Engine Stalling: Is It Bad for Your Car?

Hello,

On my daily commute home, shortly after leaving work, I have to cycle up a moderately steep hill for about 2 kilometers (it's a winding, narrow forest road).
My tractor can maintain a speed of 50-60 km/h in 5th gear without any issues. It could go faster, of course (as the turbocharger pressure increases with every km/h at around 1200 rpm), but it's not entirely safe due to the rather unclear and winding road.
Below 50 km/h, the car loses power in 5th gear due to a lack of boost pressure.

Now, one might think "", but I (so far) associate that more with high load at low oil pressure:
If I were to drive the track with the engine already hot, the pressure might reach 1.5 bar – then I would be worried that the very thin oil would be forced out of the bearings, while the supply would be somewhat limited due to the lower pressure.

With a cold engine, my Conrad metal detector shows around 5 to 6 bar of pressure on that particular forest trail (depending on the season), which means that at higher engine speeds, it would hardly be possible to build up any more oil pressure (maximum: approximately 7 bar).
Therefore, I believe that the "honey film" in the bearings of the crank mechanism is more likely to be (slightly) torn by higher rotational speeds than to be squeezed out of the bearings by high operating pressures.

What do you think: Would driving uphill in the cold, in the 4th gear at around 1500 rpm, with slightly less load and only a slightly higher oil pressure, be gentler on the engine?

If I were to drive the track with the engine already hot, the pressure might reach 1.5 bar – then I would be worried that the very thin oil would be forced out of the bearings, while the supply would be somewhat insufficient due to the lower pressure.


Hi Ulf, it's certainly not easy to engage in a discussion with you , but: I think the supply is secured because the oil is thinner when it's warm, and therefore much less pressure is needed to properly lubricate all the relevant parts with oil. My thoughts are more focused on diesel consumption.
If you can trust the MFA (Multi-Function Display), it can be more economical to shift down a gear under certain load conditions. The engine consumes significantly less fuel (sometimes up to 1 liter) even though it is...
all drive-related components must be moved faster.


With a cold engine, my Conrad metal detector shows around 5 to 6 bar of pressure on that particular forest trail (depending on the season), which means that at higher engine speeds, it would hardly be possible to build up any more oil pressure (maximum: approximately 7 bar).
Therefore, I think that the 'honey film' in the bearings of the crank mechanism might be more likely (to some extent) to be torn by higher rotational speeds, rather than being squeezed out of the bearings by high operating pressures.

The thoughts regarding oil film rupture are certainly not without their complexities... (I don't have a well-founded idea about it). What about the other side of the coin, namely the high operating pressures and the resulting faster heating of the cylinders?
What does the ZKD say if the engine's warm-up phase occurs in such an uneven manner?
As mentioned before, diesel consumption in the 4th gear at 1500 RPM might be lower than in the 5th gear at 1200 RPM.

Marco wrote:

I believe the supply is secured because the oil is thinner when warm, and therefore, it doesn't require nearly as much pressure to properly lubricate all the relevant parts.

Hi Marko,

Sure, hot oil flows better and therefore doesn't build up as much pressure. However, it also gets pushed out of the bearings more quickly.
If I drive with a hot engine at a low RPM, for example, at 1.5 bar instead of 3 bar in a lower gear, I am "wasting" 50% of the potential oil pressure.
With a cold engine and 5 bar instead of the maximum 7 bar, I'm only wasting 29%, but I'm avoiding "unnecessarily high" RPMs, which a cold engine doesn't particularly like – and this is, as far as I know, mainly due to the aforementioned thick oil.

Quote:

What about the other side, concerning the high working pressures and the resulting faster heating of the cylinders? What does the ZKD say if the engine's warm-up phase occurs in such an uneven manner?

Hmm, the power output of the engine is essentially the same.
In 5th gear, you'll experience "hot" misfires with larger intervals between them, while in lower gears, you'll experience fewer "hot" misfires occurring in quicker succession.
At least, from a superficial and theoretical perspective, this should balance out, so that the rate of warming should actually be the same. . .

Quote:

As mentioned before, diesel consumption in the 4th gear at 1500 rpm may be lower than in the 5th gear at 1200 rpm

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The different power losses could, of course, cause the motor to heat up at different rates. This could be clarified using an "efficiency scallop diagram" (unfortunately, I don't have one available).
An alternative would be a fuel gauge, but my minimalist tractor doesn't even have one...

I can share a practical test with you.
My wife drives a heavy A4 with an AJM engine. It has been chipped to produce 400 Nm of torque. After about 500 meters of driving in the morning, the road becomes quite steep (approximately 8%) as it goes uphill. Although I repeatedly warn her about the potential harmful effects of high power output on a cold engine, she never manages to stay behind the slower vehicles and always overtakes them. A slight vibration, common in chipped TDI engines around 2,000 RPM, often occurs, which I see as an indicator of the increased torque. This means she's achieving more Nm than would be possible with a standard engine! However, this happens at engine speeds up to a maximum of 2,500 RPM.

