The Truth About the 6.4L Powerstroke (And Why It’s Not That Bad)

So, just last week, we put out a video talking about the relationship between Ford and Navistar International and how things started to go south with the 6.0L Powerstroke, and then things got even worse with the 6.4L Powerstroke. If you look around anywhere online, everyone says the 6.4L Powerstroke is a total piece of garbage, the worst diesel ever made, a throwaway engine, and so on.

But that got me wondering, is the 6.4L Powerstroke really as bad as everyone says it is? Is it really as problematic as people say it is, or are diesel guys a bunch of drama queens? A lot of the common issues you hear about are related to emissions components, but those same components also cause issues in Cummins and Duramax diesels, so what really makes everyone hate the 6.4L? So, I wanted to find out, is it actually as bad as everyone says? And with the right modifications and maintenance, can it actually be a decent engine?

Where Did the 6.4L Powerstroke Come From?

Before we get too far into all the problems with the 6.4L, we should quickly cover where it came from and how it came to be. The 6.4L was designed as a replacement for the 6.0L Powerstroke, which had given Ford a massive amount of problems, to the tune of hundreds of millions of dollars of repairs and recalls.

Ford asked Navistar to build the 6.4L Powerstroke for two reasons: to meet the upcoming emissions requirements, which were stricter than ever before, and to address all the issues that plagued the 6.0L Powerstroke. It’s also worth noting that Navistar and Ford put this engine together in a “rushed” manner.

The new engine featured sequential variable geometry turbos, piezoelectric injectors, and a high-pressure fuel pump system capable of producing over 30,000 psi of pressure. It was a step up from every Powerstroke engine before it in terms of power, and it was one of the strongest engines in its class, producing 350 horsepower and 650 lb-ft of torque.

With Ford promising the new 6.4L Powerstroke to be one of the best and most resilient engines available on the heavy-duty truck market, truck buyers across the US had pretty high expectations. Initially, the 6.4L Powerstroke was a big success, but that success was short-lived. After seasons passed and the miles racked up on 6.4L trucks, the issues started to show themselves. The 6.4L was designed to be better than the 6.0L, but as Ford quickly found out, it was literally worse.

With flashbacks of the 6.0L Powerstroke engine and a growing base of Ford truck buyers becoming angrier by the day, Ford decided to kill off the 6.4L Powerstroke, and in March of 2010, the last 6.4L equipped Super Duty truck was sold. Lasting a brief three years, 2008, 2009, 2010, the end of the 6.4L Powerstroke was also the end of the Ford and Navistar relationship.

After the 6.4L, Ford introduced the 6.7L Powerstroke, which they’ve been using ever since. We won’t get into the 6.7L Powerstroke in this video, but to call it a massive upgrade from the 6.4L Powerstroke would be a massive understatement.

Okay, now that you have an idea of how the 6.4L came to life, let’s take a look at the most common problems.

#1 Diesel Particulate Filter

Without a doubt, the #1 killer for the 6.4L Powerstroke is the diesel particulate filter, also known as the DPF. It’s worth noting that the DPF system itself doesn’t have to be a bad system. You’ll see plenty of other diesel trucks with DPF systems, and while they can be problematic, it’s extra bad on the 6.4L Powerstroke because of how the regeneration mode on works. The job of the DPF is simple: capture excessive exhaust soot, and then once the ECU detects a certain amount of excessive back pressure, the regeneration mode is triggered to burn off everything captured in the DPF.

It works with two modes: a passive regeneration mode and an active regeneration mode. Passive regeneration occurs while you drive normally, but when that’s not enough to burn off the excess matter, the active regeneration mode is triggered. It switches from passive to active regeneration based on the aforementioned back pressure thresh hold. You’ll know when your truck switches from one mode to the other when a message appears on the dash with a warning that says “drive to clean exhaust filter.”

The active regeneration system works by increasing exhaust gas temperatures, also known as EGT, past 1,000 degrees to burn the excess soot out of the DPF. It increases exhaust gas temperatures by injecting diesel fuel into cylinders #7 and #8 during the exhaust stroke, which makes the internal temperatures skyrocket. While this technically works to get the EGTs way up and burn off the soot in the DPF, it causes a whole host of other major issues.

Most notably, this solution creates oil dilution because some of that fuel being injected during the exhaust stroke slips past the piston rings and down into the oil. This decreases lubrication quite a bit, especially because modern diesel fuel is ultra-low sulfur and doesn’t possess the lubricity it used to. But, it doesn’t stop there.

The second problem with this system is that using cylinders #7 and #8 in this manner can cause them to get so hot that the pistons will start to melt. Once the pistons start to melt, compression is lowered, blowby is increased, and the piston itself is weakened and becomes more prone to cracking, if not completely failing. This issue is compounded by the fact that 6.4L pistons are already prone to cracking, but we’ll talk about that later in the video.

