Diesel Engines: Are They Dying?

Hello,
It might be a strange question, but I'm curious whether modern diesel engines always fail due to things like a broken timing belt, or if they ever stop starting because the compression has become too low (which is something I remember from older engines).


Regards,
Martin.

Even today, some timing belts can break, which reduces compression, and theoretically, a diesel engine could eventually only start with a fully charged battery. However, in practice, there are people who have driven their Passat TDI (manufactured in 1996) with 90 horsepower for over 500,000 kilometers.

Best regards, WarLord.

Okay, I now have almost 240,000 kilometers on the odometer, and the car has had the tuning chip installed since 90,000 kilometers, and it's still working perfectly! Are you worried about the mileage? I think modern engines, in their standard configuration, have a very high lifespan. An engine designer from a top-tier German car company once said that the wear on the cylinder bore decreases by only 0.01 mm after 1 million kilometers, and that cold engines can be easily 'revved' without causing damage. I can't imagine that, but apparently, it's true. Therefore, I think that compression problems nowadays, if they occur at all, are only found in heavily modified engines. Besides, usually everything else breaks down before the engine itself gives up. (MAF sensor, alternator, turbo, sensors, belts, etc.).

Hello,
'Someone once told me that modern engines are designed in such a way that they theoretically shouldn't wear out or should have very little wear. People worry about driving gently and using the right engine oil, probably more than necessary. I've never heard of a TDI engine failing to start simply because it's worn out. Has anyone experienced this? If so, at what mileage?'
Regards,
Martin.

My last car, an Audi 200 20V with a 100 horsepower per liter engine from its 2.2-liter 5-cylinder, lasted at least 500,000 km, and even with that mileage, it showed no externally visible signs of wear. Everything else had simply deteriorated. The car was then no longer driven, but rather sold off in parts by the buyer. He even sold the engine too!!!

Best regards,
Uwe

Is it true that the typical wear limit for modern TDI engines is certainly beyond 400,000 km (assuming regular oil and air filter changes)?

However, the number of sudden cardiac arrests is worryingly increasing.

Okay, gib mir den Text, den du übersetzt haben möchtest.

In VW T4 vehicles with the 2.5L engine, the water pump often fails, which can cause the timing belt (which also drives the water pump) to break, leading to complete engine failure.

At Audi, they are struggling with broken rocker arms in the V6 TDI engines.

Mercedes is experiencing issues with common rail injection pumps that can seize up if the fuel tank is run completely empty.

'Nowadays, the problems are mainly with the auxiliary components. I haven't encountered any TDI engines that are completely worn out. Not even the Sharan taxi with a 1.9L TDI engine and 400,000 km has starting problems.'

Therefore, even a reasonable amount of tuning won't cause any significant problems for the engine. The reserves are more than sufficient, even for larger performance increases.

Best regards,
Uwe

Hi! The thread title implies that 'older' diesel engines had a problem with premature failure.

That is absolutely not the case!

I'm only thinking about the Daimler pre-combustion engine in the 200D (OM615?). It had a timing chain that lasted a lifetime, an engine oil-lubricated inline pump, and no turbocharger. So, 'sudden cardiac arrests' are ruled out!

Apparently, former German-made taxis (W123 models) are still being used as taxis in Egypt, and some of them have accumulated mileage exceeding 1 million kilometers.

The biggest weakness of today's TDI engines, in my opinion, is the poorly designed timing belt system, followed by the limited lifespan of the turbocharger, then the ESP (Electronic Stability Program) system, and various sensors/actuators. The actual 'heart' of the engine, i.e., the crankshaft and cylinder block, could potentially last as long as the OM615 engine.

Based on a well-designed system, it should be easily possible to design a long-life engine that requires no maintenance other than fluid and filter changes, and still comes with a factory warranty of 500,000 km for trouble-free operation.

But that is probably not in the economic interest, and it also doesn't really fit into our throwaway society.

SeatArosa1.7SDI wrote:

The biggest weakness of today's TDI engines, in my opinion, is the poorly designed timing belt system.

