Why The 6.0L Is So Unreliable… - Diesel World

And How You Can Make It More Dependable

Perhaps no other diesel engine in recent memory has burdened its owners more than the 6.0L Power Stroke. Thousands of roadside repairs, expensive tow bills, and repeat failures plague the ’03-’07 Super Duty’s. Rumor has it that Ford even entertained the idea of buying Duramax engines from GM for use in its trucks during this timeframe… Powerful, yes. Reliable, no. You can virtually point to any component on the 6.0L other than its rotating assembly and associate some form of poor engineering or premature failure with it. Exhaust gas recirculation system, oil cooler, head gasket, injector, high-pressure oil pump, FICM, and turbocharger issues all run rampant—several of which strike within the first 100,000 miles


To be fair, some 6.0L’s do go the distance, but it’s very rare to find one with a quarter-million miles on the clock and no history of at least some sort of significant repair. In the following pages, we’ll walk you through all of the 6.0L’s common failure points, starting with the most prevalent offenders. Fortunately for all of us in 2020, 99-percent of the 6.0L’s problems have been thoroughly documented by mechanics and addressed by the diesel world’s thriving aftermarket. We’ll conclude with a list of must-have upgrades that no 6.0L Power Stroke should be forced to live without.

6.0L Power Stroke Head Studs

You’re looking at the biggest failure point on the 6.0L Power Stroke. No, it’s not the EGR cooler and no, it’s not the head bolts. It’s the stacked plate heat exchanger portion of the oil cooler assembly that wreaks the most havoc on the engine. It’s notorious for its internal coolant passages clogging and blocking the coolant flow that’s vital for keeping engine oil temperature in check. With the 6.0L’s HEUI injection system pressurizing the engine oil as high as 3,600 psi in stock form (and 4,000 psi or more in high horsepower applications), some pretty serious heat gets generated. Throw in an inability to effectively cool the oil and, sooner or later, you’ve got serious problems.

Ford Power Stroke Oil Cooler

The miniscule coolant passageways within the oil cooler are prone to clogging due to debris present in the cooling system. This debris is made up of casting sand from the block or suspended deposits from using the incorrect coolant for the engine. Oftentimes it’s a combination of both. In blown head gasket scenarios, where combustion gases are allowed to enter the coolant, carbon contaminates also become lodged in the oil cooler’s tiny passages. Once coolant flow through the oil cooler stops, oil temps sky-rocket.

Scan Gauge 2

Unfortunately, a failing oil cooler can go unnoticed for thousands of miles if you don’t have a way to precisely monitor engine oil temp and coolant temp simultaneously (the dummy gauges in the factory cluster won’t suffice). The general consensus is that both EOT and ECT should stay within 15 degrees of each other, but you should start watching things closely once a 10-degree difference between the two persists.

Ford Power Stroke EGR Cooler

Nearly 90-percent of all EGR cooler failures are a direct result of a plugged oil cooler. Because the coolant blockage in the oil cooler also starves the EGR cooler of the coolant it needs to function properly (remember, the EGR cooler is exposed to 1,200 degree EGT or more), the welds on its core eventually rupture. Once that occurs, you’ve got coolant entering the exhaust (or even the intake) and copious amounts of white smoke leaving the tailpipe. Sadly, it’s not uncommon for an EGR cooler failure to be misdiagnosed, where only the EGR cooler gets replaced and the plugged oil cooler goes unaddressed— which predictably toasts the new EGR cooler in short order.

2003 Power Stroke EGR and 2004-2007 Power Stroke EGR

The other 10-percent of the time, the EGR cooler plugs up with soot, carbon, and oil vapor deposits. And for as many updates and improvements Ford implemented on the 6.0L throughout its production run, surprisingly it’s the ’03 style, circular tube EGR cooler that lives the longest (right). This is due to its larger internal passageways. The later, square-shaped cooler employed on the ’04-’07 engines was prone to plugging much sooner (left).

