TDI Engine: Not Fuel-Efficient Under Heavy Load?

Hi, I wanted to ask what the experts have to say about this topic. I often read these 'diesel vs. gasoline' threads in various forums, where TDIs are sometimes criticized for having a narrow rev range, etc. What I'd like to know is whether it's really worse for a diesel engine to occasionally shift gears at higher RPMs (not always full throttle, but not always shifting at 2500 RPM or so). It's often claimed that diesels only have power in the low rev range and don't need high RPMs, which is true to some extent, but you can also rev a TDI engine a bit more, and it will still be faster than if you shift up to the next gear. However, it's supposedly very bad for a diesel engine to drive it like that, and if you want to do that, you should get a gasoline engine that is designed for higher RPMs. Is it really harmful to drive a diesel engine in this way? I mean, I'm getting a powerful diesel not just to save money, but also to have fun. By the way, I have a 2.0 TDI, but I'm not referring to any specific TDI model.

Best regards,

It seems you don't quite understand how a diesel engine works. These engines don't rev as high as gasoline engines for a reason. Have you noticed that they tend to be tougher at higher RPMs? Why shouldn't they be able to handle high RPMs? Name one TDI that isn't capable of handling high RPMs! These engines are full of electronics, which prevents them from being over-revved. Besides, even the 2.0L TDI doesn't really save fuel if you shift at 2500 RPM. And pushing the engine to its redline doesn't benefit it in any way. Take a look at the torque curve of a gasoline engine and one of a diesel engine. Maybe that will help. Otherwise, have fun reading on the "Gasoline vs. Diesel" forum.

My suggestion is to get a Honda Integra Type R or a Mazda RX8 for enjoying high engine revs in a car. Alternatively, you could consider a modern 600cc motorcycle, where you can really let the crankshaft spin freely.

I understand the principle of diesel engines very well, but I don't believe what you mean with that post. Even if the TDIs become a bit more sluggish at higher RPMs (the 2.0 isn't particularly bad in that regard), I am still faster when I rev the gears up to 3500 or 4000 RPM than when I shift into the next gear; that should be obvious. And why 'If I only shift the 2.0 at 2500 RPM...'? 2500 RPM is not particularly high, even for a diesel engine (if I always drove only up to 2500 RPM, I probably wouldn't need to refuel ), because it still has its full torque at that point. The question is whether it's bad for the TDI to rev it out fully.

Quote:

(not always running at full power, but also not always shifting gears at 2500 RPM or something like that).

The 2500 revolutions probably referred to this sentence, which doesn't really make much sense!

Ultimately, it all comes down to the torque being transferred to the wheels!
And that is logically higher in third gear at 3800 RPM than in fourth gear at 2500 RPM.
(This was just an example, nothing calculated!)

eschmidt wrote:

...It's about whether it's bad for the TDI engine to let it "run down" completely?

Just as bad/good as it is for a similarly "highly-bred" gasoline engine!

Hello Eschmidt.

The reason diesels don't rev very high is that at high speeds, the combustion process starts to lag behind and becomes "unclean" or "irregular." In TDIs, this happens around 4,500 RPM (please don't take that number as definitive), whereas in pre-chamber or swirl chamber diesels, this process occurs approximately 1,500 RPM higher. However, I don't believe that engine speeds of around 5,000 RPM are really harmful to a TDI.
Looking at my ZX-6R, which easily revs up to 14,000 RPM...
The reason why TDIs often feel restricted at higher RPMs is more likely due to the factory engine tuning. It's designed to encourage fuel-efficient driving at lower RPMs. My TDI, which has been chipped, has a completely different characteristic and revs out fully, which is particularly advantageous during overtaking maneuvers.

I hope I've shed some light on the matter.

It's not a contradiction in my opinion that a TDI can accelerate quickly at higher RPMs, as you mentioned. With diesel engines, the maximum torque is achieved very early on, but not the maximum power! My 1Z engine produces its 90 horsepower at 4000 RPM!
With a diesel engine, the increase in power isn't as dramatic as with a gasoline engine because diesels have high torque from the very beginning, which is maintained at a relatively constant level. In contrast, torque and power in a gasoline engine build up gradually with increasing RPM.
So, I would always shift at 2500 RPM; otherwise, I wouldn't be able to overtake quickly, or only after driving for a few kilometers.
I usually drive my car at under 2000 RPM in the city, but when overtaking on country roads, I always rev it up to 4000 RPM – after all, I need to get past.
"Our company's TDIs are constantly running at around 4000 RPM on the highway, and they have now covered 30,000 kilometers. So far, we haven't experienced any problems; they are very reliable."

Hi.

'Full throttle test': Does this mean running the engine at full RPM? All functioning engines should be able to handle that, regardless of the fuel type. However, it does accelerate wear and tear!

Does that mean full load? If so, then it's not at the maximum RPM, but slightly below – see the engine data: maximum power at RPM xxxx. It's always below the maximum RPM.

Für mich ist die Frage : Was passiert bei max. Last.

With a diesel engine, the efficiency drops rapidly as the RPM increases, but otherwise, nothing much happens; the temperatures typically remain within the range that the mechanical components can handle without additional measures.