"... Please, for once, abandon your completely ridiculous (and incorrect) opinion that the ZR is a flawed design."
Do you know the internal company statistics regarding bearing failures and chain failures?
No... I already checked, and it doesn't look good for the chain.
Even a chain is not wear-free or maintenance-free, and it is just as sensitive as the timing belt.
Würdest du die Belastungen der heutigen Motoren den Ketten von einem OM615 zumuten, wäre diese Kette schon in 15tkm kaputt ... Rcareless.
Modern HD injection engines (whether common rail or pump-injector) simply destroy everything. The forces generated within them are immense, while the older VK engine was much gentler on its surroundings.
Do you know the maintenance instructions for the timing belt on a 1979 VW 827 WK diesel engine? Apparently not. There are none. The timing belt doesn't need to be replaced, and I know of engines like this that have reached 500,000 km.
When comparing engines, make sure they are from the same engine family, such as comparing the OM615 with the older WK-D 827.
The last DC CR diesel engine had enough problems... most of them stemmed from the chain and the CR pump.

Unfortunately, our current emission regulations no longer allow for engines like the VK/WK engines you are requesting.

Come back from the past and get real!

SeatArosa1.7SDI wrote:

... Apparently, former German-made taxis (W123 models) are still being used as taxis in Egypt, and some of them have accumulated mileage exceeding 1 million kilometers. ...

The currently oldest confirmed DC diesel-powered passenger car is located in Sindelfingen and is a Greek taxi with 4.6 million kilometers and 11 engine replacements.
That results in a mileage of 420,000 km per engine replacement. In my opinion, that's not a lot.
However, only two engines were actually involved in this "engine frenzy," and they were repeatedly reworked and swapped out.

http://www.autokiste.de/start.htm?site=/psg/0409/3547.htm

... Finally, please abandon your completely nonsensical (and false) opinion that the ZR is a design flaw.

Where a part costing only €30 is used for such a fundamentally important function (the phase-locked synchronous rotational movement of the clockwise and counter-clockwise components), the failure of which can lead to a complete economic loss of the entire engine, one can certainly speak of at least negligence in the design. A part that requires frequent maintenance is, of course, not particularly reliable compared to other, maintenance-free methods. Have you ever seen a timing belt in a fundamentally important location on an aircraft engine?

Do you know the internal factory statistics regarding bearing failures and chain failures?

'What I experience through my five senses is enough for me. And you rarely hear about complete chain failures, unlike TDI timing belts (especially those connected to the water pump).'

Even a chain is not wear-free / maintenance-free.

If you're looking for something that requires regular oil and filter changes, inspections, and tightening, then no, it's not maintenance-free.

and it is just as sensitive as the ZR.

I would like to disagree with that, assuming the prescribed maintenance intervals are followed.

If you were to subject the chains of an OM615 to the stresses of modern engines, those chains would fail in just 15,000 km...

No one has ever talked about adapting an original OM615 chain to a TDI-PD engine.

Unfortunately, our current emission regulations no longer allow for engines like the VK/WK engines you are requesting. Please come back to reality from the past!

I haven't mentioned anything about the 'pre-chamber' combustion process, which is only indirectly related to the valve control system.

Perhaps you misunderstood my example with the timing chain, thinking that I consider it the ultimate solution and the best way to go. However, that is not the case. Rather, I criticized the timing belt drive in such a critical area. What bothers me is that many technically sound TDI engines have to fail prematurely because the priorities in the design shifted from 'longevity and reliability' towards 'low manufacturing cost,' 'low operating noise,' and 'weight reduction.'

My reservations can actually be reduced to two basic problems:
1.) Minimize the residual risk of a total loss. So-called 'free-running' engines for gasoline engines meet this condition, as a collision between an open valve and the piston is not possible due to the design.
2.) Avoid high maintenance costs/high effort. This problem is only partially solved by free-running belts (which are only common in gasoline engines), as the belt can be driven until its natural end, but then a potential failure must be accepted. Solutions here involve more complex designs such as a properly sized chain, spur gears, a lower-mounted crankshaft, pushrods, bevel gears, a constant-velocity joint, or electro-hydraulic valves.

