Why The 6.4-Liter Ford ‘Power Stroke’ Diesel Engine Was Such A Pile Of Trash

The internal combustion engine has been around for well over a century. In that time, automakers have figured out how to make powerful, reliable engines that last for hundreds of thousands of miles with the proper maintenance. And yet, despite all that experience, every so often, someone turns out a real clanger. Mention this in the Ford community, and they’ll gladly tell you all about the perils of the 6.4-liter Powerstroke.

When it comes to big diesels, the list of customer demands is pretty straightforward. People want big torque, decent power, and good fuel economy. They also want an engine that’s practical to maintain, and one that will go the distance. A huge figure on the odometer is a point of pride for many truck owners. Having to do major engine-out repair jobs before the six-figure mark? That’s quite the opposite.

Sadly, when it came to the 6.4-liter Power Stroke, Ford didn’t quite hit all of these goals. Instead, there are a number of common problems that can make these engines quite frustrating to run and maintain.

Power Joke

The 6.4-liter Power Stroke had one job. It was introduced in 2008 in the Ford Super Duty, and it was supposed to take over from the infamous 6.0-liter Power Stroke, an engine of many woes. The hope was that it would offer improved performance (which it did, if it worked), while the new displacement would help move it away from the bad reputation of its predecessor.

The 6.4-liter Power Stroke is not actually a Ford design—it’s actually a specific variant of the Navistar MaxxForce 7. The Ford version featured twin turbos in a sequential configuration, and was capable of putting out 350 horsepower and 650 pound-feet of torque in Ford applications. This engine also showed up in a number of International trucks and buses, too, albeit with a different turbo configuration and lower power output.

Despite Ford’s hopes that this would bring a fresh start after the 6.0 (also a Navistar design), it soon became obvious that this engine was plagued with a raft of issues.  The 6.4 would reveal its own list of common failures, from the cooling system to emissions equipment and beyond. These ranged from merely inconvenient, to major problems that necessitated a total engine rebuild or replacement. Indeed, the engine was so bad, Diesel World referred to it as a “throwaway engine,” a “150,000-mile proposition,” and a “ticking timebomb.” Meanwhile, technician site ProSource Diesel noted the engine was “plagued with problems” and that it led to an explosive blow-up between Ford and Navistar (that’s not quite what happened, but more on that later). Hardly a ringing endorsement.

One of the most well-known issues did not directly involve the engine itself, but the radiator that Ford used in the early 6.4-liter models. As was the trend at the time, Ford had used plastic end tanks for the radiators, which proved surprisingly fragile in service. In particular, the crimps that held the plastic  end tanks to the aluminum core were particularly weak. Vibration from the engine and general use would lead to separation or cracks and rapid coolant loss.

As covered by Motor Trend, the solution was simple—fitting an all-aluminum aftermarket radiator would sort the problem. Alternatively, you could fit a core support brace to try and reduce vibration, but this was really only a band-aid fix for what was fundamentally a bad part. In any case, the failures were so common that this severely dinged the reputation of the engine from the outset. Head to the forums—PowerStroke.org, Ford Truck Enthusiasts, even Diesel Technician Society—you’ll find dozens of stories on this issue.

Exhaust up-pipes were also commonly known for cracking and causing exhaust leaks. Typical symptoms included increased noise, poor drivability, and diesel soot all over the firewall. Owners on forums largely split their complaints between strange sounds from the exhaust, and the frustration of learning they’d have to pull the cab off to execute a fix.

Much like the radiators, the solution was swapping to a hardier aftermarket product. Companies like BD Diesel produce alternatives that are intended to be a more reliable option than going with another OEM part.

More serious problems, though, involved the engine internals themselves. The pistons of the 6.4 are well known for developing cracks. They often propagate out from the lip of the fuel bowl in the center of the piston. While this is considered more likely in tuned examples, it happened to plenty of stock engines, too. Stories abound on the forums, from PowerStroke Nation, to PowerStroke Army. Particularly interesting is an early 2010 post from the Diesel Technician Society. When these engines were still knew, the problem was not well known, and a cracked piston was seen as a very strange occurrence indeed. Later posts from more recent years treat this as a regular thing that isn’t surprising in the least.

High mileage and an aggressive driving style don’t help, but cracked pistons can happen to any 6.4 at any time. This problem has an obvious tell—poor running, smoke pouring out of the tailpipe, and excessive crankcase pressure.

When this happens, it’s game over. You’re up for a full rebuild, assuming the damage isn’t so catastrophic as to have trashed the block itself. Indeed, a cracked piston can send debris rattling around the cylinder, or guide hot combustion gases to torch the walls. You’re often up for a full bore and hone in the event a piston lets go in this way.

Indeed, there are plenty of videos all over YouTube documenting this problem. A particularly bad example can be seen in this video from BarnTech:

The issue is often put down to the design of the pistons used in the 6.4 Power Stroke. They have a “lipped” design, featuring an undercut area in the fuel bowl. It’s believed that combustion gases tend to create a hot spot in these undercut areas, eventually causing pinholes and cracks and eventual piston failure.

