Why head gaskets fail.January 24, 2020
The best way in life to avoid a problem is by determining what not to do instead of what you should do.
This simplistic logic is confirmed daily on the farm by not driving on a wet field; not planting too deep or too shallow, and not tank mixing products in your sprayer without first doing a jar test. The list goes on and on.
When it comes to the farm shop, you do not want a head gasket to fail on any engine, let alone a large diesel in a key piece of equipment.
Head gasket replacement is an in-depth task that consumes a lot of time, money and effort.
If we understand the common causes for head gasket failure and then avoid them, you will be a stranger to what the pistons in all your engines look like, and that is a good thing!
Gaskets today are different
Years back the copper-shim head gasket was commonplace and may have been identified as a soft gasket. This term was used due to the material’s willingness to conform to the surface of both the cylinder head and engine block.
The engines of that era were not very powerful and in turn, the pressure created in the cylinder during combustion did not tax the gasket. But as engine power increased, especially with the introduction of turbocharging, everything changed.
The industry transitioned to composite head gaskets that are made from asbestos or graphite and then to today’s multi-layer steel designs that employ an elastomer or in some applications, an elastomeric gasket that is steel combined with silicone.
The modern head gasket does a much better job of sealing the cylinder not only for combustion pressure but keeping engine oil and coolant in the proper locations.
The new materials do come with the need to use the coolant specified by the engine manufacturer since other formulas can interact and destroy a head gasket if chemically incorrect.
The old, soft gasket was relatively indifferent to the surface finish it needed to seal against but that cannot be said about the current designs.
The topography of the cylinder head and block deck are paramount in allowing the gasket to do its job.
Simply put, the new head gaskets are very robust but are extremely sensitive to the machined surfaces.
If you have ever lifted a cylinder head off an engine block, notably a cast iron one, you know that they are heavy, especially being condensed weight.
It then may be hard for you to grasp that under high load on a modern engine the cylinder head moves, lifts, and shifts. This is the reason for the change is sealing logic and procedure.
The movement of the cylinder head if either excessive or in conjunction with a challenged gasket, results in a failure that can either leak combustion pressure, coolant, engine oil, or a combination of all three.
Once the gasket is violated the only way to correct the problem is to replace it.
How to avoid head gasket failure
If installed properly at the factory, a head gasket can last the life of the engine. Anything less than that in almost every instance points to something either the engine experienced or poor maintenance by the owner.
Due to the eclectic nature of the engine types, styles and designs found on a farm, the following reasons are application specific.
What the farmer identifies as anti-freeze is really engine coolant; it is a blend of glycol(s) and chemical components such as corrosion inhibitors, organic acids, salts, conditioned water and other ingredients. These are identified collectively as the additive package.
Over time and thermal cycles, the glycols do not alter their ability against freezing, but the additive package becomes consumed. This leaves the engine unprotected from chemical attack though it is still guarded from freeze damage.
An additional component of the chemistry is the combination of materials used in the engine that encounter the coolant. In the old days it was only cast iron and the copper head gasket.
Spent coolant results in the degradation of the head gasket material around the water jackets.
Depending on the engine and gasket design, the coolant can then be introduced into the engine oil or the combustion chamber.
When coolant enters the cylinder the first sign is white smoke from the exhaust. If the leak is left unattended, there is the possibility of hydro-locking the engine, especially on restart after being under load, such as pulling a tillage tool.
Historically, most engines will not bend a connecting rod if hydro-locked during crank since the starter is not powerful enough, but if the leak becomes aggressive when running, the engine can break the connecting rod or kick it through the side of the block. In almost every case the engine is now junk.
A head gasket that leaks coolant into the engine oil will present with white sludge on the inside of the oil fill cap or the dipstick tube.
What is especially concerning with a coolant leak into the oil is that it can go unnoticed for quite some time.
It only takes a minute amount of coolant to seriously impact the lubricity of the oil. Countless engines of all types have been ruined by coolant diluted oil.
It is normal to have a large diesel consume some coolant when worked hard due to the boiling and re-condensing that occurs in the cylinder head during heat transfer.
It is a good practice to look at the oil fill cap if the engine seems to use more coolant than normal. This is especially true with today’s longer oil change intervals. Any engine that is run with coolant diluted oil for any length of time will experience an exponential rate of wear and premature failure.
Exposing the engine to extreme heat such as when a thermostat sticks closed, or a hose fails, and it is kept running will have an impact on the head gasket life.
The failure usually results from the cylinder head deck deforming (twisting slightly) and not properly loading the gasket.
In most cases, a “cooked” engine will have the head gasket fail in the area around the fire ring or between two or more-cylinder bores. The highest temperature gradient is found there.
Unless the situation poses a safety concern to humans or animals, an engine with a failed cooling system should be shut off and the hood opened immediately.
If you do not let the cylinder head get too hot, it will not deform, and the head gasket will not fail.
Over boost/over fueling
Engine power is determined by the cylinder pressure produced. If a turbocharged engine experiences excessive boost or fuel, either intentionally through tuning or accidentally due to a component failure, the cylinder head will move.
Under high boost the head can move enough to stretch the head bolts and relax their tension. Once this occurs you will see white smoke from the exhaust.
All farmers love horsepower but it is best to keep your diesel engines at the power level it left the factory with or you most likely will get good at taking it apart.
When replacing a newer style head gasket, you need to confirm the machine shop has and uses a profilometer to measure and create the desired surface finish on both the head and the block.
The gasket manufacturer will identify the value required and if not achieved, it is likely the repair will fail shortly thereafter.