By the way, I dare to claim that, ultimately, a maintenance-free solution (meaning that no machine component needs to be replaced) would be economically worthwhile for the average consumer. If you sum up the costs of replacing timing belts over the lifetime of the product, you have a margin of less than €1500, which would be enough to install gold-plated gears from the factory .

However, as I said, the market and company policies/sales strategies prioritize other things. The fact that they learned from mistakes with the new T5 TDI-PD and are also catering to commercial customers proves that VAG is well aware of the problems.

Regards,
Holger.

Furthermore, to my knowledge, modern methods like PD (presumably referring to a specific engine technology) are no longer feasible with a timing chain. I once read in an engine magazine that timing chains can stretch during their lifespan, leading to a crank angle deviation of up to 7 degrees, which cannot be compensated for in a real-time pressure build-up system like PD. With CR (presumably referring to another engine technology), the injection timing can be shifted to a different point within a wider range using the pressure reservoir and electronic control.

Roger points out that a chain cannot control a PD motor for as long as a timing belt. The "impact" load creates very high torsional forces, which could only be absorbed with a chain that is "generously" sized. However, even then, the problem of chain elongation arises.

Bertil mentioned, when comparing WK and TDI CR engines, that the power required to drive an ESP system today is significantly higher than what was possible with WK engines.

"A free-running valve in a diesel engine... well, I can only imagine that happening to a limited extent, since we're dealing with completely different compression ratios compared to gasoline engines. So, essentially, there's less space between the piston and the valve."

You probably hear a lot about timing belt (TB) failures because there are significantly more engines with timing belts than with chains. And even then, the question is to what extent statistics from everyday life can be trusted. I would question whether someone who heavily tunes their TDI engine considers more frequent replacement intervals for critical components. There's likely a significant "hidden" number of cases where engines "die" in VAG vehicles simply because the driver didn't properly maintain them.

Just a side note... there are actually quite a few aircraft engines that use timing belts (like the DG 800, and so on), which makes sense, as it's all about minimizing weight.

Roger brings it up, a chain cannot control a PD motor for as long as a timing belt. Due to the 'impact' load, very high torque forces are generated, which could only be absorbed with a 'generously' sized chain. However, even then, the problem of elongation arises.

Okay, so let me reiterate this in different words: I compared the aggregate lifespan, reliability, and maintenance requirements completely independently of the combustion and injection methods. The fact that the OM615 has a chain that is not suitable for a TDI-PD configuration doesn't automatically make the timing belt the optimal solution for a TDI-PD.

To put it in broad terms: I would welcome a solution for the NW/valve drive that, within the technical constraints of each individual case, reduces maintenance costs during the lifespan of the equipment to such an extent that the additional purchase costs can be easily offset, and that incidentally also increases reliability and operational safety. A positive example: the new five-cylinder engine in the T5 TDI-PD (solution: spur gears).

Ugh, that was quite a sentence...

PS

You're probably right when you talk about Rotax aircraft engines. However, some of them are still largely based on the "Beetle" design, meaning they have a central camshaft and pushrods.

SeatArosa1.7SDI wrote:

...Where a part costing 30€ is used for such a fundamentally important function (the phase-locked synchronous rotational movement of the clockwise and counter-clockwise components), the failure of which can lead to a complete economic loss of the entire engine, one can certainly speak of at least negligent design.

Have you ever seen engine damage caused by a jammed or broken timing chain?
You'll wish you had a chain tensioner. The flying chain parts are deadly!

Quote:

A component that requires frequent maintenance intervals is, as is well known, not necessarily more reliable than other, maintenance-free methods.

Auch eine Kette hat ein Wartungsintervall. Nur viele wollen das nicht Wahrhaben. Not you either.
DC claims to have a maintenance interval that lasts for the "entire lifespan of the car." At DC, a "car lifespan" is specified as 200,000 km (compared to 160,000 km at VW), meaning that only 20,000 km after the second timing belt replacement, a chain replacement is necessary. And then compare the costs.

Quote:

Or have you ever seen a timing belt in a critical location on an aircraft engine?

Yes, I have.

Quote:

"What I experience through my five senses is enough for me. And you rarely hear about complete chain failures, unlike TDI timing belts (especially those connected to the water pump)."