6.0L Power Stroke EGR Valve

Positioned downwind of the EGR cooler and at the front of the intake manifold, the EGR valve routes exhaust gases back into the 6.0L’s intake tract. Rather than some modern EGR valves, which have been located on the hot-side to help cut soot accumulation, it tends to plug up quickly—oftentimes within 20,000 miles. Once the deposits add up, the valve will stick and the truck will suffer from hesitation, excessive smoke, and low power.

Ford Power Stroke 6.0L Intake Air Temperature Sensor

It’s no secret that EGR is a nasty business in diesel engines, coating everything in its path with a sooty, sticky grime that’s nearly impossible to remove. Affected components include the aforementioned EGR valve and EGR cooler, the intake manifold, cylinder heads, and especially sensors. The intake air temperature (IAT) sensor shown here was chock full of gunk after just 19,000 miles, which should give you an idea what the living conditions are like inside the 6.0L’s intake manifold.

6.0L Coolant Flush

Even with a perfectly healthy oil cooler, the 6.0L’s EGR system is extremely hard on engine coolant. On top of circulating through the heads and block, it’s indirectly exposed to exhaust gas temps that often exceed 1,000 degrees F. This is why it’s so important to not only run the correct antifreeze in your 6.0L, but to change it at the recommended interval (100,000 miles/5 years initially, then every 45,000 miles/3 years). Here you can see what an overdue coolant flush looks like (from left to right), with five flushes being required to fully clean out the cooling system.

6.0L Ford Power Stroke Engine Block

Head to block clamping force is extremely important in any diesel engine thanks to the immense cylinder pressure they produce. Most industrial-grade diesels incorporate at least six head bolts per cylinder, which includes both the Cummins and Duramax competition. Unfortunately for power junkies, Navistar designed the 6.0L Power Stroke platform to employ just four fasteners per cylinder (10 per bank). At the factory 325hp rating, this proves sufficient for the most part (although stock trucks that tow heavy can still lift the heads), but adding 160- rwhp through the use of a programmer pushes them to the brink.

6.0L Ford Power Stroke Engine

An even bigger problem than having just four head bolts per cylinder is the fact that they only measure 14mm in diameter. If you’ve spent any amount of time around the 6.4L Power Stroke, you know that they blow head gaskets much less often than the 6.0L (and usually while making 100hp or more). This is because the head bolts were upsized to 16mm in diameter on the 6.4L.

Ford 6.0L Head Stud

Torque to yield head bolts are nothing new, but once they stretch beyond their yield point permanent elongation occurs. At this point the TTY fastener will never have the same clamping force it did when it left the factory. With the added cylinder pressure (i.e. torque) that comes with aggressive tuning, it doesn’t take long for them to stretch enough to allow combustion gases to escape.

Ford Power Stroke 6.0L coolant residue on degas bottle

One dead giveaway that a 6.0L has lost a head gasket (possibly even both of them) looks like this: coolant residue all over the degas bottle. Once a head lifts and compression sneaks by the gasket the cooling system becomes pressurized. To ensure the heads don’t become warped beyond repair, it’s best to pull the heads and fix the issue as soon as it’s noticed.

Ford 6.0L Power Stroke injectors

The 6.0L Power Stroke’s injectors are one area where the failure rate seems to have been exaggerated a bit over the years. While they aren’t perfect, the 6.0L’s injectors are reliable when treated to proper maintenance (regular oil changes and new fuel filters), clean fuel, and fed sufficient supply pressure from the lift pump. However, if coolant makes its way into the oil, they can head south quickly. Believe it or not, a lot of injector-related issues revolve around improper installation (such as a rolled O-ring, over-tightened injector holddown, or hold-downs that haven’t been torque enough).

Ford Power Stroke 2003-2007 Fuel Injector

The primary reason the 6.0L’s injectors get such a bad rap has to do with stiction above anything else. A phenomenon where oil coking causes friction within the spool valve along with hindering oil flow (remember, the spool valve is what allows high-pressure oil to enter the injector), stiction is behind most of the rough cold starts the 6.0L is notorious for. With stiction in the mix, the injectors’ inability to fire properly leads to poor and inconsistent in-cylinder atomization, excess smoke, erratic idle, and failed cylinder contribution tests.

