How to drive fuel-efficiently. (Solution)

Hi everyone,

no, this time it's not about the diesel engine problems of my 1988 Orion , but rather a more general question:

The car is extremely sluggish (40 kW and no more power to spare), so every time I accelerate (what an understatement), I wonder how to drive fuel-efficiently without becoming an obstacle to traffic.

Should I floor it and shift early, or should I turn off the engine and avoid speeding?

Happy is he who is not in this predicament!

Regards,
Anton.

PS: Is there a difference in how to drive most fuel-efficiently between gasoline and diesel engines?

anton wrote:

Do I give it full throttle and shift up early - or do I turn off the engine and thus avoid being a leadfoot?

Hi Anton,

Based on the principle that engine efficiency is generally best at high load, I would instinctively choose the first option.
(As far as I know, this is even more true for gasoline engines than for diesel engines.)

Furthermore, this allows you to achieve the lowest possible engine revolutions per distance traveled, thereby saving the corresponding amount of energy due to the reduced number of revolutions.
If you don't understand what I mean: Manually rotate your engine (with the glow plugs removed) one full revolution. This "amount of force" is what you save with each revolution less in the highest possible gear, using diesel fuel.

The knowledgeable car enthusiasts (ErnstS and Co.) can probably explain this better - or disprove me, and if they do, that's fine, I can handle it.

Thank you for the tip!

Okay then: PEDAL TO THE METAL!!!

Regards,
Anton.

PS: My consolation: It doesn't matter WHAT you drive, but HOW!
Or, as the English say: It's not the meat, it's the motion!

[quote="ulf"]

anton wrote:

The knowledgeable car enthusiasts (ErnstS and Co.) can probably explain this better - or disprove me, and if they do, that's fine, I can handle it. 8) :D

There's nothing to refute. Here's the translation:

"The effect is particularly pronounced in gasoline engines because the engine power is quantitatively controlled, meaning it's regulated through throttling."
For diesel engines, this is mostly not the case, but the older /8 models did have a throttle valve - which was definitely necessary to control the excessive power output...
However, under high load AND high speed, the efficiency drops even further because the diesel engine requires a relatively long time for fuel injection and combustion. This available time decreases as the speed increases, which further deviates the engine from the thermodynamic ideal, which involves energy input at a constant volume (isochoric).
However, this effect is not as significant in a normally designed engine as the throttling losses in a gasoline engine.
A high load doesn't necessarily mean flooring the accelerator just above idle speed; the engine needs to reach a sufficiently high RPM to actually provide power.

aaaach, following a truck in its slipstream really works wonders 4.7 liters of fuel consumption with my Passat 1Z station wagon with roof rails and Lassafieber winter tires (that's the worst) with some city driving (around 30%) However, I shift up very early (max. 1500 rpm per gear)

Who offers a lower ?

Best regards, Christian.

haehnlein wrote:

4.7 liters fuel consumption with my Passat 1Z station wagon with roof rails and Lassafieber winter tires (that last piece of junk) with some city driving (around 30%) However, I shift up very early (max. 1500 rpm per gear) Who offers less

?

Hi Christian,

4.0 - max 4.5 liters (with summer tires with high rolling resistance ) in mixed town/country road driving.

Fuel consumption slightly higher, up to about 5 liters (average speed 120-130 km/h, with occasional bursts of full throttle to clear the exhaust).
However, all without roof rails.

Drafting behind trucks is too slow for me; I prefer to overtake. The acceleration from a standstill is particularly impressive on country roads in 4th gear. Gang fun

I probably shift gears the same way you do, and only use the brakes in exceptional cases --> letting the car roll to a stop early is "my trick."

@ulf,

You should consider entering the Volkswagen competition for the most fuel-efficient driver.


'I might not be able to match those fuel efficiency numbers, but I also tend to drive my 1Z quite aggressively. I drive about 120km (round trip) to work every day. The route consists of country roads, highway (around 150 km/h), and some smaller city sections. With winter tires (Fulda Kristall Gravito), I use about 5.2 liters, and in the summer (Firestone Firehawk 7xx), I use about 5.1 liters. But, as I said, I'm not driving in a fuel-efficient way, with the engine working constantly. I shift gears, like you probably do, around 1500-1700 RPM.'

