TDI: Can You Drive at Low RPM?

Hello specialists,

I recently bought a Polo TDI with a 1.9L diesel engine. Since I also like to drive economically, the question arises: can these engines even handle low RPMs (around 1200-1500) under (light) load?

A mechanic once told me that engines with plain bearings should not be operated at low RPMs, as this can result in insufficient oil pressure reaching the bearings, leading to premature wear. However, modern PD engines can already develop significant torque in this low RPM range.

So, is it harmful to drive around the city at 1200 RPM?

Hello Kai,

As long as it's not driven at full throttle with 1200 rpm every day, it's not a problem.

Best regards, Rainer.

HI,

"I've been doing this for 100,000 kilometers in city traffic, and usually even lower (1000 RPM). As long as you don't, as Rainer already mentioned, consistently apply full throttle in that range for extended periods (which is difficult anyway, because you quickly exit that range unless you're stuck behind a slow vehicle or going uphill), it's perfectly durable."

Best regards,

Jan.

As long as the engine doesn't "protest," I wouldn't worry.

You can, for example with mine, easily glide even at 1000 RPM, but if you accelerate, it becomes uncomfortable => downshift, accelerate, upshift .

With my previous car (Suzuki Ignis 1.25 DDIS, also known as 1.3 CDTI or 1.3 JTD), I also tended to drive at low RPMs. The 16-valve engine allowed this without complaint, and the very short gearbox also supported this low-RPM driving style. You could drive it in the city at 50-60 km/h in 5th gear with the tachometer needle below 1500 RPM. 85 km/h corresponded to 2000 RPM. 2500 RPM was equivalent to 105 km/h. The 1.3 DDIS engine ran very smoothly and vibration-free with very little throttle from 1200 RPM.

Charakterlich bin ich ihn eher wie einen Saugdiesel gefahren und habe spuerbare Turbounterstuetzung nur zum Ueberholen oder staerkeren Beschleunigen genutzt.

The tuning was a mess: At first, nothing happened, and then, at 1750 RPM, the thing suddenly ripped through the gears. It was poorly tuned and more annoying than useful in everyday operation. I really don't like tunings like that. So, I drove in a way that minimized the risk of that sudden surge of power. Besides, I'm not the type to "push" the engine; I tend to drive more defensively.

The current Peugeot 206 with the 1.4 HDI engine is tuned in a rather unremarkable way. Despite the relatively high turbo boost pressure (for such a small engine), the power delivery is smooth, and the turbo support kicks in earlier and, above all, more gently. Apart from the different engine speed, the small HDI feels like a gasoline engine. The relatively long gear ratio takes some getting used to, and the engine doesn't run smoothly or quietly, either when warm or cold, below 1500 rpm. It prefers a slightly higher, free-revving speed with more RPM but less boost. However, the higher RPM ultimately results in lower fuel consumption compared to the forced low-rev driving, which the engine only tolerates within a very narrow RPM range anyway.

You don't need to shift into 4th gear below 55 km/h, and the 5th gear isn't really useful until around 85 km/h without any engine noise. The benefit of the long gearbox is incredibly low fuel consumption, especially at highway speeds of up to about 140 km/h, combined with a pleasantly low noise level. The downside is that you're constantly forced to shift gears in town and on country roads, whereas with the Suzuki, almost everything could be done in 5th gear, as long as you didn't need to stop or overtake.

Here's a bit more about the oil consumption: The Fiat engine in the Suzuki always consumed oil. This was the case when it was new, in its early stages, and even with over 80,000 km on the odometer. Initially, it consumed a lot of oil - the first oil change was necessary after only 1500 km, despite a conservative driving style. Oil changes were performed under warranty, and after 7500 km, the oil was gone again, requiring another warranty replacement. Subsequently, the oil consumption remained at a level of 1.5 to 2.5 liters between oil changes, which is equivalent to 15,000 km. Longer and faster highway drives, or even short bursts of full acceleration, would further increase the consumption. However, I never reached the 1 liter per 1000 km that the manufacturer considered "normal." Many Opel Corsa C drivers reported the same, and they often had even higher oil consumption than I did. Some drivers reported that a full oil change could be used up in as little as 300 to 400 km of highway driving with a high percentage of full acceleration.

Unlike the 1.3 CDTI, I've noticed that the 1.4 HDI has less (visible) smoke. The Fiat diesel engines also produce a significant amount of smoke even without being tuned. And those who then increase the fuel rail pressure with piggyback modules really turn them into smoke machines.

The 1.4 HDI engine originally doesn't have a DPF - mine has been retrofitted with an open system. In my opinion, it didn't need one, because I've never seen so little soot coming out of the exhaust pipe with this engine. My Suzuki was always heavily coated with soot, and the rear of the car got dirty very quickly. With other Peugeot models with the 1.4 HDI engine, you don't see any of this. No visible soot and no black rear ends. And most of them are likely without a filter.

Old topic, I know...

But aren't the engines actually designed in such a way that they only deliver a certain amount of power at very low RPMs to prevent them from damaging themselves? Or does this only apply to more modern engines?

Martininii wrote:

Old topic, I know.... But aren't the engines actually designed in such a way that they only deliver a certain amount of power at very low RPMs to prevent them from damaging themselves? Or does this only apply to more modern engines?

Hello,

In its standard configuration, the motor's torque should be designed in such a way that it won't break.
However, it makes sense to downshift, at the very least when the engine starts to drone or sputter.

Interesting fact: The CFFB engine in my wife's A3 can easily be driven at 1200 rpm, and at that speed, it actually has a lower fuel consumption than at 1500 rpm in a lower gear.
The CXHA engine in the T6 cannot be run at very low RPM, and its optimal fuel consumption is around 1400 RPM. This means that sometimes you can even save fuel by downshifting.
You see, there isn't really such a thing as a universally valid statement.

Best regards, Rainer.