Why This V10 Diesel Is One Of The Hardest Engines Of All Time To Work On

Two decades ago, Volkswagen was a very different company than it is today. The company wasn’t that concerned with churning out boring family crossovers. Instead, madman executive Ferdinand Piëch-led Volkswagen worked hard to show the world it was an engineering powerhouse. Here in America, one of the most simultaneously alluring and terrifying examples of the Piëch era was the Volkswagen Touareg V10 TDI, a super SUV with a ridiculous twin-turbo V10 diesel engine. Perhaps even more ridiculous is working on the thing. As the Humble Mechanic is about to show you, this engine is a total nightmare to work on and might be one of the least user-serviceable high-volume engines ever made.

Charles the Humble Mechanic is quite possibly one of the best resources in America for working on broken VWs. His videos and advice can help you do everything from removing sunroof cassettes to showing you the inner workings of the infamous W8 engine. Charles’ work has helped me with restoring a B5.5 Passat and diagnosing a bad dual-mass flywheel in a newer Jetta. Charles joined forces with Paul from Deutsche Auto Parts to fix Jason’s wife’s failed Tiguan.

So you can only imagine the look on my face when our Discord server pinged with a notification about a new Humble Mechanic video. As one of the few crazy people willing to own a Touareg V10 TDI today, this video was a fascinating watch, and further proof that I’m totally screwed if my V10 ever finds a serious way to break.

I’ve written about the Volkswagen Touareg many times before, but here’s a quick refresher. Back in the 1990s, Porsche realized it could not thrive on just the 911 and Boxster alone, so it decided it needed to build a high-volume cash cow. Minivans were the hot thing and SUVs were gaining traction. Porsche considered a number of options, including a hot minivan. Ultimately, the brand landed on making a super SUV, first choosing Mercedes-Benz as its partner. That marriage failed quickly, and the brand then pitched the idea to VW’s Piëch, who was just crazy enough to love the project while also wanting a version of his own.

The result was the 2002 Porsche Cayenne and the Volkswagen Touareg, two hopelessly complicated SUVs meant to conquer terrain, tow huge trailers, and go seriously fast all while looking like a gentle crossover. I’ve owned a Touareg VR6, and, as mentioned earlier, I also own one of these V10 TDIs.

These SUVs are known for threatening their owners with bankruptcy, and even I had my fair share of issues with my VR6. My transmission fluid pan rusted through, the plastic gas tank collar cracked, the transmission valve body wore out, and I damaged some unknown steering component while off-roading, making my steering inexplicably harder and softer at the same time.

All of that ignores the other junk such as sunroof drain leaks, the inability to arm the alarm system, and how all four shocks left the chat at about the same time.

Despite all of that, my VR6 was still one of my favorite daily drivers. But you have no idea just how deep the absurd Volkswagen engineering goes until you tear into a hero model like the V10 TDI. Thankfully, I don’t have to!

Charles starts off the video by explaining why the 200,000-mile V10 Touareg was in his hands. This V10 TDI had a camshaft failure, which remains a somewhat common failure point in older “Pumpe Duse” TDI engines.

It’s not a unique failure to the V10 TDI; even the little cutie powering old Jettas had this problem. In a PD TDI, each injector is fed from the fuel rail which is supplied by the medium-pressure tandem pump. When the injectors are actuated by the camshaft, they make up to 27,846 psi of pressure. The fuel spray is also controlled by an electric solenoid.

This means the cams have the extra job of actuating injectors on top of working the engine’s valves. This is why Volkswagen wanted original PD owners to buy its special oil to reduce wear.

PD cam lobes are known to wear faster, and when that happens, the driver may first notice that their engine is louder with perhaps a little more “bass” than usual. If this issue isn’t diagnosed or is otherwise ignored, cam lobe wear may accelerate to the point where engine performance will be reduced. Finally, if the cams still aren’t replaced, the engine’s valves and lifters may experience a catastrophic failure. So, this is a pretty big deal even in a wee 1.9-liter four-cylinder diesel in a Beetle, let alone the big honkin’ 5.0-liter V10 TDI. Sadly, Charles notes, this V10 suffered from a cam failure hard enough to become dead, and we’ll see the aftermath in a bit.

Charles jumps right in by explaining that firstly, the V10 TDI engine is shoehorned into the engine bay of the Volkswagen Touareg with basically no space to spare. You can work on a few parts, like the tandem pumps or the starter, without removing the engine, but the vast majority of the time you are dropping both the engine and the transmission. This means that many repairs automatically start off at least a few thousand dollars before you even talk about what needs to be fixed.

Charles shows that this isn’t a walk in the park. The drivetrain is dropped from the vehicle whole onto jacks strong enough to support the 485-pound engine plus transmission, then the body is lifted away. I can’t imagine trying to do this in a garage without a lift. Charles then notes that an immediate curveball is in the V10 TDI’s design; normally, Volkswagen powers the accessories like the water pump and the alternator through a serpentine belt on the front of the engine. That’s not the case here.