Deleted as requested.

ulf wrote:

I probably shift gears in the same way as you do, and only use the brakes in exceptional cases --> letting the car roll out early is "my trick"

Hi Ulf,

.....accurate and idle/thrust cutoff The AFN seems to be more fuel-efficient than the 1Z... I believe, according to tests, it uses half a liter less .

Your consumption is not yet record-breaking ... if I remember correctly, a certain Audi 100 TDI managed over 4000 km on a single tank (80 liters) . This is somewhere in a Guinness Book of Records: average consumption of around 1.7 liters at an average speed of 60 km/h (I don't remember the exact number anymore... please correct me ).

Best regards, Christian.

joergs wrote:

approximately 5.2 liters, and in the summer (Firestone Firehawk 7xx), approximately 5.1 liters.

Hi Jörg,

it's okay........I'm just cruising in the slipstream of the truck and only using 10% less fuel.......hmm....either mine is using too much or yours is using too little .

Best regards, Christian.

Hello DieselGustav,

No, I have the sluggish, slow-moving car with a 1.6 cc engine and 54 horsepower (more like ponies, really).

To save fuel and improve performance, I've already replaced my spare tire with a tire repair kit – to reduce weight! No joke, I got this from a brochure published by the German Federal Ministry for the Environment.
But I would certainly appreciate any further tips.

What I've found out so far: It's a Bosch distributor-type electronic spark advance (ESP), which is more robust than Lucas systems, but unfortunately nowhere near as robust as sequential ESPs.
That's why I prefer to use less vegetable oil, especially since this is the second ESP! The first one was probably bad from the beginning; I could only get to the 5th gear. He was struggling to accelerate in the lower gears, and the higher the engine speed, the more difficult it became – which is actually quite paradoxical!
I hope this is the 2nd one. ESP now lasts a little longer .

Regards,
Anton.

PS: My lowest fuel consumption record: 4.4 liters, my highest. Consumption record: 10.3 liters (though with an initially defective and leaky ESP system and full throttle on the highway), average: 5 liters. I'm not brave enough to tailgate other cars because of the police: safety distance!

I, however, shift up very early (max. 1500 rpm per gear) .

Who offers a lower ?

Best regards, Christian

Much too soon...

The TDI engines achieve their best fuel efficiency within the range of 1500-2500 RPM, depending on the load.

Is anyone able to access the fuel consumption data for individual engines?
Unfortunately, I only have 'typical' identification codes for DI engines .

'But drafting and a 4.7L engine? How fast is the truck?'
at 80 WITHOUT slipstreaming, my automatic mill consumes 4.2 - 4.5 liters on a straight road. When I get stuck in traffic behind a truck, I often average 4.4 - 4.8 liters over the entire distance (40 km, of which 15 km is uphill and downhill). With unrestricted driving, it's then 6 .

CU Gremlin.

Gremlin wrote:

far too soon...

Hi Gremlin,

It's a matter of weighing the pros and cons... the few drops of diesel you might save by shifting up "later" can be easily offset by driving slower or coasting. For me, the additional wear and tear on the synchronizers and engine (especially when cold) doesn't justify the fuel savings.

Gremlin wrote:

but drafting and 4.7 liters? How fast is the truck? at 80 WITHOUT slipstream, my automatic mill consumes 4.2 - 4.5 liters on a straight road. When I get stuck in traffic behind a truck, I often average 4.4 - 4.8 liters over the entire distance (40 km, of which 15 km is uphill and downhill). With unrestricted driving, it's then 6

.


Around 90 km/h. My fuel consumption is definitely not optimal: a friend of mine manages to get around 4.0 liters with a similar driving style (A4 TDI 1Z, not a wagon, 240,000 km).

It would be interesting to know what the starting point of the pump's activation needs to be in order to achieve an optimal consumption rate . My pump is currently set a bit too early (between the midline and the upper tolerance line). Since I changed my setting from "very late" to "slightly early," surprisingly, nothing has changed in terms of consumption .

Best regards, Christian.

hi,

To avoid going completely off-topic, shouldn't we start a new thread for that?

