Gaskets and Engine Sealing - Engine Builder Magazine

Gaskets and Engine Sealing

What a difference a century makes. Engine sealing technology has come a long way from the days when motors were expected to leak and drip past the gasket and onto the ground or vent out into the atmosphere. In the early 20th century, when most people were switching from horses to cars, other, more natural forms of waste were often dropped on the roads, so what was a little oil going to bother?

Times have changed considerably and marks on the ground are no longer acceptable. 

Gaskets that leak today are usually about to fail. Gaskets are engineered specifically for an application to provide trouble-free (and leak-free) performance if operated within the design parameters and maintenance is regularly done. But when gaskets do fail, it’s usually due to one or more of several fairly common reasons.

According to Fel-Pro Gaskets Senior Product Engineer Ed Widder, leading gasket related issues include 1) cooling system neglect, leading to overheating; 2) oil contamination/dilution, and 3) inadequate surface preparation.

“A poorly maintained or non-functioning cooling system may cause repeated overheating,” explains Widder. “Depending on the severity of the condition, the head gasket might fail the first time the engine overheats or withstand several occurrences before developing one or more leak paths.”

Widder explains that contamination/dilution may be traced to a failed head gasket or intake manifold gasket. “In an older, carbureted vehicle, fuel could enter the oil if the carburetor wasn’t tuned properly. It’s more common today, however, to find coolant in the oil due to either a blown head gasket or the failure of an intake manifold gasket. In the latter case, the cause could have been a compatibility issue between the nylon-style materials used in many OE intake manifold gaskets and the engine’s coolant chemistry.”

OAT-type coolants can cause some plastic materials to degrade over time. Widder says Fel-Pro addressed this issue by developing its “PermaDryPlus” intake manifold gaskets that feature a stainless steel carrier and a proprietary molded rubber compound that is compatible with a full range of engine chemicals.

Out-of-flat conditions and poor surface preparation are also still prevalent in today’s engine repair market. In addition to these factors, chronic leaks, if left unaddressed, may end up causing significant engine damage. Many consumers aren’t aware that their engines are leaking small amounts of oil or coolant. 

“Fel-Pro has worked to create awareness of this issue through our ‘The Leaker Stopper’ marketing campaigns,” says Widder, which helps to educate consumers on what to look for and why these leaks need to be fixed. The company is planning for the next campaign to launch in April.

Improper installation and removal procedures are also a factor in gasket failures, explains Tim Golema, Mahle’s aftermarket gasket expert. “Not only could the surface be destroyed by grinding material away or by leaving gasket material on a surface, using the wrong chemical is a more common problem. Things like carburetor cleaners have petroleum distillates that leave a non-dry surface. Sealing products depend on friction in many cases, so that brake clean or contact cleaner provides a clean and DRY surface that every gasket manufacturer requires for installation.”

According to Ron Rotunno of Dana, one reason for a gasket replacement is the possibility of a failure in design, materials or manufacturing processes. “With the advent of Multi-Layer Steel (MLS) head gaskets and the widespread use of molded rubber sealing products, this is more critical than ever. Both are great technologies but offer little margin for error in design and manufacture and ultimately, installation.” 

Rotunno recommends that engine builders choose brands wisely: those that manufacture the products that they sell are “your best bet.” He adds that subtle differences between a “good” gasket and a “bad” one are often difficult to detect. For example, “slight variances in the profile of an embossed bead on an MLS head gasket can have a profound effect on how that bead functions.”

As a manufacturer of gaskets, Rotunno says the Victor Reinz brand also recognizes the fact that it “lives in the aftermarket.” He says the aftermarket repair environment, specifically the condition of casting sealing surfaces, are not what they were when the engine was originally manufactured. “Manufacturing for the aftermarket allows us to re-engineer (versus reverse engineer) a sealing component to avoid duplicating the failure mode of the original and be more installer-friendly.”

Mario Rauch, director of technical marketing at ElringKlinger, a gasket supplier for many OEs in Europe, says the trend in gasket design is the same as it has been for several years. He says many gaskets are changing from soft material or compound gaskets to metal or elastomer solutions. “Head gaskets have also become smaller due to ‘downsizing trends,’ which are slowly influencing the U.S. market, too. Consequently, gaskets are more critical – especially in the area between the cylinders. High-quality gaskets with integrated and individual engineered stopper technologies are considered to be state-of-the-art today.”

Multiple Layers

The first generation of MLS gaskets, while an improvement from composite designs, were often made of too many steel layers and didn’t include the modern “stopper” technology that is incorporated into today’s multi-layer steel gaskets.

For example, Widder says early MLS gasket designs for stock replacement applications did not incorporate a stopper layer and often featured more layers than are needed in today’s MLS designs. “The Fel-Pro engineering team developed a unique stopper layer design called LaserWeld, which prevents over-compression of the fluid-sealing embossments while providing an exceptional combustion seal. We have extended this technology from performance applications to a large percentage of our PermaTorque MLS offering for stock engines.”

