The 2008-2010 Ford Super Duty is a beast of a truck, but the engine under the hood is arguably the most polarizing piece of iron ever to roll out of a Navistar factory. Some guys swear by them. Others won't touch a motor 6.4 Ford diesel with a ten-foot pole unless they’ve got $15,000 sitting in a "rainy day" fund.
It’s a complicated legacy.
Back in 2008, Ford was in a tight spot. They had to meet strict new EPA emissions standards, and the old 6.0L—while legendary once fixed—was a warranty nightmare. Enter the 6.4L Power Stroke. It brought common-rail injection and sequential twin turbos to the table, making it a quiet, smooth, and absolute powerhouse. Honestly, a tuned 6.4 can embarrass sports cars at a red light. But that power came at a cost that many owners are still paying today.
The Engineering Marvel That Overpromised
On paper, this motor was a massive leap forward. It ditched the finicky HEUI (Hydraulic Electronic Unit Injection) system of the 7.3 and 6.0 for a high-pressure common rail setup. That meant better atomization and way more control over the combustion event. It felt like a modern engine.
The sequential turbo setup was also a stroke of genius for drivability. You had a small high-pressure turbo for low-end snap and a larger low-pressure turbo to move massive air at the top end. No more turbo lag. Just endless, linear pull.
But then there's the emissions side. The 6.4 was the first Power Stroke to use a Diesel Particulate Filter (DPF). To clean that filter, the engine would perform a "regen" cycle by spraying extra diesel into the cylinders during the exhaust stroke. The goal was to send raw fuel down the pipe to burn off soot.
The reality? Not all that fuel went out the tailpipe. A lot of it would "wash" the cylinder walls, stripping away the oil film and seeping past the rings into the crankcase. This is called oil dilution, and it’s the silent killer of these engines. When your oil is 15% diesel fuel, it doesn’t lubricate the bearings very well.
Why 6.4 Power Strokes Often Die Early
If you ask a diesel tech why they see 6.4s on the back of tow trucks, they'll usually point to one of three things: the fuel system, the pistons, or the cooling.
The Siemens K16 high-pressure fuel pump is a monster, but it is incredibly sensitive to water. If you get a bad batch of fuel and your water separator doesn't catch it, that pump can literally "grenade." When it fails, it sends fine metal shavings (affectionately known as "doom glitter") through the rails and into the injectors. Replacing the entire fuel system is often an $8,000 job because, on these trucks, you basically have to pull the entire cab off the frame to get to anything.
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Then you have the pistons.
Unlike the 6.7 that came later, the 6.4 used a piston design with a very sharp "lip" on the bowl. Under high heat—especially from heavy towing or aggressive tunes—that lip becomes a stress riser. It’s not uncommon to see a 6.4 with a perfect maintenance record suddenly crack a piston at 120,000 miles. It just happens.
The "Bulletproofing" Myth and Reality
People talk about "bulletproofing" a 6.4 like it’s a weekend project. It isn't. While the term was popularized by the 6.0L community, applying it to the 6.4 involves a much more expensive list of parts.
If you want one of these to last, you can't just slap a tuner on it and call it a day. In fact, aggressive tuning without supporting mods is the fastest way to melt a 6.4. True reliability for this motor requires a multi-pronged attack.
- Coolant Filtration: Casting sand from the manufacturing process often stays in the block. A filtration kit keeps that junk from clogging the tiny passages in the oil cooler.
- Upgraded Radiator: The factory radiators have plastic end tanks that flex and crack. An all-aluminum unit is basically mandatory if you live in a hot climate or tow.
- Rocker Arms: For some reason, the rockers on the 6.4 don't get as much oil as they should. Aftermarket versions with better oiling holes can prevent the "ticking" that leads to dropped valves.
- Fuel Filtration: Installing an aftermarket lift pump like a FASS or AirDog ensures the high-pressure pump always has a steady supply of clean, air-free fuel.
Is the 6.4 Still Worth Buying?
It depends on who you are.
If you are looking for a reliable daily driver and you don't want to turn wrenches, honestly, look for a 2015+ 6.7L. The 6.4 is a "hobbyist" engine. It’s for the guy who wants 600 horsepower with just a few bolt-ons and doesn't mind the risk.
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When they run, they are incredible. The 5R110 TorqShift transmission behind them is nearly indestructible, and the interiors of those 2008-2010 trucks were a huge step up in quality. But you have to be proactive.
Change the oil every 5,000 miles. No exceptions. Monitor your "oil growth" on the dipstick to check for fuel dilution. If the level is rising, your injectors are likely leaking or your regen cycles are too frequent.
Vital Next Steps for Owners
If you just bought a truck with a motor 6.4 Ford diesel or you're looking at one on a used lot, do these three things immediately:
- Check the records for a "cab-off" history. If the fuel pump or turbos have already been replaced by a reputable shop, that's a huge win.
- Install a digital monitor. You need to see your EOT (Engine Oil Temp) and ECT (Engine Coolant Temp) in real-time. If the delta between them is more than 15 degrees, your oil cooler is clogging.
- Inspect the radiator support bar. Ensure it isn't rusted or bent, as front-end flex is what kills the radiators.
The 6.4 is a legendary engine, but it's a high-maintenance relationship. Treat it like a race engine—because that's essentially what it is—and it’ll reward you. Treat it like a "set it and forget it" gasser, and it will break your heart.