Winter Driving: Best Practices for Short Trips

Hi everyone, mechanics and those who want to become one.

After being away for eight weeks for training and now having my regular schedule back, it regularly hurts me deeply in the mornings to turn on my ASZ (presumably a piece of equipment), because I know exactly what it's going to be like.

Besides the outdoor temperature of -6°C, which we're all experiencing, especially if we don't have a garage, the daily route now consists of 1 km on flat ground, 3 km downhill, and 2 km in the city.
Not a trace of warmth, understandably.

In the evening, I drove the same route in the opposite direction. Amazingly, due to the city driving speed and the 3 km uphill stretch at 60 km/h, the water temperature gauge suddenly jumped up to 80°C.

That's all for the good ASZ (presumably referring to a specific person or entity) for today.

Now, I'm constantly thinking about the best way to drive this short distance so that the engine and oil aren't too negatively affected by the frequent short trips.

I'd like to hear your opinions on this: Is it better to simply let the engine idle and avoid revving it in the morning, and then drive the route with 2000 RPM in the evening? Or would it be even better to avoid revving the engine at all in the morning? And would keeping the RPMs between, say, 2000 and 2400 be better, as long as the engine isn't under load when going downhill?

Regards,

Calvin.

Calvin wrote:

Now, I'm constantly thinking about how to drive the short distance in the best way so that the engine and the oil are not too negatively affected by the short trips.

My Polo is experiencing something similar, although not quite as extreme.

The whole thing is, in my opinion, a "Sophie's Choice" -> no matter what you do, it's probably wrong somehow.

I only stay within the speed limit: Right after a cold start, don't exceed 1500 rpm, then gradually increase the speed as the temperature rises (if power is needed).

Most of the time, I let it run at around 1100-1200 rpm because I can't resist using the long 6th gear.

I tap the accelerator pedal at least once a day, even when the temperature gauge is only showing around 70° (then up to a maximum of 3000 rpm).

If it ever stops working, I know that the amount of diesel (in the oil) being forced into the intake passages by the fuel injection pump and turbocharger is sufficient to provide lubrication. . . .

It's best to get a cheap winter car .
Short trips like that are murder on a diesel engine.

So, now seriously: (but without making the topic too dramatic, due to saving fuel and protecting the environment).

- If you use a good quality oil (in terms of age, viscosity, and manufacturer), your engine will feel much better in all conditions.

- If you can avoid using full throttle and high RPMs (above 2000 RPM) for the first few kilometers, the machine will thank you for it.

- When going downhill, it might be better to use gear 'X' and let the car roll down at an engine speed below 2200 RPM, rather than using neutral with the engine idling.

- After a short warm-up phase, you can also increase the speed to up to 2400 RPM in the short term.

- It's best to keep the engine speed below 2500 RPM for the entire journey.

- Perhaps drive a longer distance once a week to 'dry out' the engine and properly charge the battery.

Sure, it's clear that it's not economically sound and might even be worse for the environment, but in the long run, it will be good for your wallet (battery, oil, etc.)!

Please don't be disrespectful if someone has a different opinion.
It's just my recommendation!

Best regards, Georg.

Where in "Aschebersch" are there mountains that offer a 3 km downhill ski run?

Otherwise, pay attention to your MFA (manifold absolute pressure). If higher instantaneous consumption values are displayed, it usually means more heat is being generated. In sliding operation, nothing is being combusted, so the engine's work is reduced to some friction and compression heat, which contributes practically nothing to the heating effect. However, trained thermodynamicists can probably explain this better.

Perhaps some "glow plug heater tuning" might help it switch off later.

I personally find that it warms up relatively quickly, even with the heating on its lowest setting (Climatronic at 18 degrees, fan on the lowest speed), and with the recirculation on, especially in dry weather. After just 3-4 kilometers of city driving, the temperature gauge is already between the 2nd and 3rd mark. Then, after another 3 kilometers on the highway at 120 km/h in 6th gear, the temperature reaches 90 degrees (water temperature). Only then does the heating finally start working for me. Sometimes, the gauge briefly drops back to the first mark, even at highway speeds.

Georg-TDI wrote:

Short distances are a KILLER for a diesel engine.

Hi Georg,

What exactly do you understand by "murder" in this context?

Or, conversely, what problems (for which a diesel engine is not designed) would a gasoline engine not have under the same conditions?

For example, I believe that gasoline engines are even less suitable for short trips than diesel engines, due to the significant oil dilution caused by fuel condensation after a cold start.

... In sliding mode operation, nothing is burned, so the engine work is reduced to some friction and compression heat, which contributes practically nothing to the heating effect. But the studied thermodynamics experts can certainly explain this better.

'I'm not a thermodynamicist, though.'