With gasoline engines, there has always been a full-throttle enrichment setting because it provides a bit more power, but more importantly, it protects the valves from overheating.
Since the introduction of the catalytic converter, not only is approximately 10% more fuel consumed in the partial load range by Lambda 1, but also specifically in the higher performance range that most vehicles reach beyond 130 km/h, and definitely at 160 km/h. At that point, fuel consumption increases again by 10-15% because the catalytic converter, which is now positioned very close to the engine, would otherwise not function properly. The engine then runs with an overly rich mixture, and this operating range is not tested in emissions tests.

To put it simply: All gasoline engines would be running poorly after just a few kilometers of full throttle if you didn't provide them with extra fuel – so they can only handle full throttle with technical modifications.

For those who want to know the exact details: Logging fuel consumption at constant speeds on the highway (120-130 km/h) results in a value of around 170 [presumably liters per 100km or similar], and there's definitely a noticeable jump somewhere along the way.
That's why manufacturers no longer publish consumption curves like they used to, otherwise everyone would notice.

Regarding the RPM range: that's correct; it's narrow for diesel engines. The TDI is better in this regard than other models, BUT:

I can get any TDI, whether it's a 110hp or PD engine, moving in second gear, as long as it's not fully loaded. Otherwise, under full throttle, it will definitely hit the rev limiter in first gear (or the ASR might kick in). In second gear, it goes up to about 100 km/h, and then you can shift into fourth gear and continue accelerating until at least 160 km/h. Which gasoline engine with such good torque can do that with only two gears?

Someone who compares apples to pears will notice that they look and taste different, but that doesn't really help you understand anything more profound.

When I said 'full throttle,' I didn't mean maximum speed, but rather that the engine is revved higher than might be typical for some diesel engines. And I don't mean constantly revving it to 4500 RPM or higher, but more like 3500-4000 RPM, simply utilizing the entire RPM range. That's all I meant, but apparently that's supposedly harmful to a diesel engine in the long run.

Best regards,

Hi,

I wouldn't worry too much about that if I were you; what do you think they do to the engines at the factory before we get them installed and ready to drive in our cars?

I've also tested driving my ARL TDI (150 hp) at very high speeds for several hundred kilometers on the highway... and it works great, especially since it's even been chipped.
I usually drove somewhere between 3800 and 4500 RPM... 1600 km in 2 days... after that, it was really broken in... So, he definitely liked it.

By the way, I also drive it in everyday use at around 2000 RPM, but I also like to shift gears (assuming the engine is properly warmed up), and it willingly goes all the way to the rev limiter... until it slowly starts going over.

Since a proof

http://www.audi-s-racing.de/Images/GolfTDI/24.01.04/DSC04323.jpg

Best regards, Benny.

He's really going wild .
'Yours also has a 6-speed transmission, right? Mine is at just over 220 km/h with the engine running at about 4100 RPM. I also have a 'chip,' a module from KW Systems. Once, I briefly had unrestricted speed, and I was around 230 km/h, but I don't know what the RPM was at that time; it was only for a very short period before I had to ease off the accelerator.'

Best regards,

Hi,

I have a 4Motion model, so the gear ratio is much shorter. On the highway, it becomes a bit annoying above 180 km/h because of the 4Motion system. However, otherwise, it's more enjoyable to drive due to the torque.
But my ARL TDI revs willingly to about 4400 RPM in every gear... if I had a front-wheel drive car, it would have to be really fast .

Best regards, Benny.

eschmidt wrote:

When I said "Vollgasfest," I didn't actually mean maximum speed, but rather that the engine is revved more than might be typical for a diesel in some cases. And I don't mean constantly revving it to 4500 or higher, but more like 3500-4000 RPM, simply utilizing the entire RPM range. That's all I meant, but supposedly that is supposed to be harmful to a diesel engine? In the long run. Sincerely,

Of course, that's harmful. The wear and tear increases significantly with increasing speed and increasing load. This applies to both diesel and gasoline engines. Or do you think a gasoline engine that is constantly running at its maximum RPM doesn't experience this?

'So, my colleague's 1.8T engine ran perfectly well until it was returned (with 132,000 km on the clock), and it definitely wasn't treated gently!'

Now he's driving an ASZ (with approximately 20,000 km on it), and that one is also being treated with the same care. Like a tool, really. His job involves customer service visits, and he needs to get there quickly.

So far, no problems, even with full throttle after a cold start at -10°C .

More often than not, frequent cold starts or prolonged idling are more harmful to engines.
As unbelievable as it may sound, idling is the worst operating condition for the engine.

Consistent full load operation, combined with good and regular maintenance, as well as the proper condition of all auxiliary components, will ensure trouble-free operation.

CU Gremlin.

Yep, those 1.8T engines can really take a beating... And if I have to worry about whether my engine will run at full throttle continuously... well, maybe it shouldn't be an engine in the first place...
Don't misunderstand me, I always warm up my engines very carefully; they never get cold started or anything like that... but once they are warmed up, I drive them accordingly.
I haven't had any engine, turbo, or transmission problems with ANY of my cars so far, whether they were VR6, 1.8T, or TDI models... so I think I'm probably handling them correctly.

I usually drive my car at under 2000 RPM in the city, but when overtaking on country roads, I always rev it up to 4000 RPM – after all, I need to get past.


That's exactly how I do it too. The engine only produces its maximum torque at higher RPMs, and you have to rev it up when overtaking!
So far, nothing has gone wrong with it, considering it has over 300,000 km.

Regards,
Sausage blinkers.