Personally, it gives me goosebumps. However, she's been driving it well so far with that style. The car has 75,000 km (approximately 47,000 miles), with a chip installed for 65,000 km (approximately 40,000 miles), and shows no visible wear or defects.

I also imagine all the people who drive similar distances and don't worry about their engines. If our engines were sensitive to such mistreatment, there would be a lot more damage. Blown head gaskets are more often a result of other cooling problems, such as a lack of water. I'm just thinking about Rainer's A3 right now...

I've often wondered if my cautious way of warming up the engine might be counterproductive. It takes considerably longer for the engine to reach its operating temperature. My wife, on the other hand, experiences a much shorter period of harmful cold running.

The oil supply should not be an issue with our current engines and oil types, regardless of whether the oil is honey-thick or water-thin. The engines are designed to withstand any kind of abuse without damage.

Best regards,
Uwe

Hello everyone.

Hello Ulf,

"So, I also warm up my TDI engine in the lower RPM range, just like you. However, I've often wondered how good or bad that is for it. Yesterday evening, I drove (for those who know the area) from Olpe towards Cologne on the A4 highway, covering 22 kilometers. At the beginning, it's slightly uphill, then it's mostly downhill for a long stretch. When I arrived at my destination, I didn't exceed 80 km/h (I had plenty of time) and was always in 6th gear. The temperature was still quite a bit below normal (outside temperature was -5.5°C). That's when I started wondering if it was worth it. (Sometimes I'm a bit strange and I think: 'Turn on the heater only when the engine is comfortable')."


To put it simply: I have a question for you. As you may have seen back in the day, people often used cardboard to shield the radiator. I now regularly drive the route I described earlier, and I'm wondering if there's anything that could be better insulated there. I know that the cooling system only activates the radiator at a certain temperature, but at those temperatures, I notice that my warm TDI, without gas, consistently cools down as it goes down the hill.

--maybe a silly objection--

matthias

I can at least provide some information about fuel consumption. I once tested our G4 variants with the 100PS TDI engine to see how much fuel they consumed at 50 km/h in 4th and 5th gear.
The result was that on a relatively flat road where you can maintain a constant speed of 50 km/h, the fuel consumption was slightly lower in 5th gear, about 0.5 liters according to the MFA (Multi Function Display). However, as soon as a curve appears and you need to steer, the value increases again. Even a slight incline in the road causes the fuel consumption in 5th gear to increase rapidly, by almost 2 liters, compared to 4th gear. This makes sense because the engine has to exert "more" force at the higher gear ratio to keep the car moving, which means I'm essentially giving it more gas in 5th gear. This is noticeable even on very slight inclines.
The disadvantage is that you don't really notice it as much in a diesel engine because of the relatively high torque. In a naturally aspirated gasoline engine, the fuel savings in the fifth gear were much higher in town, but you also tended to downshift voluntarily when going uphill.

Generally speaking, as long as the engine doesn't sputter when you're driving up a hill at 50 km/h in 5th gear, it shouldn't cause any damage. Unless the oil pressure is too low, which could mean that some parts aren't being lubricated properly.

Regarding cardboard:
The radiator on my 1Z has something like gills on one side that seem to fold back and allow air to flow to the radiator only when there's a certain amount of airflow.

Hmm, I've noticed that my AJM engine is most fuel-efficient when I accelerate quickly (always between 1900-2400 RPM) and then quickly shift into 6th gear and maintain that speed.
This driving style (without engaging the turbocharger) is not fun for me anyway...
It actually gets me to a speed that is even 10 km/h faster, and allows me to coast in 6th gear for a slightly longer time without pressing the accelerator...

I would definitely prefer to use the 4th gear instead of the 5th gear when driving uphill!

...or you can shift into the highest gear and go a little faster...

Best regards,
Uwe

matthiasTDI96 wrote:

Back in the day, you often saw people driving around with cardboard in front of the radiator. I now always drive the route described above and wonder if there's anything that could be better insulated there. I know that the cooling system only activates the radiator at a certain temperature, but at these temperatures, I notice that my warm TDI, without gas, consistently drops in temperature as it goes down the hill. --maybe a silly objection----

Hi Matthias,

IMO, that's not a bad point at all. If you could easily install those cardboard pieces (like you could with my previous Peugeot 205), I would even drive that thing around during the colder months.

"In my opinion, this should definitely have some effect, even below the thermostat's opening temperature. Because without the cardboard, constantly "cold" air flows onto the engine block and immediately draws the small amount of waste heat out of the engine compartment."

Using cardboard would reduce airflow, which means the engine could reach its operating temperature more easily.
You won't be able to achieve a completely airtight seal with just one piece of cardboard anyway, so there will probably still be enough air circulation to prevent the engine from overheating (if the thermostat is open).

And if the temperature happens to rise unexpectedly, you can simply turn the heating up full blast (which is possible in winter / then the TDI will also get really warm ), and drive with a slightly lower load, and the engine will quickly cool down to normal temperatures again.