ElringKlinger’s Rauch acknowledges that gaskets have advanced beyond directly mating steel layers together and the technology is quite advanced. MLS gaskets now have integrated and precisely engineered stopper systems to protect the delicate and flexible bead against cracks. “This stopper system can be designed in a height-topographic layout to make sure that the movements of the parts and the material stress in the system is always under control. The material of the blades is high-quality steel, heat resistant and with a precisely defined flexible spring rate.”

Cometic’s Matt Polena says his company’s “MLX gasket” has an integrated stopper layer for improved combustion chamber sealing. “This integrated stopper layer improves the clamp load around the cylinder without increasing bore distortion. Our MLX technology can be found in many current applications and can be used for any engine with forced induction. The gaskets are available in 3-, 4 -, and a 5-layer design along with multiple bore sizes.”

MLS head gaskets are constructed of multiple layers of embossed stainless steel. These embossments, when stacked in layers, create what is essentially a spring. It’s that spring that allows for recovery magnitudes higher than what a composite gasket is capable of. 

“If I had to point to ‘why MLS?’ It’s recovery,” Rotunno explains. “Today’s engines are lighter, use lower head bolt torque values (to minimize bore distortion), run hotter and make more power than ever before. These factors combine to create unprecedented amounts of head lift and horizontal motion between castings.”

Rotunno says head lift occurs on every engine, “It’s the direct result of the cycling pressure produced in each cylinder. Combustion pressure wants to separate the cylinder head from the block. When that separation occurs, a leakage path can be created between cylinder bores. Luckily there’s something called recovery. In the sealing world, recovery describes a gasket’s ability to recover or spring back and maintain the contact pressure required to seal during periods of head lift.”

Surface Prep

One thing we all know is that the block and cylinder heads need a good surface finish for the gasket to seal properly. But how good does it need to be? Polena and others say rebuilders should use a straightedge and feeler gauge to check the flatness of the block. Surfaces will need to be restored to manufacturer specs if they are not flat or smooth enough.  

Engine builders typically aren’t working with perfect head and block castings and other gasket mating surfaces, according to Fel-Pro’s Widder.  “Our engineers specialize in designing products that will provide a strong, reliable seal in spite of these more challenging conditions. A true OE-style gasket, by comparison, might merely be engineered to reflect the installation environment in the engine manufacturer’s factory. That’s a vast difference in philosophy that can have a significant impact on the engine builder’s work.”

Widder explains that there are a variety of proprietary aftermarket coatings that accommodate a comparatively wide range of attainable surface finishes. “While MLS gaskets typically require a very smooth surface finish, Fel-Pro PermaTorque MLS head gaskets can accommodate finishes of up to 80 Ra, which most machine shops can easily achieve,” adds Widder.

At the OE level, engine manufacturers have made significant strides in eliminating casting porosity, so the quality of castings entering a rebuilder’s shop is likely to continue to improve, which help the sealing capabilities.

Rauch says engine rebuilders should aim for a surface that doesn’t feature any flat areas when installing MLS gaskets. “The topography should not have any flat areas – we need a ‘peak-to-peak’ topography, that is more like this illustration: /\/\/\/\/\/\/\/\/\/\/\/\; and not like this one: /\­__/\­__/\­__/\­__/\­__/\­__,” he adds.

But Mahle’s Golema contends that since not all MLS gaskets are the same, not everyone will use the same measurements. The general consensus is 50 to 70 Ra for MLS, but that is only a snapshot of reality.  He says gaskets with no coating on them may require a surface of 20 Ra. “Be sure you know what you are installing. In addition, clean and dry is critical, but making sure the components not only have the proper surface finish but are flat as well is just as important.”


Gasket materials have continually improved over the years to address heat resistance, tensile strength, conformability and more. Most of the improvement has come from understanding how components work together, which has lead to increased reliability. The new approach is to allow some joints (i.e., head gaskets) to move and not stick together.

Cometic says it has been testing many different materials for the past several years now. “Non-stick/low friction gasket facings have been developed to reduce fret (damage from friction) during the service life of the seal,” says Polena. “In the past, the thought was you wanted the mating surfaces and the gaskets to all stick together. The understanding of how different surfaces interact (different surface finishes, alloys, etc.) has evolved to allow a small amount of movement to exist, instead of trying to prevent it.”

As an example, Polena says Cometic’s MLS head gaskets employ a high-temperature polymer as the primary micro-seal, but it also uses a very thin PTFE (Teflon) coating to allow for the two surfaces to move freely. “For similar reasons, our exhaust gaskets have a graphite based coating. Many of Cometic’s molded rubber components also include a low friction coating today,” he adds.

While materials may have changed, the philosophy remains the same: proper load balance. Gasket makers acknowledge the ways in which they achieve the correct load balance is continually evolving. “How we get there has changed over the years,” notes Golema. “Today the engine component and the sealing mechanism function as one and not independent parts like before. It is not by accident that leaks have been reduced in most modern engine designs. If the engine requires MLS or molded parts, that is what should be sold in the aftermarket.