The solution to all of this is “deleting” the DPF with either a full aftermarket exhaust or a delete pipe. Something I want to note is that deleting or emissions defeat devices IS NOT LEGAL in the US, or most countries for that matter and the fines for tampering with emissions devices can get up into the millions of dollars. This is all according to Section 203 of the Clean Air Act, so mess with your truck at your own risk.

Rather than fully deleting the DPF, you can even hollow it out, so it gives the impression that it is still there when it really isn’t. If you remove or hollow out the DPF, you’ll need to reprogram your ECU with a tuner in order to get your truck to run properly, and we’ll cover that a bit later in the video as well. Once your DPF is removed and your ECU reprogrammed, you can enjoy increased fuel economy, lower EGTs, and a much longer life span for your 6.4L.

Like I said before, DPF issues are the #1 killer of the 6.4L, but as we just talked about, it’s an issue that you can actually fix pretty easily, although not legally.

#2 Exhaust Gas Recirculation

Next up on the list of problems is another emissions component, this time, it’s the exhaust gas recirculation system, also known as EGR. This system works by feeding exhaust gases back into the intake, to be reburned by the engine. This is done because not everything is burned with just one engine cycle, so to further improve efficiency and use the unburned fuel, it is fed back into the intake system. Unfortunately, the “dirty” nature of diesel exhaust and the fact that exhaust gas is hot cause some major issues.

The solution to the heat problem is an EGR cooler, or in the case of the 6.4L Powerstroke, two of them. The EGR coolers have one job, and that’s to cool down the exhaust gases before they’re reintroduced to the intake. When the system is functioning perfectly, there isn’t anything really THAT bad about EGR systems, but getting them to work flawlessly isn’t exactly easy. The biggest issue comes in the form of exhaust soot clogging the EGR coolers and gunking up the intake tract and the intake valves.

As things become clogged and gunked up, you’ll start to see negative impacts on your fuel economy, increased exhaust gas temperatures, increased coolant temperatures, especially if the DPF is present. Again, just like the DPF problems, the simplest solution is to straight up to remove the EGR system entirely. This is pretty easy to do, thanks to aftermarket companies offering kits that include everything you need, from the EGR cooler block off plates, coolant block off plates, and a new intake elbow. Again though, you will need a tuner of some sort to reprogram the ECU to avoid check engine lights from appearing on the dash of your truck.

Another option is the deactivate the system through tuning. This will close the valves of the EGR to prevent exhaust gases from re-entering the intake system, but just be aware that this can also can issues, mainly in the form of an impact on your cooling system. So, again, another major issue on the 6.4L can be fixed by just deleting it. It’s not legal, but it is totally possible and very common to fix this major 6.4L problem.

#3 Cavitation Damage and Coolant Flow

Just like Anakin Skywalker, the 6.4L Powerstroke does not like the sand people. More specifically, when the 6.4L Powerstroke blocks were made, they were cast in sand. Sometimes, this sand sticks to the block’s surface after casting and through all the cleaning, and after tons of heat cycles and expose to coolant, these sand particles can become dislodged and start to clog up your coolant system. The biggest issue is when the oil cooler becomes clogged with this sand, and when this happens, your oil temperatures rise dramatically.

A simple fix to this is a basic coolant filter that you splice into the OEM coolant hoses. This helps to filter the sand out, and then you can replace the filter every once and a while to remove the sand it captures.

It’s also worth noting that the 6.4L Powerstroke, like some other Powerstroke engines before it, suffers from cavitation damage issues. The most dangerous form of this cavitation damage is on the front cover and can eventually leak water in the oil. Cavitation damage is a multi-source problem, but it’s most often caused by leaks in the cooling system, which causes the system to lose pressure, which then lets air in, and the boiling point of the coolant is reduced.

There are a few simple solutions to the cavitation problem, mostly just keeping your eye out for leaks and then replacing leaks coolant parts as soon as possible. It’s also worth noting that Ford and Navistar became aware of this issue, and a revised front cover has been made to help fix this problem.

#4 Blowby

The next common issue on the 6.4L Powerstroke is blowby. This is simply oil vapor made when cylinder pressure gets past the piston rings and pressurizes the crankcase. This is something that occurs on all engines, with some engines being worse than others. As you probably guessed, it’s something that affects the 6.4L Powerstroke pretty bad. This issue is handled with a crankcase ventilation system that simply connects the oil fill to the intake tract with a hose.

In theory, the solution Ford and Navistar used works just fine, but because the 6.4L Powerstroke has fairly loose piston ring tolerances, there’s quite a bit of blowby. Ultimately, this means there is a lot of oil vapor introduced to the intake system, which then coats the intake tract, slowly fills the intercooler with oil, increases EGTs, and in very rare cases, can be the cause of a runaway engine.

