Mustang Gasket Tech Guide

A gasket is a thin, compressible, sheet-like piece made from various materials (could be cork, metals, copper, fibrous, rubber etc). The keyword is ‘compressible’ because it's this property that makes a mechanical gasket so effective at sealing two surfaces. In the automotive manufacturing world, there will be a difference between mating surfaces. This difference is typically between hundreds-of-an-inch to thousands-of-an-inch, which although very little makes a big difference during the strains and stresses of combustion engine. When you throw a gasket in between these surfaces and bolt them together, the gasket is squeezed and compresses to fill in gaps that are present. When working on an engine, make sure you adhere to the torque specs so the gasket can do its job how it was designed.

Gasket material and construction play a role as well. As mentioned, gaskets can be made of cork, multiple layers of thin metals, rubber or silicone based, fibrous, or any combination of the above. Gaskets can be one piece, two-piece, or more. A simple analogy to think of is a grilled cheese sandwich. When the cheese warms up, I press down on the top of the sandwich with a spatula. The result - the cheese compresses and fills all the space between the two pieces of bread making a delicious lunch! This isn’t the most scientific of analogies, but it should give you the right idea.

We know what a gasket is, but where are they? Frankly, they are all over your Mustang’s engine! Pretty much every metal-to-metal mating component uses a gasket, as well as any place where fluid transfer occurs. The gaskets that you should familiarize yourself with are

• Oil pan gasket 
• Cylinder head gasket 
• Valve cover gasket 
• Intake manifold gasket
• Exhaust gaskets

There are numerous others, but all on that list above are on the should-know-basis. Let us examine each one a little more closely.

This gasket seals the oil pan (where the oil is contained) to the bottom of the block. Without it, oil would seep or spray out as the engine runs. Older Mustangs used a 2-piece, combination cork and rubber gasket, whereas later model Mustangs use a one-piece design. The S550 oil pan gasket is a carry-over item from the 2011-2014 5.0L Mustang. It is a one-piece design and is also made of molded rubber. It should have a pretty long service life. S550 Mustangs exposed to salt during winter are more likely to develop a weeping oil pan gasket, but this would only be after many years and many miles on the vehicle. There are no upgraded versions available in regards to an oil pan gasket – they are all OEM style (which is plenty fine). You would be prudent to replace the oil pan gasket anytime you remove the oil pan given that access to this gasket is significantly more difficult should a re-used gasket form a poor seal.

Diagnosing this gasket is pretty easy. If it is no longer sealing, you’ll clearly see oil around the edges of the pan, on the pan, even on surrounding parts (k-member). You may even wake up to find a nice puddle of oil under the car. In the event you run into any of these symptoms, unfortunately, swapping the gasket is not easy. Usually, the motor at a minimum needs to be lifted off the mounts to give enough clearance, but if you’re going that far, you might as well have the entire motor lifted out.

These gaskets are located underneath the valve covers and prevent any oil from dripping out from under the valve covers and onto the block. They are a one-piece, metallic design. Oddly enough, some oil weeping from the valve covers is acceptable, particularly on older engines (pushrod engines). If you need to replace these due to excessive oil leaking, luckily valve cover gaskets are one of the easier ones to replace. You just need to get the valve covers off (sometimes, this may include taking the intake off as well), and presto, you have immediate access.

According to Fel-Pro, the S550 5.0L shares the same valve cover gasket as the S197 5.0L. Made from a molded rubber, the only time you would need to replace tehse gaskets is if they start to weep or leak. Generally speaking, molded rubber valve cover gaskets are quite robust and are not anywhere near as prone to leaking as an older technology cork or felt style gasket (found on small-block Fords and Chevs). In fact, molded rubber valve cover gaskets can easily be reused if they are still in good shape (retained their form, not completely compressed or dried out

The intake manifold gasket fits between the lower intake manifold and the cylinder heads. Its purpose is to seal the intake manifold to the head, prevent coolant from entering into the combustion chambers, and also to prevent excess air from entering the engine. If you hear a whistling sound near the intake, see residue around the intake manifold or have coolant loss, the intake manifold gasket could be shot. Replacing it involves removing the entire manifold, cleaning the surfaces, and slapping the new one back on.

