What Breaks When – 6.4 Powerstroke

Written By: Lawrence “LT” Tolman

In 2008, the new 6.4-liter Powerstroke V8 shocked the competition with an output of 350hp and 650 pounds of torque. It was a radical departure from the old 6.0, and the main difference between it and any other engine in its class was the use of a compound turbocharger setup which gave the 6.4 tremendous low RPM torque and throttle response while it was able to maintain great high RPM power, making the 6.4 liter V8 a very well-rounded powerplant. As impressive as they were in stock trim, when you made a few simple modifications to the exhaust and added a programmer, the combination of the high capacity K16 injection pump and twin turbochargers made the 6.4 a serious hot rod contender. With some race-only tunes and a free-flowing exhaust, it was easily capable of producing an extra 300 horsepower over its baseline. At the time, no other diesel was able to make that much extra power with so few changes, and even with modern trucks, a 300hp gain from a tune is hard to match.

The new powerplant was celebrated at first, but 2008 also marked the first year of a new level of federal emission regulations, which meant all ‘08 and newer trucks had to be equipped with a few extra bits to make sure the exhaust coming out of the tail pipe wasn’t harmful to the planet. While the new engine created much less pollution than earlier models, it came with a cost: a sharp decrease in fuel mileage and a whole host of other side effects. Today, the newest 6.4s are nine years old, and by now there are several well documented issues to look out for. In this installment of What Breaks When, we’re going to cover the most common failures, symptoms of the problems, and how to keep that 6.4 running on the road for many miles to come.

Emissions Overview

In order to comply with federal regulation, the 6.4 was fitted with two major and several minor emissions control devices. The two players we’re interested in are the Exhaust Gas Recirculation (EGR) and Diesel Particulate Filter (DPF) systems. The DPF is part of the exhaust stream and is essentially a reusable filter which collects soot. Once enough builds up, the soot is burned off in a regeneration process, turning the harmful chemical compounds into water, nitrogen, and oxygen. That sounds simple enough, but the regen process can be detrimental to your 6.4. Once the soot threshold is reached, the computer injects extra fuel during the exhaust stroke when the valves are open. The raw fuel then travels out the manifolds, through the turbine of both turbochargers, into the downpipe, through the catalyst and finally into the DPF where it burns at temperatures around 1,100°F. In this extreme heat, the soot breaks down, the filter is cleaned, and the whole process starts over.

This extra fuel and heat can cause a few problems while on its way to the DPF, and first is diluted engine oil. Based on simple physics, not all of the fuel is able to make it out of the combustion chamber; there is always a residual amount which collects on the cylinder walls, and it will eventually drip down into the engine oil. Since diesel fuel has much less lubricity than a diesel engine oil, you don’t really want it in your oil, and if too much gets in there, it can cause bearing wear and excessive scuffing of the cylinder walls, and if left un-checked, the fuel in the oil could lead to a catastrophic engine failure. So, the first lesson of owning a 6.4 is to frequently check the oil level on the dipstick, and if you notice it’s too high, change the oil and filter. While Ford recommends six months or 10,000 miles, this can allow too much fuel to build up in the crank case, so it’s a much better idea to follow their “severe duty” schedule and swap the oil out every 5,000, just to keep the fuel dilution to a minimum. And it never hurts to run a premium oil like Schaeffer’s Supreme 9000 5w-40, which is formulated to operate in extreme conditions, especially like engines which use EGR and DPF.

The frequency of regeneration varies with usage of the truck and the quality of fuel you burn, but usually once every fill-up the 6.4 will cleans its exhaust filter. However, this process cannot go on forever. Eventually, the DPF will lose its efficiency and will no longer be able to clean itself out with the normal regen process. Again, it depends on how the truck is used, but this happens at the soonest around 100,000 miles, but can be delayed until near 200k. When the DPF is starting to fail, the first sign will be much more frequent regens, which take a lot longer to complete, and a sharp decrease in fuel mileage. You could go to a dealership for a stock replacement, have yours removed and professionally cleaned, or exchange it yourself with a quality unit from Alliant. Its a simple, bolt-in, no headache replacement that features a two year warranty.