The polymer material FKM is used for molded rubber gaskets and as a gasket coating. Fel-Pro says it makes a proprietary FKM rubber that is impervious to all types of oils and fluids, properties that make it ideal for intake manifold gasket sealing, where exposure to the corrosive properties of some coolants can cause premature gasket failure. FKM is also an ideal material for head gasket coating. It is conformable enough to seal minor surface imperfections while being dense enough to retain torque, and it can resist high engine operating temperatures.


Gasket installation has also significantly improved over the years, according to Dana’s Rotunno. “Procedures required to install a composite head gasket vary significantly from those recommended for an MLS installation. Molded rubber has largely replaced cork rubber, paper replaced by single layer embossed steel and traditional rubber rotating shaft seals replaced by those containing PTFE. Each is an example of areas where today’s enhanced sealing technologies affect the way we install/re-seal an engine.”

According to Fel-Pro, using RTV on the gaskets with fluoroelastomer (FKM) or silicone sealing beads can cause multiple issues. The sealer can chemically attack the rubber sealing beads and degrade them. RTV can act as a lubricant and cause the rubber gasket to slip out of place and split, creating a higher probability for leaks. Sealants can add thickness, which creates uneven clamping force since the gasket will not be able to seat correctly. Also, RTV can extrude out when the gasket is compressed, and it could end up in an oil or coolant passage and restrict or block flow.

Fel-Pro says that in cases where a sealant is needed for installation of one of their gaskets, a “FIT Form” will be included, along with the proper sealant. But only apply the sealant in the manner and locations directed.

Performance Gaskets

Knowing when to upgrade to a performance gasket is difficult to answer definitively. “For example, in the diesel world, a stock gasket is used with ARP studs,” says Golema. “The rule of thumb used to be when the firing pressure exceeded 1,200 psi on gasoline engines performance gaskets were needed (mainly to protect from detonation problems). The advantage of performance gaskets in most applications is the use of the highest quality material that will provide a quality seal for the longest amount of time.”

Performance engines that exceed the limits of the stock parameters are now moving and twisting far more than they were designed to originally. Cylinder heads are containing more firing pressure and as a result, sealing needs to be improved. The good news is once products have been developed, engine builders are quick to seek out what works best.

“As a general rule of thumb if you are adding horsepower over the OEM specs it is best to upgrade your gaskets while the engine is apart,” says Cometic’s Polena. “For higher boost applications our MLX head gaskets feature an integrated stopper layer for combustion chamber sealing and improved clamp load around the cylinder. Changing the gaskets is a first step upgrade for forced induction applications, but depending on the final build, fasteners should always be upgraded as well when getting into serious performance applications.”

When the components are designed as a system there are not many issues with sealing, concludes Golema.  “Adding more firing pressure is not bad as long as the system can accommodate the increase. One thing to keep in mind: like everything else it has been an evolution. Where there have been issues in the past, many of them have been resolved by the OE or the performance aftermarket.” ν

You May Also Like

Horsepower and Head Gasket Technology

Head gaskets have one of the toughest job in an engine, and now we’re pushing them harder than ever, making it easier to expose the slightest weakness.

Increasing horsepower is all well and good until you blow a head gasket. Theoretically, it will happen at some point. You can’t avoid it forever. It’s like death and taxes. But, like death and taxes, we like to avoid it, and do our best to do just that. With head gaskets, there’s no one factor responsible for preventing it. There are multiple factors that make a difference.

Inside the Development of Frankenstein’s F-Series LS Cylinder Heads

Right away, engine builders knew it was special.

Billet Blocks and Heads vs. Cast Iron

Billet aluminum has a lower yield strength or higher modulus of elasticity, meaning it will flex, or absorb energy easier under tension or stress than cast aluminum, without incurring permanent damage.

Crankshaft Counterweights

Most engines are internally balanced, meaning all weight adjustment is done on the crankshaft counterweights. However, some stock and modified engines require external balancing due to an increased stroke or larger pistons, and the crankshaft counterweights that would be required to offset the increased inertia simply don’t fit inside the crankcase.

Valve Springs

High-frequency fatigue, also known as harmonics, are a ubiquitous challenge in racing engines and can potentially wreak havoc on the valvetrain if left unchecked. Well-designed valve springs play a pivotal role in managing this, ensuring essential stability, and minimizing wear on valvetrain components.

Other Posts

LS Engine Flatout Gaskets

Flatout Gaskets LS valve cover gaskets are available in paper/silicone in 0.60″ or 0.120″ thicknesses or steel/silicone laminate in 0.50″ or 0.100″ thicknesses.

Summit Racing’s Speedmaster Top End Engine Kits

Kits include a pair of assembled aluminum cylinder heads, an intake manifold, aluminum roller rocker arms, cast aluminum valve covers, and gaskets.

The Latest on Lifters

For racing, a common trend to eliminate the problems associated with hydraulic lifters are the use of limited or short-travel hydraulic lifters. A reduction in plunger travel, which is usually about half that of a traditional full-travel lifter, reduces the amount of oil required to fill the lifter, which in turn reduces the compression of aerated oil.

Speedmaster Top End Engine Kit

Kits include fully assembled PCE cylinder heads, intake manifold, valve covers, intake manifold gaskets, roller rockers, guide plates and screw-in studs.