Often referred to simply as head gaskets, the cylinder head gasket plays a major role in the overall functionality of your motor. The head gasket seals the cylinder head to the block, but it also helps maintain compression and prevent oil or coolant from entering into the combustion chamber. A broken head gasket can greatly affect your engine. Depending on where it is broken, it can greatly lower compression on a cylinder or multiple cylinders, it may lead to the introduction of coolant and oil into your cylinders (not good!), or even cause backfiring. Excessive smoke out of the tailpipes (blue or white), poor engine performance are common symptoms of a blown head gasket. Simple diagnostic tests involve a compression test, or even better, a leak-down test.

Replacing these is a chore, but crucial to engine performance. The entire top end of the motor has to come off to access these, and picking the right replacement can be tricky as well. Depending on your motor setup (compression ratio, naturally aspirated or forced-induction), stock head gaskets may not be for you. You may need some that are stronger in relation to the type of motor you have built. 

Ford changed the cylinder heads on the 5.0L V8 between 2014 and 2015. 2015 and later 5.0L Mustangs have a cast version of the Boss 302 head, which is partly responsible for the jump in horsepower up to 435. As such, the head gaskets from a 2011-2014 Mustang will not work at all. Currently, both Ford Performance and Cometic make a replacement MLS (multi-layered steel) gasket for the 2015-2018 Mustang. 

MLS style cylinder head gaskets are the most robust and reliable type gasket currently on the market for street going vehicles (actually, many racing applications are making the switch to MLS). Made from multiple layers of very thin steel (3-7 layers depending on engine application), MLS gaskets provide an excellent seal between the cylinder head and block. Believe it or not, every time combustion occurs in a cylinder, the head lifts slight (thousands of an inch, but it still lifts). MLS gaskets are manufactured in such a fashion that they act like a compressed spring. When the head lifts during a combustion cycle, the gasket expands to fill the gap and then is compressed again as the head comes back down. 

MLS gaskets are very strong, routinely withstanding cylinder pressures of 1500 PSI, and work well in all climates. For the Mustang, they are the best choice and least likely to burn out, even when using forced induction. From the factory, the S550 is equipped with an MLS style head gasket. The only reason you would need to swap them out would be if one inadvertently fails (very rare), or if you are removing the heads. It has been shown that MLS gaskets, if removed in good condition, can be re-used, although every manufacturer strictly advises against this. Thus, if you are doing some top end work that involves removing a cylinder head, you should replace the original MLS head gasket with a new one. Forget copper or graphite; an MLS gasket is vastly superior. One minor “grievance” (for lack of a better word) with MLS gaskets is they require an extremely clean and flat mating surface.

The final gasket to be examined is the exhaust manifold/header gasket. It seals the exhaust headers to the exhaust port on the cylinder head. This gasket is one of the few dry gaskets, meaning it does not seal against liquid (there are no fluids flowing between the headers and the exhaust ports). It ensures that no exhaust escapes between the exhaust port and the header flange. A leaking gasket will be immediately noticeable, as your exhaust note will greatly change (usually very raspy and loud), and you may notice more powerful exhaust fumes in the cabin.

When changing headers, it’s always recommended to change the exhaust manifold gaskets as well. Header gaskets are interchangeable between all 2011-2018 5.0L Mustangs. That said, my personal favorite header gasket material is graphite. Extremely heat resistant and usually made very thick with a high crush factor, I find graphite header gaskets to give the best seal and last the longest. At the very minimum, you would want a composite fiber/steel header gasket. They too work well combating burnout and blowout. Avoid paper gaskets at all costs, unless you really like scraping up your knuckles whilst doing monthly header gasket changes.

All being said, the gaskets that are installed all throughout your Mustang have an important role. Some are more pivotal than others (like the head gasket), and despite being a cheap part, have a very tough job. Like all components, as they age and the heat cycles and build up increase, engine gaskets deteriorate and begin to leak. There isn’t a definite period to say when this will happen, unfortunately. The best way to keep everything under control is to do a regular visual inspection.