The V10 TDI is gear-driven, with the accessory drive at the back of the engine, which is great because it avoids forcing a poor owner to drop the engine just to replace a belt. Yeah, it’s legitimately that tight in the engine bay. You can also hear the gears at work when the engine is running, and I love the mechanical symphony.

In this case, it also makes tearing down the engine a bit more interesting.

Charles discovers failed exhaust flex pipes before tearing into the top of the engine to reach the camshafts. At first, things look like you’d expect a nearly 20-year-old German car to look like. The sheathing around the wires on the engine easily crumbles away, and there’s a mountain of components to get through. As Charles is ripping chunks off of the engine, he confirms what I said earlier about how the V10 TDI has two of everything. That means two ECMs, two sets of pipes, a turbo for each bank, two high-pressure pumps, and a ridiculous harness to make all of the doubled-up bits work. If you plug an advanced scanner into a V10 TDI, you’ll see that the car sees itself as two five-cylinder engines rather than one V10.

As Charles continues churning away, he discovers soot-caked parts and fasteners that have stripped out. All of this is bad, but what’s worse is the labyrinth Volkswagen forced technicians to fight through to repair this engine. Charles had to go through various harnesses, brackets, and different forms of fasteners to get through all of these parts. He notes that these parts also have to go back on in order. If you forget something, you basically have to hit reverse and take off everything until you get back to the part you skipped.

Oh and as for tools, Charles jokes darkly “every tool ever invented,” so that’s fun. Charles then says that while an air-cooled Beetle has perhaps the most serviceable engine ever made, the V10 TDI has to be the least serviceable engine ever made.

Charles eventually gets through everything on top of the engine, including chunks of soot, and gets to the cams. Sure enough, the lobes have been rounded out, which means the valves aren’t opening all the way.

At this point, Charles gives a rough estimate for what it would cost to replace the cams and the lifters. You’d be looking at around $3,500. Mind you, that’s not including the cost to drop the drivetrain or the cost to replace all of the other stuff involved in this procedure. Yikes.

Sadly, Charles confirms that this engine has experienced cam failure, rendering it inoperable. Since the engine is dead, he’s going to tear it down anyway so we can see a rare look inside of the engine. The wild part? Charles has a long way to go before he can even show us the glow plugs.

Next, we go through the EGR cooler in a long battle to reach the alternator underneath it. In a previous piece, I noted how VW used a hopelessly complicated water-cooled alternator in the V10 TDI, and this is why. The poor alternator is in the valley of the engine located around a lot of hot parts. VW is even using an electronic thermostat in this engine, a part Charles says the V10 TDI shares with the also hilariously complicated Passat W8 engine.

Charles finally reaches the glow plugs, and they appear to be in rough shape, too. A VW with bad glow plugs will still run and drive. However, the glow plugs warm the diesel engine’s cylinders to help cold-weather starting. In my experience, if your VW TDI’s glow plugs are crap your engine may crank and crank before either choking into life or killing its battery. Charles bets this TDI was throwing glow plug codes.

Also, check out (above) what the high-pressure pump looks like inside!

The gear drive (below) is pure insanity. One gear alone runs the power steering pump, and then a shaft extends through an engine mount and allows the same gear to turn the A/C compressor nearer the front of the engine.

The A/C compressor is in its roughly normal place near the front of the engine, but it would usually be driven by a belt, not a weird shaft coming from a gear and the power steering pump in the rear.

Finally, after a ton of work, Charles gets to the gear drive system at the back of the engine and it’s simply a thing of beauty. It looks like a massive timepiece, but = on an engine. We’re also not just talking about accessories either, but the engine’s timing is done at the back of the engine through these gears, too. Forget David Tracy’s love of timing chains, this is the holy grail of timing!

Charles continues by ripping off the cylinder heads and the camshafts out. Something fascinating about the V10 TDI is that it has a sort of tensioner on the gear drive that makes sure the load on the gears is the same no matter the temperature. The gears may very well be the most reliable thing on this engine!

We also get a look at the bad cams as well. A worn cam lobe shows metal missing and the lifter associated with that lobe has a substantial hole in it. Who even knows where that metal went? Hopefully mostly in the filter.

Oh yeah, Charles finally got to the alternator, too. It only took tearing down most of the engine:

The payoff of all of this work is great. Once Charles gets to the end, he finally gets the gear system apart and finds out that the V10 TDI uses 20 gears for timing, accessories, and to make the darn thing just run.

I won’t reveal everything Charles found, but he concludes that the V10 TDI is both wildly complicated, but also really impressive. Volkswagen really did achieve its mission of showing itself to be an engineering powerhouse, and the Piëch Trifecta — that’s the Touareg, Phaeton, and Passat W8 — were halo cars that truly represented it.

Unfortunately, this also means pain for the Piëch era’s biggest fans. Charles suspects that this engine was so far gone that it would have needed at least $10,000 of work to get back into shape, which is shocking since Charles does his own labor. Who knows what the bill would look like at a dealer? As I said in a previous piece, you can get running V10 TDIs for substantially less than that. So, I’m just going to continue to hope nothing terrifying happens with my own V10.

Click here to watch more Humble Mechanic fun. Now I must find some wood to knock on.

(Screenshots: HumbleMechanic on YouTube)