There is a solution, but it’s not cheap. Some engine builders, like Choate, recommend using “delipped” pistons in a 6.4 rebuild. They have a more open fuel bowl on top of the piston that doesn’t suffer this same issue.

Smog Problems (Smoglems?)

Modern emissions equipment also hurt the 6.4-liter Power Stroke, particularly in the fuel economy stakes. Ford fitted the engine with a diesel particulate filter (DPF) in order to meet emissions requirements, something which has become common in the industry. The problem is that DPFs need high exhaust temperatures to burn off built-up particulate matter over time. If the vehicle is primarily driven slowly or in stop-go traffic, exhaust temperatures remain low and the DPF begins to clog. At this point, the engine must run a “regeneration” cycle where additional diesel is injected to create hotter exhaust to burn off the build up. This kills fuel economy in a big way.

Deleting the DPF is a popular mod with many truck owners, and avoids a lot of these issues. With no DPF, the truck can be retuned to eliminate all regen cycles, which saves fuel and all the associated hassles this causes. However, it’s highly illegal to do, whether you’re an individual owner or running a shop. Deleting DPFs is a great way to get the EPA on your ass in short order, and the penalties are severe. Fines in the millions of dollars are not uncommon.

The DPF causes other issues, too. Many owners will tell you the 6.4 is known for “making oil.” That is, when checking the dipstick, you might find that the engine oil has climbed above the maximum level. What’s actually happening is that diesel fuel is entering the engine oil. The mixing is undesirable, as the diesel fuel compromises the lubricating qualities of the engine oil. The common understanding is that this happens due to the injection of excess diesel on the exhaust stroke for DPF regeneration, with some sloshing down into the crankcase during this process. However, it can also occur due to leaking injectors or seals on the high-pressure fuel pump.

Whatever the cause, if left unchecked, this can cause engine damage. The tell-tale sign is an engine oil level that has somehow climbed above the maximum. That’s the key hint that fuel is getting into the oil and causing a whole lot of havoc. While the stated oil capacity is 15 quarts on a Super Duty with the 6.4, excess fuel mixing with oil can see 20-plus quarts of fluid in the oil system.

Regular oil changes are the way to manage this. Those in the know change oil every 5,000 miles—following Ford’s “severe conditions” service interval rather than the normal guide of 10,000 miles. This is a well-known fact amongst engine builders. In particular, DFC Diesel says that the 6.4 “requires meticulous maintenance to prevent major failures.” It also notes that reliability concerns often center around the complex emissions equipment.

Yes, Fire From The Tailpipe

DPF issues were also linked with a particularly embarrassing recall in the early days of the 6.4’s run. 37,400 Super Duty trucks were recalled due to fears of “flaming tail pipes,” caused by excess fuel leaking into the exhaust and igniting.

Ford caught it early and was thankfully able to rectify the issue quickly. The fix involved flashing the ECU to avoid excess exhaust temperatures that could cause fire and flames. Still, it was a concerning matter that even led to a small grassfire in Texas that was mercifully extinguished in short order, as covered at the time by NBC.

Ford got on to the issue quickly, so the flaming tailpipes are only a footnote in the engine’s troubled history. Still, I was able to find one great video of this occurring all the way back in 2007.  This 2008 model year Super Duty had the 6.4-liter Power Stroke, and you can see the tailpipes blazing away.

It wasn’t just that the 6.4 had a lot of issues; it was also a bear to work on. The 6.4 took up plenty of space under the hood, and a great many jobs required removing the truck’s cab for access. This frustrated anyone who had to work on these vehicles, with complaints common on owners forums. “With even less working room under the hood, cab removal is all but necessary in order for any type of extensive engine work to take place on the 6.4L Power Stroke,” noted Diesel World magazine. “Blown head gaskets, cracked up-pipes, and even high-pressure fuel pump, oil cooler, and turbo replacement can all warrant the separation of the cab from the frame on these trucks.” Even for jobs that didn’t necessarily need the cab removed, it was often faster and more efficient to do so versus wrestling through the hood and wheel wells.

Tuning Potential

There was one thing that did win the 6.4 some fans—its tuning potential. Much of this came down to its fuel system. Out of the box, the 6.4 had a fuel pump and supporting components that were capable of flowing lots of diesel at high pressure. Capable of flowing roughly 20% more fuel than pumps on contemporary Duramax and Cummins engines, it provided great tuning potential. It meant that if you added oxygen (read: more boost) you could make lots more power without having to swap out major components.

Other stout features of the 6.4 engine design helped in this regard, too. The strong connecting rods in the 6.4 were also a boon in this regard, as were the hardy 5R110W transmissions that Ford fitted to these Super Duty models. The engine even featured a single combined bed plate which held all the main crank bearings—avoiding the issues where bearings might shift and fail at higher power levels.

The 6.4-liter Power Stroke is popular amongst tuners despite its issues.