However, I claim that the engine also gets warmer in idle mode, and that diesel engines do so more than gasoline engines!
(Keywords: throttle valve, compression)

While no diesel fuel is injected, a significant amount is achieved simply through air compression. In addition, there is some friction, but only to a minimal extent.

An air compressor will get hot even without fuel.

Best regards, Georg.

Are there any mountains in 'Aschebersch' that offer a 3 km downhill ski run?

If you live in Haibach and drive down to the city, I can sometimes achieve a fuel consumption of up to 1.9 liters per 100 kilometers when there's not much traffic.

So, I've noticed (and I hope I'm being objective) that the water temperature gauge rises faster when I drive the engine at lower RPMs.
When I drive down that slope in the evening, in 4th gear at approximately 1400 RPM, the temperature gauge rises to almost 90°C.

It doesn't matter how I do it, it always goes down. I never revved it past 2200 RPM anyway... there's no point in doing so when it's cold.

I could imagine that the faster temperature increase might be due to the higher pressure at the cylinder head in that speed range.

The question, again, is whether that's really good for the engine...

Hi Ulf.

I wasn't referring to anything specific related to diesel.
These very short distances are bad for both diesel and gasoline engines.

The problem of fuel dilution is even more pronounced in gasoline engines, which is quite clear.
On the other hand, the comparable gasoline engine (which generates more waste heat) warms up much faster, which somewhat compensates for the oil dilution.
Gasoline evaporates much more easily and quickly than diesel.

However, compared to gasoline engines, diesel engines also have a few construction-related issues related to cold starting.
For example, the compression ratio is lower in gasoline engines, and the combustion process is much 'softer.'

G.G.

Georg-TDI wrote:

Although no diesel is injected,

a significant amount is achieved simply through air compression.
I used to think that too, but let's look at the whole thing from the perspective of total energy (without considering frictional heat!):
If the engine were actually heated by the compression, that energy would have to come from somewhere -> presumably from the air being pumped in.
Do you think that the air coming out of the exhaust pipe would be colder than the air that is sucked in at the front?

Quote:

An air compressor gets hot even without fuel...
. . . but only because the air remains compressed during

Quote:

the process!

However, a diesel engine also has a few construction-related problem areas when it comes to cold starting, compared to a gasoline engine.
For example, the compression ratio in gasoline engines is lower, and the combustion process occurs much more "smoothly" }.
Yes, but to compensate, the diesel engine is also built more robustly (with larger bearing diameters, etc. - I hope so...).

So, I guess I've been stepped on...

Yes, Ulf, you're right again.
If we go into detail, then everything you're saying is correct.

I will not now calculate the energy balance of a 4-stroke engine (I couldn't do that right now anyway ).
However, I still believe that the exhaust temperature doesn't represent the complete amount of energy you put in during the gliding phase.
There should still be quite a bit of residual heat remaining in the engine, right?

The air compressor, however, is not exposed to extremely cold airflow, does not have any extremely cold coolant to heat up, and does not have to dissipate its waste heat through a heat exchanger to prevent anything important from freezing for the driver...

And then, the heated air is decompressed in the diesel engine, where, in my opinion, a significant portion of the compression heat is lost, while the compressor works against the pressure in the storage tank, where the air is decompressed to a lesser extent.

Ulf has already written something similar in the meantime, as I couldn't access the forum at that time.
The energy that propels the vehicle downhill comes solely from the potential energy (P pot) of the vehicle, which was initially stored when it was brought up the hill using energy.

Hello,
For this short and unfavorable route, one should consider a parking heater; however, this would only be feasible with periodic recharging of the battery!
Best regards,
Günther.

Tatatataaaaa ...

Welcome, Günther!

Georg-TDI wrote:

So, I guess I've been run over... Yes, Ulf, you're right again. If we go into detail, then everything you say is correct.

Hi Georg,

It's not really about getting knocked out (I'm often on the ground anyway ).

Quote:

However, I still believe that the exhaust temperature doesn't represent the complete energy that you put in during the sliding operation. There should still be quite a bit of heat remaining in the ZK as residual heat, right?

Yes, as soon as one takes friction into realistic consideration.

However, the fact that the compression heat is not stored in the engine can be quite convincingly "demonstrated" by the simple thought experiment described above (no colder air at the exhaust than at the intake).

(I also have a hard time accepting the idea that air, with a temperature difference of a few hundred Kelvin, doesn't transfer any energy to the engine.)

Hello Ulf,
The engine will inevitably absorb some heat from the compressed, hot air during the compression stroke; however, during the expansion stroke, it will also lose heat to the now-cooling air.
Let's not consider minor nonlinearities for now.
Otherwise, the engine would operate as a 'heat pump' in gliding mode.
Best regards,
Günther.

Tatatataaaaa ...

Welcome, Günther!

Hello Roger,
Thank you for the 'reception' here .
Best regards, Günther