2003-2007 Ford Power Stroke High Pressure Oil Pump

High-pressure oil issues are extremely common on the 6.0L, which was rarely ever a concern with the HEUI-fired 7.3L that preceded it. Even the high-pressure oil pumps themselves fail. For whatever the reason, the HPOP’s on ’03-’04 engines seem to keep operating as they become weaker while later pumps (’05-‘07) tend to either be good or bad. A suspected bad HPOP will fail to build enough injection control pressure (ICP) to start the engine, but it warrants a look at the IPR valve first. If the screen on the end of the IPR has been damaged chances are good that the pump ingested something.

6.0L snap-to-connect (STC) fitting, high-pressure oil pump

One of the more infamous issues ’04.5-’07 6.0L owners face is a hard-start or no-start condition when warm. Nine times out of 10 the culprit is the snap-to-connect (STC) fitting on the back of the high-pressure oil pump that links the HPOP’s outlet to the branch tubes (which route oil into the stand-pipes, and then on to the oil rails in each head). As the branch tubes vibrate and flex, the STC fitting’s two-piece seal sees excessive wear, and eventually begins to leak oil. When the engine is cold and the oil is thick, it starts like normal, but when it’s warm (and the oil is thinner) it won’t fire off again. Adding insult to injury, the 6.0L’s HPOP is gear-driven at the back of the engine under its own cover, which means accessing the STC fitting calls for a healthy amount of labor.

Ford 6.0L High Pressure Stand Pipe

Long crank, no-start, surging throttle, rough idle, high IPR duty cycle readings, and poor performance are all symptoms of a high-pressure oil leak somewhere in the 6.0L’s HEUI system. Oftentimes the leak is traced back to a bad O-ring on a high-pressure stand pipe (shown), a dummy plug, a cracked branch tube, or the aforementioned STC fitting on the back of the HPOP.

Ford 6.0L Garrett GT3782VA Turbocharger

Many of the 6.0L’s drivability complaints are associated with sticking vanes in the Garrett GT3782VA turbocharger. This issue is common in trucks that spend the majority of their time idling, steady-state cruising, or parked in the driveway. When the moveable vanes (which vary the amount of exhaust gases directed across the turbine wheel) aren’t exercised regularly, they can fail to move at all. Turbo lag or zero high rpm power and a P0299 code stored in the PCM are telltale signs that it’s time to clean the turbo.

6.0L exhaust backpressure (EBP) sensor

Functionality of the electronically controlled variable geometry turbocharger is highly reliant on a working exhaust backpressure (EBP) sensor and a clean line spanning from the EBP sensor to the driver side exhaust manifold. If the sensor fails or the line plugs up, an inaccurate back pressure reading is sent to the PCM, a P0470 and/or P0299 code can be thrown, and the turbo’s VGT operation will be hindered.

Ford 6.0L Stock Turbocharger Unison Ring

A seized unison ring is almost always the guilty party in a stuck turbo situation. The unison ring is the component that moves all of the variable vanes at once. When it hasn’t seen its full operating range in a while, rust and corrosion tends to form, causing it to cement itself in one position. In most cases, pulling the turbo and treating it to a thorough cleaning by way of a Scotch-Brite pad and a die grinder is all that’s required to get the VGT fully functional again.

2003-2007 6.0L Fuel Injection Control Module (FICM)

Perhaps the sneakiest killer of 6.0L performance is the fuel injection control module (FICM). Tasked with sending the precise voltage to each injector solenoid in order to fire it, the FICM has to operate at 48-volts at all times, including at key-on and while cranking the engine over. What newcomers and outsiders to the 6.0L world don’t know is that when the batteries become weaker and the engine gets harder and harder to start, the FICM is dying as well. As the driver side of the FICM fails, the FICM will gradually send lower and lower voltage the injectors’ way, all while performance suffers.


It’s common to find hairline cracks in the 6.0L’s cast-iron cylinder heads (and the same goes for the 6.4L’s heads), but once they protrude into the valve seats it’s time to start over. A crack that spans into an exhaust valve seat is usually a hint that the engine saw elevated EGT on more than one occasion, and maybe even a fair amount of abuse.