Various aftermarket solutions exist for tuning the 6.4-liter Power Stroke. Most simply involve flashing the engine control unit with a different tune to squirt in more fuel and up the boost. According to DrivingLine, it’s possible to push the stock engine well past 550 horsepower and 1,000 pound-feet of torque with a tune and some minor mods. Of course, it’s worth remembering one thing—the harder the 6.4 is pushed, the more likely it’s going to face problems down the line.

We’re Breaking Up (Yes, It’s Your Fault)

An acrimonious situation between Ford and engine-manufacturer Navistar, began to brew in the 2000s. As covered by Wards Auto at the time, Ford demanded Navistar cover its share of the warranty costs for the 6.4 engine. When Navistar refused to pay, Ford began deducting these costs from its payments to Navistar for engine shipments. A bold move, and one that escalated the situation significantly.

Things got much uglier in February 2007, and the matter soon ended up in court. Navistar had halted production because, in its own words, Ford had “stopped honoring the terms of agreement under which the engines were built.” The company wasn’t afraid to air its dirty laundry, and the official press release made for bitter reading. Navistar takes the opportunity to brag about how good the 6.4-liter engine is, and how the partnership had played a role in Ford’s leading position in the truck market. Take it all in:

Navistar International Corporation announced today that it is suspending production of the Power Stroke® diesel engine that it builds for Ford Motor Company because Ford has stopped honoring the terms of agreement under which the engines were built.

Navistar’s principal operating company, International Truck and Engine Corporation, has been the exclusive diesel engine supplier for Ford’s heavy duty pickup trucks since 1979 and recently launched a new 6.4L Power Stroke® diesel engine that meets 2007 emissions standards while increasing performance, durability and fuel economy.

Ford, using International-manufactured Power Stroke® diesel engines, has enjoyed leadership market share of close to 50 percent for many years. Navistar believes the new Power Stroke 6.4L diesel engines provide Ford the opportunity to maintain or improve this leadership position. Trade editors who have driven Ford’s 2008 F-250 equipped with the Power Stroke® have given it rave reviews.

International currently produces the new 6.4L Power Stroke® diesel engine at its engine plants in Indianapolis, Ind., and Huntsville, Ala., and as a result of the dispute over commercial terms, production of those engines at both facilities will be halted immediately. The Huntsville operation will continue to produce engines for other customers.

Navistar said that it pays its suppliers and employees under contract terms and that it expects Ford to honor the terms of its agreement.

As you might imagine, Ford didn’t take this threat to Super Duty production lying down. Two weeks later, in March 2007, the courts would force Navistar to resume shipping engines. At the same time, Ford would have to pay in full for all shipments while the matter was before the courts. This was vital to keeping one of Ford’s most important production lines running.

By this point, though, the damage was done. Each company was furious with the other, and all the while, Ford’s reputation was taking a beating in the marketplace. In the meantime, further legal issues sprung up around a future 4.4-liter diesel engine Navistar had been developing for the F-150. It would take two more years to solve the matter. In 2009, as reported by Reuters, the two companies settled all lawsuits between themselves, and decided to part ways after 30 long years together in the domestic truck business.  The diesel engine supply contract would end on December 31, 2009, with Ford making an “undisclosed payment” to Navistar to bring matters to a close.

After the legal and warranty disaster that was the 6.4 and 6.0, Ford had to move on. (Note that, though Reuters says “….the two sides had sued each other over pricing and warranty claims related to the current run of diesel engines Navistar has supplied for Ford’s F-Series trucks,” Wards notes “The auto maker sought reimbursement equal to what it said it overpaid for the engines and for financial obligations owed by Navistar as a result of warranty claims tied to the previous-generation diesel engine sold to Ford.” So both engines were involved in the separation).

The Power Stroke name remained, but this time it would be placed on in-house designs instead. The company was eager to put the hellish reputation of the 6.0 and 6.4 engines in the rear view mirror, and many Ford customers felt the same way.

The engine that followed was the 6.7-liter Power Stroke, which was developed in-house by Ford. After the pain of the previous two Navistar-designed Power Stroke engines, it’s perhaps no surprise Ford decided to take matters into its own hands. Compared to the 6.0 and the 6.4, the 6.7 is regarded as a relatively reliable engine with few standout issues.

Ultimately, you could easily say that the 6.4 is a cursed engine. Ford simply didn’t get the reliable replacement it wanted for the 6.0; it just got more headaches, though it didn’t help that it put a bad radiator in the truck, and chose an engine so difficult to work on in the truck’s packaging environment. It’s no surprise that Ford chose to dump the 6.4 entirely and move on to a newer, less problematic design. It’s also wild to think that it — though especially its predecessor — helped precipitate the destruction of a formerly strong relationship with Navistar shortly after the engine’s debut. As it stands, the 6.4 is the subject of many jokes in Ford circles—which are, in their own ways, cautionary tales for anyone considering buying one.

Image credits: BarnTech, AUDIMotive, and Marine Mechanic via YouTube screenshot, Ford