So, what’s the solution? Well, the solution is exactly what you think it is, deleting it. This is done by venting the oil vapor to the atmosphere by rerouting the house away from the intake and down towards the bottom of the truck. You can also use an inline filter in this system, but for the most part, just venting crankcase pressure to atmosphere fixes these issues.

#5 Piston Cracking

Now, let’s look at some internal problems that can’t be solved with a simple delete or reroute. More specifically, let’s look at the pistons, and unfortunately, the 6.4L pistons are designed or constructed particularly well and a very prone to cracking. This is mostly due to poor casting of powdered metal, but also a hard lip on the piston, which collects heat, and poor quality control during manufacturing.

When the pistons crack, compression for that cylinder drops significantly, fuel dilution gets worse, and blowby is increased. If the piston cracks bad enough, it might fail entirely, and then your engine needs a rebuild. There’s not much of a fix for this problem, but it’s certainly less likely to occur on engines that are totally stock. Turning up the power also turns up the heat, so a stock truck is less likely to experience a cracked piston than a modified truck. However, it’s still common in stock trucks.

#6 Head Bolts

Another internal issue that plagues the 6.4L Powerstroke is the head bolts. You’d think after the whole fiasco of the 6.0L’s head bolts and the stretching problem that Ford and Navistar would’ve figured this out, but surprise, surprise, it’s still an issue. While the 6.4’s head bolts are redesigned and much better than the 6.0’s head bolts, they’re still not adequate, especially if you crank the power up.

In all reality, in totally stock form, the head bolts are fine. When you turn the power up, you start to see some problems. More specifically, the heads will start to lift off the block from excessive amounts of pressure, and that will allow pressure into your cooling system, and sometimes the oil and coolant can even mix. The solution for this is upgraded head studs, but this is a full cab-off repair, so it’s definitely something you should install any time the cab is off for any other repair.

#7 Rockers

The last internal engine issue worth mentioning is the rocker arms. Unfortunately, these are well known to wear out prematurely, and that causes a whole host of other issues down the road. Outside of replacing them, there’s really no simple fix for this problem. The only way to band-aid it is with regular oil changes and good quality oil. The first sign of worn rockers comes in the form of a faint clicking noise coming from the intake.

#8 High-Pressure Fuel Pump and Injectors

Moving back outside the engine, the last problem we’re going to look at with the 6.4L is a multi-stage problem, and that’s fueling. The biggest issue is the water getting into the fuel system, and when this happens, things can get pretty bad. Luckily, the 6.4L Powerstroke features a fuel/water separator, which has to be drained as part of your normal maintenance; otherwise, it’s known for clogging with time.

As excessive amounts of water collect in the separator, it will mix with the diesel fuel and turn into thick, grease-like sludge that may clog the drain valve. When the drain valve gets clogged up, the separator will not drain properly, and when it reaches maximum capacity, it will allow water upstream in the fuel system, which then can rust components and take out the injection pump, injectors, and somethings the entire motor.

Luckily, the problem for this is easy to fix. Simply drain the fuel/water separator regularly, and this problem should remain at bay. Unfortunately, though, the fueling problems don’t stop there. The high-pressure fuel pump is a very complex part and uses extremely tight tolerances internally. If any foreign materials make it past the fuel filters, they can kill the pump entirely. The solution is pretty simple, though, simple replace the fuel filters are the correct intervals and don’t skip them as part of your regular maintenance.

On top of that, the K16 injection pump is known for failure any time there is a lack of low-pressure fuel supply from the lift pump. This will generally only happen if you’re making a ton of power and the lift pump can’t keep up, or your stock lift pump just dies with age.

The last thing I want to mention is that some of the Ford trucks equipped with the 6.4L Powerstroke have a flamethrower exhaust. This only applies to engines built in early 2007, and the issue is basically excessive exhaust heat during regeneration. In reality, this problem affected very few trucks, and Ford quickly solved the issue with an ECU update, but it’s kind of funny to think about your truck regenerating and just lighting everything on fire behind the tailpipe.

Non Engine Issues

Really this is a video about the 6.4 Powerstroke engine, but it’s also worth quickly noting some common issues not related to the engine itself. These include death wobble, radiator failure, body mount failure, front axle seals popping, and more. Combine all of this with the fact the 6.4L Powerstroke is a physically massive engine, and most repairs require the cab to be fully removed, and you quickly see why so many people hate these trucks.

Summary

I do want to mention that a lot of the issues we talked about in this video are caused by a lack of proper maintenance. With perfect maintenance, a lot of these issues are kept at bay or at least reduced in severity. Plus, a lot of the problems on this engine can actually be solved by simply deleting them. That being said, this engine is quite problematic and hard to work on, and it’s easy to see why so many people call it a junk engine.