Sealing the Engine: F150 Gaskets and Seals

The valve cover gaskets found on all of the modular Ford F150 engines (dating back from 1997 to the present) are made from molded rubber. Compared to older style cork, felt or a blended valve cover gasket, the modern molded rubber gasket is significantly better. The latter retains excellent shape and sealing capabilities over a broad temperature. The sticky and soft nature of the rubber provides an excellent seal using less compression (bolts don’t need to be torqued as high) thereby allowing the gaskets to be re-used (provided they are not ripped or crushed).

Now, a rubber molded gasket is not totally infallible. Given enough years, miles and heat cycles and they will fail. Evidence of a bad valve cover gasket is oil weeping (or downright dripping) from underneath the valve cover and down the block. If it is time to change the valve cover gaskets on your F150, you’ll be happy to hear they are quite cheap to buy.

The cylinder head gasket of choice for all F150 pickup engines is a multi-layered steel gasket. Multi-layered steel (MLS) gaskets reign supreme in terms of sealing ability, longevity, and reliability. They are constructed from 3-7 layers of very thin steel and are designed to work like a spring under compression. For every ignition event occurring in the cylinder head, the force of the explosion actually lifts the head up a very minuscule amount (thousandths of an inch).

When this happens, the MLS gasket expands upward with the cylinder head to fill the gap and is then compressed back down once the ignition cycle is complete. These gaskets are extremely strong and are well-capable of withstanding cylinder pressures up to 1500 PSI. This strength is clearly evidenced by their use on the turbocharged Ecoboost engines which have elevated cylinder pressures as compared to the naturally aspirated engine models. 

Having said all that, when is it time to change the head gasket? Well, anytime you remove the cylinder head you should replace the gasket. An MLS gasket is actually capable of being reused, however, every single manufacturer recommends against this practice when talking about head gaskets. The only other time you would need to change a head gasket is because the original has failed. Signs of a bad head gasket are reduced performance, low compression, and/or coolant mixing with the oil or fuel.

OK, there is clearly a trend going on here. The intake gaskets, comprised of a lower and upper set, are all made from molded rubber. Of course, the actual shape of the gaskets depends on the year and which actual manifold is used, however, they are all a molded rubber design due to their robust nature as described above.

Now, determining if the gasket has failed can be a little tricky. Reduced performance, erratic idle, vacuum leak, coolant leaking, or being burned; these are all possible symptoms. If there is no visible fluid leak or obvious vacuum leak, you can detect small leaks by using a propane torch. Simply allow the propane to flow out of the nozzle (UNLIT, no flame) and pass the nozzle around the base of the intake manifold while the engine is running. If the RPM picks up, this means the engine has sucked in some of the propane through a break in the gasket and therefore concludes the gasket needs to be replaced. Given the troublesome plastic manifolds of the early model Triton engines, this is a great trick to have in your toolbox.

Exhaust manifold gaskets have a pretty tough job. 1) They need to fill in any surface irregularities between the exhaust manifold and head. 2) withstand the high temperatures generated by exhaust gas. 3) keep the header bolts torque by exerting tension on the head and manifold flange, and 4) survive the friction between the head and exhaust manifold as they expand and contract at different rates. 

Early Triton engines often suffered from exhaust manifold leaks due to poor quality OEM gaskets. These old design aluminum core gaskets would easily burn out, leading to the dreaded burbling sound of a manifold leak. Ford has since replaced these with a composite design that does marginally better. However, the true cream of the crop for exhaust manifold duty is an MLS or graphite gasket. The MLS takes the cake in all categories, however, it requires an extremely prepared and flat mating surface. Graphite gaskets, on the other hand, are not quite as robust in terms of overall temperature limit but do fill in larger gaps and surface irregularities.

Like the valve cover and intake gaskets, the oil pan gasket used on all naturally aspirated Ford F150 engines (4.6L, 5.4L, 5.0L, 4.2L, 3.5L, 3.7L) is a molded rubber design. It does a great job of sealing the oil pan to the block and is only really prone to failure due to age and road grime. A failed oil pan gasket will be imminently obvious as there will be traces of oil on the pan, or if the leak is severe, a puddle on the driveway!

Regarding the Ecoboost series of engines, these motors do not use a gasket at all. Rather, they use a special RTV sealant to mate the pan to the block. It is interesting to note, however, that many 2.7L Ecoboost owners are reporting early on-set oil pan leaks. Ford has released a TSB to deal with this issue. It mainly consists of removing the pan, draining the oil, cleaning the surfaces exceptionally well and re-apply an updated Ford-specific RTV sealant.