6.0L vs. 6.4L: Which Power Stroke Is Really Better?
After our 7.3L vs. 6.0L face-off went viral on social media, we’ve decided to drag 6.0L loyalists back into the ring for another Power Stroke throw down. This time, the world’s most-hated diesel is up against the 6.4L—an engine that hasn’t exactly been known for being bulletproof in recent years. But while the 6.0L and 6.4L are arguably the most problematic diesel V8s to ever don the Power Stroke name, each engine still enjoys tens of thousands of fanatical followers. For the 6.0L faithful, an underdog mentality combined with a willingness to work on and learn from their engine seems to help them persevere. On the other side of the fence, the 6.4L-for-life crowd was reeled in by the promise of easy horsepower (nearly 600rwhp with engine tuning), and they refuse to give up on the potent platform that brought common-rail injection and compound turbocharging to the Super Duty line.
Still, for other, non-enthusiast types, rampant issues and expensive (and often extensive) repairs led to former 6.0L and 6.4L owners racing toward other brands, back to the trusty 7.3L or into the new 6.7L Power Stroke. Below, we’ll list the pros and cons of each, along with how they stack up against one another in terms of longevity, performance and cost. While you may have heard the laundry list of items that plague the 6.0L, you might not know that a high-pressure fuel system failure or a cracked piston on a 6.4L can each run you upward of $6,000. So which engine is better? We’ll lay out both power plant's wrap sheets and let you draw your own conclusion(s). Hold on... Shots have officially been fired!
Let’s Compare the Hard Facts
|Displacement:||365 ci||390 ci|
|Valvetrain:||OV, 4-valves per cyl.||OV, 4-valves per cyl.|
|Injection System:||HEUI||High-pressure common-rail|
|Factory Horsepower:||325hp @ 3,300 rpm||350hp at 3,000 rpm|
|Factory Torque:||560lb-ft. ('03-'04) @ 2000 rpm
570lb-ft. ('05-'06) @ 2000 rpm
|650 lb-ft at 2,000 rpm|
This is one category where the 6.0L shines. Outside of rare occasions, bottom end failures are few and far between. The pistons and rods hold up very well as the miles rack up and they can even survive in trucks making 800rwhp. As for the crankshaft, it’s secured via a bedplate, so main cap walk is a non-issue (being that the mains are integrated into the cast-iron piece itself). We will note that as these engines age, it’s not uncommon for them to develop a minor oil leak where the bed plate mates to the block, but it’s more of a quirk than a problem.
To be fair, the 6.4L’s rotating assembly is stout. In fact, the connecting rods are much beefier than what you’ll find in the 6.0L and they’ve proven capable of handling more than 900rwhp. Like the 6.0L, the 6.4L also makes use of a bed plate, so crankshaft-related issues are essentially unheard of. However, the factory pistons leave much to be desired. Due to excessive cylinder pressure, age, abuse and a lip design that retains heat, they’re prone to cracking in both near-stock and highly modified applications. Some enthusiasts theorize that the extreme drive pressure created by the factory-based compound turbo arrangement is the most detrimental to piston life.
Game Over for the 6.4L
Primarily an issue in the aftermarket, once head studs have been installed and presumably over-torqued, a thin spot in the 6.4L’s crankcase can crack. The area most prone to cracking is the section in the block between the head bolt bore and the lifter valley (nearest cylinder numbers three and five), where the casting is only 5 mm thick. The problem area is also located right between two water jackets, which means once the crack extends into a water jacket the engine oil becomes contaminated with coolant. The only remedy is a new block and a full rebuild. Thanks to more awareness of the problem in the aftermarket, different head stud installation techniques and lower final torque sequences are now being put to use, which has helped minimize the number of cracked block scenarios over the past several years.
Up top, things are a bit more problematic for the 6.0L. First and foremost, the engine employs just four torque-to-yield head bolts per cylinder (with sharing), the head bolts only measure 14mm in diameter, stretch under higher cylinder pressure and lead to blown head gaskets. Then, when the cylinder heads are pulled to redo the gaskets (and hopefully add head studs), it’s highly common to find numerous cracks in them, especially near the exhaust valves. If the cracks protrude into the valve seats the head is no longer usable—and it happens a lot.
Not that 6.4L owners are immune from finding cracks in their heads, but the issue does seem to happen a little less in these engines. However, a major wear point in the 6.4L’s valvetrain occurs at the rocker arms. Thanks to a lack of oil supply (the only means the rockers have of receiving oil lubrication is through the pushrods), the fulcrum ball is subjected to excessive friction and heat. The pressed-in balls of the rocker arms are also a point of accelerated wear.
The Quiet Killer: The 6.0L’s Engine Oil Cooler
In our opinion, the most problematic item on the 6.0L Power Stroke is its engine oil cooler. The internally-located fluid-to-fluid heat exchanger is notorious for its coolant passageways plugging up, blocking coolant flow to the EGR cooler and causing the EGR cooler to rupture. Believe it or not, more than 90 percent of all 6.0L EGR cooler failures begin with a plugged oil cooler. A reputable shop or a well-informed owner will know to replace the oil cooler any time a new EGR cooler is being installed. An external, aftermarket coolant filtration system, designed to remove large debris from the engine’s coolant circuit, works wonders for keeping an OEM oil cooler alive.
Comparing Emissions Systems
Said to be under-designed by its critics, the exhaust gas recirculation (EGR) system on the 6.0L was never really up to the task of performing reliably. The EGR cooler plugs up with soot and carbon buildup, as does the EGR valve. On top of that, the aforementioned oil cooler failure can lead to the EGR cooler cracking and dumping coolant into the exhaust system—which, thanks to causing a white smoke situation out the tailpipe, is often misdiagnosed as a blown head gasket.