But, as I said, I wouldn't know how or where to insert a piece of cardboard into the G3 (or also the Ibiza 6K) without having to disassemble the entire front of the car .

I don't think it's very useful. There's already a draft in the engine compartment, and you'll never be able to seal it completely. And the small amount of air that you block with the cardboard won't make a significant difference. The cooling effect on the engine block would be negligible.
The flap on the radiator has a different function: if the fan is running while the vehicle is stationary, without the flap, a pressure equalization would occur on the side of the fan. The heated air drawn through the radiator would then flow back past the fan and re-enter the radiator, creating a continuous cycle. This constant heating of the cooling air would significantly reduce the cooling efficiency. While driving, the airflow simply pushes the flap open, making the full surface area of the radiator available.

Best regards,
Uwe

ja sicher ist klar das es da zu Problemen kommt, wenn da ein Stück "Pappe" oder irgendetwas anders hin sollte. Habe mir das gerade mal bei meinem Golf IV angesehen, da ist auch kein rankommen. Ich dachte halt nur.... was mich nämlich so ungemein stört ist das schon beschriebene Problem: Wir haben hier im Sauerland Berge, nicht die höchsen dafür allerdings fast nichts gerades. FOlgendes Passiert jeden Tag. Ich fahre langsam und gemühtlich meines Weges ( mal ehrlich auf es ist doch wirklich eine große Überwindung einen TDI so richtig sparsam zu fahren ) ( ach jetzt nicht denken ich fahr nie über 60, dann hätte ich mir keinen mit 130PS gegönnt ) und es wird nicht warm, habe ich es dann etwas wärmer, rolle ich wieder einen Berg herunter. Daher kühlt er sich durch den Fahrtwind und das was durch die heitzung geht wieder ab. Wie ihr in meinem ersten Bericht gelesen habt, geht das Spiel bei -5°C und weniger locker 20Km lang. ich denke nur daran das das auch für den Motor nicht gut ist. Häufig bleibt die Heitzung auch aus, das ist aber auch keine Lösung. So It struck me as a "cardboard idea."

Matthias.

Yes, when going downhill and the slope is steep enough, your engine consumes absolutely no fuel. Therefore, no heat is generated, except for the frictional heat within the engine. When going uphill, the engine has such a high efficiency that only just enough waste heat remains to power the heating system. The coolant is not heated enough to be able to release heat during the downhill phase. Placing cardboard in front of the radiator doesn't change anything. The problem isn't that the engine is being cooled too much, but rather that it generates too little waste heat overall.
I once touched the radiator after driving 20 km in winter, and it was still ice cold!
I think the only solutions for this problem are an external auxiliary heater or a garage.

Best regards,
Uwe

Hello,

Quote:

Going downhill, no heat is generated either, except for the frictional heat in the engine.

That's not correct. During each compression stroke, the air in the cylinder is heated up to 800 K, even without fuel injection. Otherwise, the diesel wouldn't ignite spontaneously.

Cardboard placed between the climate control condenser and the water cooler fits perfectly.

@ulf
A hydrodynamic lubricating film is not primarily formed by the pressure of the fluid, but rather by the rotational (or general) movement between the parts.
The feeding section is even designed in areas where the pressure is the lowest.

I think it's irrelevant for modern engines, but based on my gut feeling, I would probably choose the 4th option in your example.

Best regards,
Albrecht.

Albrecht wrote:

That is not correct. During each compression stroke, the air in the cylinder is heated by up to 800 K, even without injection. Otherwise, the diesel would not ignite spontaneously.

During the subsequent relaxation phase, the cylinder filling will cool down to its initial temperature.

Best regards,
Uwe

Albrecht wrote:

A hydrodynamic lubricating film is not primarily formed by the pressure of the fluid, but rather by the rotational (or general) movement between the parts. The feeding section is even designed in areas where the pressure is the lowest.

Okay. The maximum pressure is much higher than the 1.5 or 6 bar that are typically measured. The static oil pressure only needs to be high enough to ensure that the required amount of oil, which is drawn into the bearing clearance, is readily available.
I would rather view the wear and tear problem in a more general way:
The normal operating condition is when the system is warm. All clearances have adjusted during the initial running-in period, to the extent that this is still necessary or possible given today's tight tolerances. Due to the uneven thermal expansion of all components (despite the use of temperature-compensating pistons), this adjustment may be slightly disrupted in the cold state, so that areas that currently protrude slightly may experience slightly increased wear.
It's likely that gasoline engines will suffer the most, as the gasoline can condense on the cold cylinder walls and wash away the oil film.

Uwe wrote:

That is not correct. During each compression stroke, the air in the cylinder is heated up to 800 K, even without injection. Otherwise, the diesel would not ignite spontaneously. Albrecht wrote: During the subsequent relaxation, the cylinder filling cools down again to the initial temperature! Both statements are correct, and as long as the air is hotter than the engine block, it will transfer heat to the latter. Although it's only for fractions of a second, but still... the air pump also gets warm continuously when inflating a bicycle tire

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