Okay, let's not start comparing apples and oranges now? We were talking about the Passat, Golf, and Octavia. After all, there are already fundamental differences: different sizes, which means different weights, and different aerodynamic properties!

@Gremlin:
I own an MTZ article about the TDI engine from 1996. This article includes, among other things, a fuel consumption chart for the 66kW TDI engine with a wastegate turbocharger. It should be the engine with the MKB AGR code, but I'm not 100% sure.
Based on this shell diagram, it can be confirmed that the TDI engine achieves the best specific fuel consumption in the speed range of approximately 1500-2100 rpm and under very high load (12-14 bar of effective mean pressure!!), with a value of approximately 198 g/kWh in this range.
With a slightly reduced engine load (8.5-13 bar of effective mean pressure), the engine still achieves a specific [performance metric] within the speed range of approximately 1200-2600 rpm. Consumption of approximately 210 g/kWh.
To optimize fuel consumption during a journey, it's generally best to maintain a high engine load while keeping the RPM as low as possible. However, when combining very low RPM with full load, caution is advised, as the load-bearing capacity of the lubricating film in the main bearings of the crankshaft depends on the RPM. This is particularly important when the machine is hot, as the oil viscosity may have decreased significantly.
That's why I never fully load my engine between the low-revving speed and 1500 RPM, but instead, I only depress the accelerator pedal about two-thirds of the way. I only dare to increase the load to 100% above 1500 RPM, for the sake of my engine's longevity.
When driving at a constant speed on a flat surface, you should always use the highest possible gear whenever possible to maximize engine load.
Here's an example: To move the vehicle at a constant speed of, for example, 100 km/h on a flat surface, we need a certain power output from the drive system, let's say 20 kW (this is just a very rough estimate without further calculation). If we drive at this speed in 5th gear, the engine will run at the lowest possible RPM (e.g., approximately 2200 RPM for an A3 with engine code AGR). In 4th gear... The engine's RPM increases noticeably, even though it still needs to provide the same amount of power to overcome the driving resistance.
The power in a rotating system is defined as the product of torque and angular velocity, where the angular velocity is proportional to the rotational speed.

P = M * 2 * π * n / 60
(M = Torque [Nm], n = Speed [1/min], P = Power [W])

Referring to our small example, this means that with constant power and a higher speed, the engine torque must necessarily be lower in order for the equation to be satisfied.
Well, lower torque means lower engine load, and that results in a higher specific fuel consumption.

I hope that wasn't too scientifically phrased.

What I actually wanted to say is: For optimal fuel efficiency, it's important to accelerate with a lot of throttle and shift up as high as possible so that you end up at the lower end of the optimal RPM range in the next higher gear.
When coasting, you should choose the highest possible gear and maintain a smooth, consistent speed.
But most importantly, it's crucial to drive with foresight. Because what's the point of optimizing for maximum acceleration if you then lose all that kinetic energy through a completely avoidable braking maneuver, right?!

With my Audi A3, manufactured in December 1996, engine code AGR (66kW, all original, 127,000 km), I achieve fuel consumption values of approximately 4.7 to 4.9 liters per 100 km when driving at a fairly brisk pace on country roads (including hills and valleys!).

Regards,
Alex.

Hi,

I can't imagine that the load on the bearings in the lowest RPM range, at 2/3 throttle, is higher than it is at full throttle. Or do you notice a significant increase in power in the non-turbocharged range? Not with my V6, at least.
It's only when the full boost pressure is achieved that this portion of the accelerator pedal becomes crucial for the engine's performance, and then the stress on the bearings increases significantly, even if the engine speed is only slightly higher and the lubricating film is more robust.
On this occasion: Does anyone have any idea what the horsepower and torque figures would be for the 2.5 V6 engine without a turbocharger? I believe the DB 2.5-liter 4-valve pre-chamber naturally aspirated engine had around 113 horsepower.
Also, there's also a T4 with an 88 horsepower TDI engine and a 2.5-liter displacement (the one with the blue 'I'). Given the liter capacity of the 1.9-SDI engine, it seems likely that the same performance level could have been achieved using an SDI configuration.