Biodiesel Consumption: ESP/ESD Leakage Issues

Increased consumption of RME (biodiesel).

Hello everyone,

I've noticed before that my car consumes more fuel when using biodiesel, or what's often called 'Aldi oil' or rapeseed oil/diesel mixtures, and that the performance also decreases.

The power loss with biodiesel was expected, about a 10% increase in fuel consumption.
However, I had the same experience with PÖL (vegetable oil), which is supposed to have a similar energy content to diesel.
My fuel consumption indicator is quite accurate when running on diesel, with a difference of about 0.2 liters per 100 kilometers.
(Thanks to the logins here on the forum.)

My tests involved approximately 150 liters of a 50% biodiesel/diesel mixture.

Increased consumption according to the display: 14%.
Increased fuel consumption due to biodiesel: 5%.
Increased fuel consumption according to the fuel receipt: 6% (which corresponds to the fuel's energy content).
Difference to display: 8%

Of course, this is subject to potential measurement errors, but for me, it all makes sense together.

The percentage of biodiesel results in increased fuel consumption within the expected range.

The difference between the displayed value and the actual measured consumption is the key issue here.

The leakage current is obviously increasing. Since the on-board computer only calculates the consumption based on the ESP setpoint value, this increase is not detected. This means that the leakage current is increasing by approximately 0.5 liters per 100 kilometers.
Leakage current is the sum of ESP and ESD.

Does anyone know the total amount? (For example, is the leakage current around 5 liters per 100 km for an AFN engine, or something like that?)
Does that allow for a conclusion in the following way:
ESP loading is increasing (a lot / not very much)?

I would like to add that I didn't necessarily expect this, as I had also considered that the larger molecules of the viscous RME or POE might not pass through the gap as easily, which would reduce the leakage current. This would have aligned with the repetitive claims made by some individuals, who insist that RME requires less fuel than diesel (which is not possible).
It's possible that the pressure will increase to such an extent that this effect will occur, but be offset by the increasing pressure.

Opinions? Comments? Experiences? (Workshop bills?)

Hello...

I have driven approximately 70,000 km using biodiesel, and the power loss is normal, even with plant-based oil from Aldi (Hofer).

If a motor has less power, it requires more fuel to achieve approximately the same level of performance.

By the way, biodiesel is still okay, but I would avoid using plant oil.

Best regards, Mike from Austria.

@Mike

I see it completely differently. A diluted oil might occasionally clog a filter, but I'm not going to have to replace the entire ESP system for nearly 900€ just to have it resealed.
'However, biogas is now too expensive to be economically viable in a mixed operation. And converting to a purely biogas-based system is too expensive for me.'

With reduced power output, it doesn't necessarily require more fuel as described above, especially when the power reduction is caused by increased leakage currents. This is particularly noticeable with a sluggish engine ('zäh PÖL'), where you experience significantly less power at the same fuel consumption, but the fuel gauge shows a higher reading - as mentioned before.

70,000 km with RME? Well, maybe you'll be one of the lucky ones who manages to get over 100,000 km out of it before Audi sells you a new pump for €1300.

Deleted upon request.

diesel.gustav wrote:

My long-term observations regarding fuel consumption show: It works reasonably well in the summer. However, even the normal difference in density between summer and winter diesel fuel causes a discrepancy of approximately 0.3 liters per 100 km between the actual fuel consumption measured and the fuel consumption reading displayed in my cars. That also makes some sense: the lower density

is compensated for by a slightly lower injection mass, and I compensate for the resulting lower engine torque by pressing the accelerator pedal a little more. So, by using a little more fuel } to achieve the usual torque. }
Hello Gustav,

However, I can't derive a real explanation for the seasonal discrepancy from that.
If you press the accelerator more (to achieve the usual performance), the EDC "knowingly" injects more fuel, and this extra amount should therefore also be included in the fuel consumption display } }.

Or, for example, is "winter diesel" so much "thinner" that, with the same injection hydraulic pressure, more fuel flows through the nozzles, resulting in an "unnoticed" increase in fuel consumption (which, of course, will not be reflected on the display)?

Hello...

Okay, I can only agree with Ulf's opinion. I experience increased fuel consumption in the winter because I have an auxiliary heater inside, and my MFA (Multi Function Display) doesn't account for that.

Theoretically, 'verbrauch' (consumption) could relate to so many things that one could write entire books about it. For example, using the wrong type of oil, or using thick oil in cold temperatures of -10°C.

I'm having a problem with my Galaxy. It's 7 years old and has 270,000 km (approximately 168,000 miles), and it's using about 9-10 liters of diesel per 100 km (roughly 21-23 mpg). I just can't figure out why. (It's probably due to wear and tear.)


Best regards, Mike.

Hello Gustav,

'I completely understand what you're describing, however, there remains a noticeable 'displayed' increase in fuel consumption when using RME or rapeseed oil, which doesn't appear in the actual measured fuel consumption. When I switch back to diesel, the problem disappears again.'
In short: I've observed that using fuels with higher viscosity leads to a higher fuel consumption reading, which isn't actually the case. I'm trying to figure out the cause. The best explanation I can come up with is leakage.
'According to EDC, more fuel should be injected, but due to the leakage currents, more fuel flows back into the tank than with pure diesel.'

Is this possible or incorrect? If it's incorrect, why is that?

I believe that you have indirectly confirmed my theory, because the difference you described between the viscosity of diesel in summer and winter would support the viscosity theory, wouldn't it?

I don't have a problem with it either; I'm just trying to understand these effects, and if someone proves to me that I'm writing nonsense, then I've learned something new.

'This effect isn't just happening now; I've tried it again because I also observed it last summer, and back then I used about 400 liters of rapeseed oil (mixed with diesel). A few years ago, in my then-girlfriend's TDI, I used about 2000 liters of rapeseed methyl ester until the ESP system failed. The effect is primarily temperature-independent, which makes sense to me, because after just a few kilometers, the ESP and especially the ESD (Engine Speed Sensor) are no longer properly cooled.'
The stronger the effect, the tougher the material being processed. It was the worst with 50% pure rapeseed oil, which I would strongly advise against using.

@Ulf - I think you understood my question.