Leaky Radiator

The cooling system is enormous on the 6.4, and for good reason. Since so much extra heat is generated by the emissions systems, there needs to be enough capacity to remove all that extra heat and keep the engine operating at the right temperature. Ford installed a massive radiator, and a cooler for about every other fluid system known to man. The engine radiator, however, has a big flaw: the aluminum core and plastic end tanks are crimped together, and the connection is sealed with an o-ring. While it works well for a while, over time the heat cycles and vibration from the engine will eventually cause a leak. The first tell-tale sign of a failing radiator will be small drips of coolant coming from the grille area, right behind the bumper. If you don’t catch the first warning sign, the low coolant light will eventually come one, and if you still don’t catch the issue, you’ll run the engine out of coolant, and cause some massive headaches. Parts-store radiators will be made with the same design, and even though they might come with a lifetime warranty, the problem hasn’t been addressed. A true upgrade would require eliminating the failure point, and Mishimoto has just the solution. They offer an all-aluminum radiator, and instead of a crimp, the tanks are welded directly to the core. It’s a 100% bolt in design and has a greater fin density which means it will pull more heat from the coolant, keeping your 6.4 running at the right temp, and leak free for a lifetime.

Gallons Per Mile

So, you got a great truck which you’re in love with, but she’s got a drinking problem? Well, sadly that’s the story of just about every 6.4 Powerstroke. While competitors of the time could achieve between 18 to 21 MPG on a good day, most 6.4 drivers reported a best of 14 while driving like grandma on the way to bingo, but if do a lot of city driving, you can expect that real world number to be much closer to 11 MPG, and if you tow frequently you might not even see double digits. At the time when the trucks were new, many drivers found when certain parts of their exhaust fell off, oddly, the fuel mileage drastically increased. While that does sound tempting, we always recommend keeping all factory installed systems in place, and there are ways to improve a 6.4’s fuel mileage without tampering with any parts of the truck that Uncle Sam needs you to keep. The first step is getting your thirsty girl to rehab and giving ‘er a breath of fresh air.

To improve engine efficiency the right way, we’ll start by improving on air density. The stock air box and filter does a good job at keeping any induction noise to a minimum and trapping every last little bit of dirt, but the flow numbers aren’t the best. By swapping to a cold air intake like an S&B you can keep the intake air a couple degrees cooler, and the less restrictive tubing will allow a greater volume of cool air into the turbos. Remember kids, cooler is better.

Next, the air passes through the turbocharger and gets compressed, (twice on the 6.4) and as a result, heated up. While warmer, less dense air is the opposite of what we want, that’s just the laws of physics. However, once it leaves the turbos, we can add some air density back into the equation with a more efficient Banks Technicooler. This bolts in place of the stock intercooler, but will allow more airflow across the core with less pressure drop, will pull more heat out of the charge air, and of course support an elevated boost level over stock.

The Bullydog DPF will go a long way towards making a free breathing and efficient 6.4, but there is one more part of the exhaust you can switch out. On an emission intact truck, the DPF and DOC act as a muffler and cancel a lot of sound from the engine, which means the stock muffler can go away without the risk of being too loud. In its place, you can install a larger 5” Magnaflow DPF Back exhaust, which will look and sound better than stock, and finish up the airflow changes to your 6.4. By making these few simple changes and creating cooler, denser air for the engine, and removing restriction from the exhaust, any diesel will see the benefit of improved fuel mileage, more horsepower, and of course lower EGT’s, all while keeping the emissions systems fully operational.

While airflow changes will make a big dent in the fuel mileage problem, there is one more angle of attack; some changes to the calibration in the computer can help with the fuel drinking problem as well. A good tuner like the Edge Evolution CTS3 will act as a gauge and scan tool and add some power, but will also make a difference in the fuel mileage which might justify keeping your 6.4 on the road for a few more years to come.

