves his fists.

This horizontal orientation is contrary to the way most other six-cylinder engines are manufactured today, with most manufacturers orienting the shape of the cylinders, with the cylinders moving in a more up and down motion.

BMW, Porsche, and Ferrari are some of the exotic manufacturers that have produced boxer-style engines over the past 50 years. There are several advantages of this engine configuration. The most important is the low-profile, which is important in a vehicle with a low hood line. The more compact horizontal profile of the Subaru engine makes for a lower center of gravity and contributes to significantly better vehicle handling in both good and bad weather.

There are many tradeoffs in engine design, and you might wonder why some manufacturers chose to have cylinders that move up and down when the Boxer offers the advantages of low CG (Center of Gravity)?  There are many reasons, but the most prevalent, I believe has to do with gravity and the circulation of oil and coolant through the respective engines. When the cylinders are oriented up and down (V-6 or V-8 engines) gravity is a big help in getting fluids to flow in the correct places, normally from top to bottom as oil recirculates at low pressure.  The primary issue (for fluids anyway) in the boxer engine is that when the engine shuts off, fluids often “pool”  in unwanted places due to the surface tension of the liquid.  A good analogy for this is the way a spilled drink forms drops (sometimes large drops) on a tabletop. Because the tabletop is horizontal, the liquid forms a puddle and doesn’t move.  This illustrates one of the issues with the Subaru Engine. Often, the oil and coolant puddle in the area of the head gasket, and cause degradation of the sealing capability, and hence the ability of the head gasket to seal properly and do its job.

For a more detailed video and explanation of the Subaru Boxer engine, check out the following video:

What is a Head Gasket? Why is it necessary?

A head gasket is a  thin stamped piece of soft metal with an even softer (in this case, black) coating bonded to both sides.  See  Figure 2.  The head gasket seals the junction between the main engine block and the cylinder head. Nearly all modern engines utilize separate castings for the engine block (which holds the pistons in their respective cylinders) and the cylinder head or “head.”

Due to the complexity of the respective block and head,  and the limitations of the die casting (manufacturing) process, to save weight, the cylinder head is often made of aluminum.  The engine block is made of a steel alloy material because it needs to be extremely strong.  You can return to the animation to identify the three parts (bolted together).   Because the engine block and the cylinder head are made of different materials, they have very different properties when heated. As the engine warms up, the two different metals cause the two components to expand (or contract when it’s cold) at different rates. The head gasket fits between the cylinder head and the engine block like meat in a sandwich. It is relatively soft and compliant so that if there is a mismatch when the inevitable hot – cold – hot cycling occurs, the head gasket remains relatively squishy and keeps the mating surfaces sealed tight so that the various fluids don’t cross over into areas where they don’t belong. This is true for both oil and coolant passing into the cylinder head, (to cool and lubricate the head itself)  and back again into the engine block (to cool the oil and coolant so that it can be recirculated). The relative ‘flatness” of the engine block and the cylinder head mating surfaces are also important for a good seal, but more about that later.

 

What makes a head gasket fail?

Look at the two figures above.  On the left is a new head gasket, and on the right is a head gasket taken out of a  120,000 mile Subaru Outback.  On the new Subaru Head Gasket, you can see a uniform black coating around each of the openings, which is the sealing material. Each of the openings seals a passage where oil or coolant passes. The sealing material ensures that the two fluids won’t mix.

In Figure 3,  We zoom in on the lower right corner of the gasket itself. The arrow is pointing to the failed area of the gasket. Due to the pooling of coolant and oil, the compliant (black) sealing material has been dissolved, and as result, the engine oil and coolant were permitted to mix. This resulted in total engine failure in this case. This explains WHAT happened. This is a very typical failure mode. In a properly running engine, the three products of the engine (Oil, Coolant, and Combustion Gas) are kept separate by the head gasket. When it fails, two or more of these materials mix, engine failure results.

Why Head Gaskets Fail

I mentioned ‘pooling’ previously. The various engine fluids form a puddle when the engine is off since gravity isn’t able to act on them to move. When the oil and coolant turn corrosive (normal as they age) the deterioration to the head gasket accelerates.  The protective coating is literally eaten away by corrosion, AND THE SEAL IS BREACHED.  Good maintenance (Change engine oil and coolant more often than Subaru tells you to) is the best way to put off what is almost inevitable with Subaru Boxer engines.

Believe it or not,  poor battery maintenance can also accelerate head gasket issues.

It might be a bit of a stretch to accept that corroded electrical connections have the potential to accelerate Head Gasket Failure, but it’s true. When battery and ground connections are corroded or loose, your alternator is forced to work harder (generate a higher voltage) to maintain the proper battery state of charge.  The alternator is designed to do this as a normal part of its job. However, the downside of this higher voltage is that it contributes to a phenomenon called galvanic corrosion.  Galvanic corrosion (also called ' dissimilar metal corrosion') refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte with a potential (voltage) difference. The higher the voltage, the more accelerated the corrosion.  The older and more acidic the motor oil and coolant, the more accelerated the corrosion.

Now that you know the What, How, and Why, Who should you choose to fix your bad Subaru head gasket?

Convenience Auto is your best choice for head gasket repair in Ann Arbor. We have repaired more head gaskets on Subaru Cars over the past 15 years than any shop in Washtenaw County, period.  Here are some questions you should consider before selecting a shop:

  1. Do they know what they are doing? See evidence that an experienced  ASE certified tech will be working on your car.
  2. Check the warranty. Ours is 3 years / 36,000 , miles. The dealer offers only 12-month warranties on head gaskets.
  3. Make sure that they will machine the aluminum cylinder head before reinstalling it. We utilize a machine shop service to make sure that the aluminum cylinder is machined to the original flatness specification. This is important to make sure the repair will last a long time. The aluminum head tends to warp, especially if your vehicle overheated, even one time. Most shops and the dealer don’t perform this step. It saves money, but it isn’t a quality repair.
  4. Make sure that the newer aftermarket three-layer head gasket is used. It is proven to last longer than the gasket that Subaru originally installed in your vehicle.
  5. Get a written estimate and compare the parts that are going to be used. We normally include machine shop service, timing belt, water pump, cam seals, cam plugs, belt tensioners, and more. These are relatively low-cost items, and because the engine is already apart, the incremental labor is small. Our anticipation of other issues is what allows us to warranty your repair longer than anyone else. When calling around for estimates, most shops won’t include these extra parts, making their estimate look lower. Our estimates include a ‘not to exceed’ number, which means you won’t get a surprise when it’s time to check out.

If you have read this far, you probably have concluded that you have a head gasket issue on your Subaru or other make of vehicle.  Getting this repaired is an expensive proposition, to be sure.  One other thing that is for sure, you don’t want to repeat this repair in another 18 months.  I guarantee that we have more experience and a better warranty than any other shop in Washtenaw County. You might find a better price (I doubt it, but possible) but if you plan on keeping your car another 100,000 miles,  you won’t find a better value.

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