Then you'll feel bad about yourself.
For example, VW has had a higher percentage of engine failures caused by defective timing chains compared to failures related to the timing belt. Many people don't want to hear this, but it's true.
In absolute numbers, the occurrence is negligible. However, since the TDI engine is one of the most commonly produced engines in Germany, you also hear a lot about failures. But if you calculate the number of failures based on the total number of engines sold, it's not actually that much.

That would be the same as claiming that the Boeing 747 is an unsafe aircraft. Many of them have "gone down." A Concorde has only crashed once. Therefore, the aircraft is much safer. However, it's important to consider that the one incident represents 5% of the total number of Concordes.
Which airplane is safer?

Quote:

If you're looking for something that requires regular oil and filter changes, inspections, and tightening, then no, it's not maintenance-free.

Unfortunately, simply tightening it isn't always enough (see Rogers' post).

Quote:

I would like to disagree with that, assuming the prescribed maintenance intervals are followed.

If you've ever changed a chain and had it fly off shortly after the change, you'll have a different perspective on the matter. Every motorcyclist can probably relate to that experience.
Or do you also consider the Harley's belt drive system to be a design flaw? Ask Harley riders about ZR (Zahnriemen) failures, and while you're at it, ask Yoghurtbecherfahrers (presumably referring to riders of small, possibly scooter-like vehicles) about chain breakage.

Quote:

... I haven't mentioned anything about the "pre-chamber" combustion process, which is only indirectly related to the valve control system.

Because you're not considering the stresses that occur in modern HD diesel engines. The two concepts are simply not comparable.

Quote:

Perhaps you misunderstood my example with the timing chain, thinking that I consider it the ultimate solution and the best way to go. However, that is not the case. Rather, I criticized the timing belt drive in such a critical area. What bothers me is that many technically sound TDI engines have to fail prematurely because the priorities in the design shifted from "longevity and reliability" towards "low manufacturing cost," "low operating noise," and "weight reduction."

The ZR drive has been used by FIAT since the early 1970s. No one at FIAT has ever complained about it. VW has been using the ZR drive since the first Golf (1974).
Just because the HD Diesel systems misjudged the stresses and people didn't believe the claims made by the manufacturers of these systems, now they are attacking the ZR.
The ZR has enjoyed a trouble-free (maintenance-free) life for over 25 years.
By the way, the mileage on my DX is 250,000 km and it's 26 years old. That says a lot about its durability.

Quote:

My reservations can actually be reduced to two basic problems: 1.) Minimize the residual risk of a total loss. So-called "free-running" engines for gasoline engines meet this condition, as a collision between an open valve and the piston is not possible due to the design. 2.) Avoid high maintenance costs/high effort. This problem is only partially solved by free-running belts (which are only common in gasoline engines), as the belt can be driven until its natural end, but then a potential failure must be accepted. Solutions here involve more complex designs such as a properly sized chain, spur gears, a lower-mounted crankshaft, pushrods, bevel gears, a constant-velocity joint, or electro-hydraulic valves.

Free runner?
That's already impossible with modern gasoline engines, especially with the 4-valve engines that are commonly used today. A free-running valve system is only possible with 2-valve (standard gasoline) engines and with valves that are arranged in a specific way. This is not the case with the engines that are predominantly manufactured today.
It's simply impossible due to the design of a diesel engine.

Quote:

By the way, I dare to claim that, ultimately, a maintenance-free solution (in the sense of "no machine component needs to be replaced") would be economically worthwhile for the average end consumer. If you sum up the costs of replacing timing belts over the lifetime of the product, you have a margin of less than €1500, which would be enough to install gold-plated drive gears from the factory .

However, this cannot be used to operate HD diesel engines. The required injection pressures can no longer be achieved with 100% rigid systems, and even with variable geometry components, there are inherent limitations (see ZMS + T5 PD).

Quote:

However, as I said, the market and company policies/sales strategies prioritize other things. The fact that they learned from mistakes with the new T5 TDI-PD and are also catering to commercial customers proves that VAG is very much aware of the problems.

However, the chain-driven system has a lot of problems, so it probably won't be around for very long.