Siemens K16

While GM and Ram both relied on Bosch for their high-pressure pumps, Ford took the road less traveled and called on Siemens to supply their injection pump. From a performance standpoint, the K16 is pretty remarkable: while it does run at a slightly lower rail pressure than the Bosch CP3, the K16 is able to deliver a much higher fuel volume, which is part of the reason the horsepower gains on a 6.4 can be so enormous. However, its not all sunshine and rainbows. While the CP3 will take just about any fuel you feed into it, the K16 pump is very picky. At just about any filling station, a very small amount of water can be found in the fuel. Ford took precautions against this, and on the frame rail they installed a small fuel pump and water separator/filter assembly which is designed to take the moisture and dirt out of the fuel system. Even with regular service, there can be a small number of contaminants that’ll pass through the stock HFCM (horizontal fuel conditioning module) and will make its way to the K16. Since the injection pump is made with such high tolerances, any amount of water or dirt that is present can cause the formation of rust or pitting on the inside of the pump which can lead to the untimely failure of the K16. Much like the Bosch CP4 that came later, a failed K16 pump is bad news for the rest of your fuel system and could require replacing EVERYTHING fuel related. The failure isn’t necessarily caused by mileage alone, so it can be prevented.

The stock HFCM does a mediocre job at cleaning the fuel, but there are much better ways to keep water and dirt out of your K16. A FASS Titanium Signature Series lift pump does the exact same thing as the Ford HFCM, only much better and more reliably. It will not only remove the dangerous water and dirt from your fuel, it will also remove any entrapped air which leads to better fuel mileage. The best part is you can get rid of the failure prone HFCM and the pain-in-the-butt filter changes which always leave your arm drenched with fuel. In addition to a lift pump, regularly adding a fuel additive like F-Bomb can give your 6.4 a longer lease on life, since it will disperse any water, clean the fuel entire system, add lubricity to the fuel (which the K16 will thank you for) and add cetane, which means more power, more mileage, and longer life. Also, while it is rare in most parts of the country, don’t run any fuels that have greater than 5% bio-diesel blend in your 6.4. They don’t like it.

Hot Oil

Mounted in the valley of the 6.4 engine in front of the turbochargers, is an oil cooler. It has two separate passageways inside, one for engine oil, and the other for engine coolant. The liquids pass through a small opening and are separated by thin pieces of aluminum. A transfer of heat takes place, so the engine oil is cooled down by the engine coolant, and if everything is working perfectly the temperature of both fluids should be within a couple of degrees of each other. Due to passage of time and lack of maintenance, rust and corrosion can build up in the coolant system and will eventually clog the tiny passageways inside the heat exchanger. This means coolant flow is restricted to the rest of the engine, and since no heat transfer is taking place, the temperature of the oil will skyrocket. And if you know anything about oil, you’ll know warmer oil is thinner and chemically breaks down much quicker, which is not what you want.

The question on a 6.4 is, how do you know if your oil cooler is getting plugged up? The first trick is to use a scan tool like the Edge CTS2 and log engine oil temp and engine coolant temp and see if they are within 10° F of each other. If they are, you’re in the clear for now, but if they are greater than 10° apart, sooner or later you’ll likely get a check engine light with a PO12F temperature correlation code, which basically says the oil is getting much hotter than the engine coolant. If you see this code, chances are your cooler is clogged, and the only permanent solution is to replace it.

Since it’s a fair amount of work to replace the oil cooler, it makes sense to install an upgraded unit like the PPE Heavy Duty cooler. It’s a more efficient design than the original, and it will remove more heat from your oil, helping it to last longer. And whether you just installed a replacement, or your original is still working perfectly, a smart investment is to install a coolant filter kit which will clean out any rust and contaminants and prevent them from clogging up your oil cooler. While regular maintenance of the cooling system is generally overlooked, just remember on a 6.4 (or 6.0 for that matter) clean coolant is very important.

Don’t Park It

I’m not going to sugar coat it for you: the 6.4 powered Superduty does have a few issues that need to be overcome if you plan to use it for a long time. While the first 100,000 miles will be relatively trouble free, the longer you own it, the greater the chance you’ll have of little problems showing up. For most owners however, that’s not enough of a reason to trade in the truck, since there are so many redeeming qualities which outweigh the problems. They have a very strong 5R110 transmission, a bulletproof Sterling 10.5” rear axle, a smooth riding radius arm front suspension, some great looking interiors, can make a ton of power, and let’s face it, no matter how bad the 6.4 is, it is still 100x better than the 6.0. At the end of the day, it all comes down to maintenance. If you take care of the issues as they appear, you will have a long-lasting reliable truck. But, if you neglect your scheduled service, ignore warning signs, and don’t make repairs when they’re needed, you certainly can’t expect any truck to last forever. Its just like my old man said… “take care of your truck, and it will take care of you.”