Saddled with even more emissions control equipment than the 6.0L, the 6.4L makes use of both EGR and an elaborate exhaust aftertreatment system that’s complete with a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF). Periodically, the 6.4L enters what is known as regeneration—a process where trapped particulate matter is burned off in order to keep ash levels low inside the DPF. During the regeneration process, additional fuel is injected on the exhaust stroke (some of you know that Duramax applications use a ninth injector to accomplish the same thing). The downside to this is the fact that the cylinders can be washed down with fuel, which leads to the engine oil inevitably being diluted with diesel.
One issue that plagues both 6.0L and 6.4L owners is cracked up-pipes. Due to a lack of flex at the bellows, stress coupled with age and thousands of heat cycles causes them to crack. When they fail, a noticeable hiss can be heard with the engine under load. Leaking up-pipes also test your sense of smell and sight with exhaust fumes making it into the cab and soot accumulating all over the back of the engine, on the firewall and in the transmission tunnel. In our experience, the problem is more common on 6.4L engines and can occur every 80,000 to 120,000 miles.
Problematic Single VGT (6.0L)
“Sticking” turbos are highly common on 6.0L Power Strokes. All of the problems reside in the exhaust side of the Garrett variable geometry turbocharger. Most frequently, excessive idle time or highway (steady-state) cruising causes the unison ring to freeze up due to carbon buildup, rust or a combination of the two. And since the unison ring is the mechanical link that varies the vanes that direct exhaust flow across the turbine wheel, once it’s stuck in a fixed position you either have a truck that’s extremely laggy down low with good high rpm power (vanes open) or one that’s very responsive at low rpm but has no midrange or top-end (vanes closed). By comparison, the compound turbo system on the 6.4L is much more reliable and the factory 52mm/65mm charger arrangement can even support 600rwhp.
6.0L Injection: HEUI
Similar to the 7.3L, the 6.0L utilizes a revised version of HEUI injection. However, unlike the 7.3L, the system used on the 6.0L was wrought with all sorts of issues. High-pressure oil pumps coming apart, high-pressure oil leaks at the stand-pipes, dummy plugs and STC fitting (on ’05-’07 trucks) and injector issues all run rampant in this troublesome, second-generation version of HEUI.
6.4L Injection: High-Pressure Common-Rail
The 6.4L makes use of a state-of-the-art, high-pressure common-rail fuel system, complete with advanced piezoelectric injectors and a high volume K16 VDO injection pump. Unfortunately, as these engines age they become notorious for injection system failures, which unfold in downright catastrophic fashion. Any time contaminants such as water or rust are permitted to infiltrate the high-pressure system, the injection pump can self-destruct, send debris through the rails to the injectors and back to the fuel tank. The chain reaction failure calls for a whole new injection system, a tank flush and usually starts at $6,000 but can easily top $10K if, during the domino effect of destruction, an injector stuck open and torched a piston.
6.0L Injector Issues
While 6.0Ls get a horrible rap for injector failures, most are caused by a lack of maintenance (neglect), improper installation (damaged O-rings, over-tightened hold-downs) or stiction. Stiction occurs when carbon accumulations form within the injector, causing the spool valve (used to allow high-pressure oil into the injector) to hang up or stick. Stiction can lead to a rough-running engine, some pretty nasty cold-starts and over time will actually damage the injector. Switching to a lower viscosity engine oil and/or using an additive such as Hot Shot’s Secret, Rev-X or Archoil can help alleviate and even eliminate stiction.
6.4L Injector Issues
No spool valve or stiction issues here, but if any contaminants make it through one of the 6.4L’s piezoelectric injectors, it won’t be pretty. The ultra-tight tolerances in these injectors (and the entire high-pressure system in general) make them highly intolerant of anything other than fuel. If these injectors are starved for fuel, such as in the event of a failed lift pump, they can check out in quick order. Though not notorious for failure, the 6.4L injector has a busy workload (pulling off as many as five injection events per combustion cycle), so at any point past 100,000 miles they are fair game for failure. We’ve seen a well cared for set go 200,000 and a poorly-maintained set last just 80,000.
|Engine oil cooler failure is rampant||400 to 430rwhp with custom tuning|
|EGR cooler failure is common||Factory bed plate|
|EGR valve sticking is frequent||Factory rotating assembly can handle 800rwhp (nearly three times stock!)|
|Head bolts stretch and lead to blown head gaskets||Most ’03-’07 engines come attached to the tough 5R110 TorqShift automatic transmission|
|Turbos stick||Arguably less expensive to repair than a 6.4L|
|Injectors are plagued by stiction|
|High-Pressure Oil Pumps (HPOP) fail|
|High-pressure oil leaks are common|
|STC on rear of HPOP fitting separates (’05-’07 engines)|
|Dying batteries kill the fuel injection control module (FICM) (which controls precise firing of the injectors)|
|Cab has to come off for most in-depth repairs||550 to 600rwhp with custom tuning|
|Pistons crack with age and/or abuse||Factory bed plate|
|High-pressure fuel system contaminants can wreck the entire system||Factory connecting rods can handle more than 900rwhp|
|Failed injectors can wipe out pistons||Factory compound turbochargers can support up to 600rwhp, long term|
|EGR cooler failure is common||Larger diameter head bolts keep head gaskets from blowing|
|Blown up-pipes (100K is about all they go)||Most ’08-’10 engines come attached to an even tougher 5R110 TorqShift automatic transmission than what was used behind the 6.0L|
|DPFs inevitably fail|
|Oil dilution is constant due to emissions regeneration cycles|
|Radiators are notorious for leaking|
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