Warm-up phase critical for ZKD?

Hello everyone,

this here

Quote:

If you immediately put a cold engine under heavy load, the cylinder head will heat up much faster than the engine block. . . However, the head gasket will definitely be subjected to very high shear stress because the cylinder head expands significantly more due to the faster heating and the greater coefficient of thermal expansion compared to the engine block. This results in significant shear stress on the gasket within the sealing gap, which is superimposed by the regular stress caused by the internal pressure of the cylinder.

(from /viewtopic.php?t=4896)
It still occupies my mind.

Here are my layman's thoughts on the stress experienced by the cylinder head gasket during the warm-up phase and at the engine's operating temperature.

The different coefficients of thermal expansion for gray cast iron and Al-Si alloys cause the latter to expand more quickly upon heating, and vice versa - see quote.
According to this, the cylinder head gasket is subjected to increasing stress, the warmer (or colder) the entire engine is compared to the temperatures during its assembly - and this already occurs without a temperature difference between the cylinder head and the engine block.

I'm skeptical that the cylinder head grows "twice as fast" as the block during the warm-up phase due to greater heat absorption, because the internal temperature of the cylinder head is practically maintained at the same level as the block by the flowing coolant (thermal equilibrium).

Especially in the combustion chamber, thermal stresses arise internally between the hot surfaces of the combustion chambers and exhaust channels on one hand, and the cooling water and inlet channels on the other.
These variations are mainly dependent on the temperature difference between the combustion chambers and the cooling water. Therefore, they will be most pronounced under "cold full load" conditions and largely disappear when the engine is switched off or during prolonged operation.
The cylinder head is likely to undergo a primarily three-dimensional, "gel-like" deformation (i.e., bending). In particular, the thermal expansion of the material layers on the combustion chamber side will cause them to shift towards the cylinder head gasket and further compress the area around the cylinder bores.

Even with a warmed-up engine, the cylinder head temperatures in the area of the combustion chamber walls will be higher than those around the coolant channels as long as the engine is under load. Therefore, the locally different pressure loads on the cylinder head gasket will decrease compared to cold running, but they will not disappear completely.


My conclusions:

Immediately after a cold start, the cylinder head gasket is primarily subjected to locally varying clamping pressures that depend on the engine load and which decrease somewhat as the engine temperature rises.

2. As soon as the engine warms up, the engine block and cylinder head begin to expand at different rates, which puts additional and increasing shear stress on the cylinder head gasket and increases it progressively.

Since I don't know the actual magnitudes of the aforementioned pressure and shear loads, I can only estimate that the material stress on the cylinder head gasket (as the sum of the mentioned loads) increases with the overall temperature of the engine and is greatest when the engine is hot and operating at its maximum pressure.
-> If someone wants to quickly damage their catalytic converter (ZKD), they should drive with a constant low speed during the hottest part of summer, possibly even very slowly, for example, driving uphill in a caravan (Rainer's experience).

Damage to the cylinder head gasket (ZKD) appears to be a common consequence of coolant loss or water pump failures, which seems to confirm this.


Whoever can refute, supplement, or confirm my preceding thoughts is welcome to type away now .

It would be interesting to have facts about the average combustion chamber temperature (under different load conditions), as one can infer the extent of creep deformation based on that, depending on the instantaneous coolant temperature.
Under prolonged operation with high power output, the engine could actually cool down through the combustion chambers and the air being pumped through, which would make the cylinder head gasket ("ZKD") more "loose" around the cylinder bores... ?

hi,
The topic has probably been discussed quite a few times.
Just use the search function.
greetings

PowerSound3L wrote:

hi, The topic has probably been discussed quite a few times. Just use the search function. greetings

Hi,

It won't fix anything (referring to something like a head gasket, etc.).

Furthermore, I've been around here almost from the beginning, and I would probably know if these aspects had already been discussed - unless it happened during my vacation, and I missed it while quickly browsing the forum afterwards.

If anyone remembers something similar, please provide a hint or the link.

Hi,

Quote:

If anyone remembers something similar, please provide a hint or the link.

So, I don't remember anything... but I've only been involved since September or October 2001, and that means probably a few weeks or months less than Ulf.

@PowerSound3L: Please read Ulf's post carefully... it was about the underlying reasons behind the issue, rather than a specific technical problem.

Best regards,

January.

Okay, I'll start from the other side.

My colleague never really cared about his cars, not about his own, and especially not about the company cars.
Specifically, this means that after a cold start, the system initiates operation at 100% of the driver's desired setting, regardless of how cold the starting conditions are.

balance sheet:
- Vehicle 1 was disposed of as a total loss due to transmission damage (approximately 80,000 km).
- Vehicle 2 was mechanically disassembled (approximately 30,000 km).
- Vehicle 3 actually experienced a head gasket failure. However, this occurred after a nearly unnoticed overheating incident during the peak of summer, when the fan switch was defective. Therefore, the head gasket failed due to the motor's cooling system malfunction.
- Vehicle 4 was a company car (1.8T) and it was driven so aggressively that it made me cry every time. It was returned after 135,000 km. Never had any problems with it.
- Vehicle 5 is now an ASZ (presumably a type of vehicle), and it's being driven recklessly as well. Especially in the winter, people say things like 'to get this damn car warm.' We'll see... so far, it has 18,000 km on the odometer.

Our quarry crew drives an MB100 to the work site every day, covering a distance of approximately 4.5 kilometers.
'This thing is indestructible. The last MB100 failed due to a structural integrity issue with the housing. However, it still served for two more years in factory service until it completely disintegrated. The engine was excellent. The machines on site have never had any engine problems. Sometimes wheel loaders are only used to load special requests, so it's like going to the bakery.'
I'm already wondering how a motor can stay sealed and not leak for 20 years in that kind of environment... grumble.

'We rarely see head gasket failures. In almost 99% of cases, the cause is an issue with the cooling system that leads to overheating. On the other hand, the turbocharger heads are known to fail if they are not treated properly (the bridge between the valves can break).'

Conclusion: ZKD devices can withstand more than ULF feared .

CU Gremlin.

Hi Gremlin.


"Yes, the MB 100s were quite strange vehicles... I hated them when I had a summer job back then. Even regular buses on the highway would get stuck behind one with a trailer."

We have this really old Mercedes 508D at my current company. It was manufactured in the early seventies. In terms of performance, it's still stuck in the Middle Ages; you practically need a flamethrower to get it moving. While it has already suffered quite a few structural damages and is used for spreading salt on roads, it will probably fall apart soon. However, the engine is still completely sealed and looks like it was just installed.
The truck has essentially only experienced short distances since it was new, and that's every day. The fact that it has 140,000 km (approximately 87,000 miles) in 30 years is quite impressive. And it's never been babied. What's also remarkable is how easily the engine starts; there's no pre-glow needed. I also suspect that all the employees are disposing of their used oil in it...
Okay, what I want to say is that this type of machine will soon be considered a large diesel engine. I believe it has an engine displacement of about 4 liters and produces 79 horsepower. Since it probably won't reach 3000 RPM, I think it will last forever. We also have someone interested in the engine; as mentioned before, the chassis is nearing the end of its lifespan!

hi,
Okay, let's discuss it then.
Therefore, if damage to the zinc-coated layer is mainly caused by the different coefficients of thermal expansion of the materials,
What about an engine with an aluminum cylinder head and an aluminum block?
For example, a Fiat Lupa 3L?
It has an aluminum block and an aluminum cylinder head.
Therefore, the ZKD (presumably a specific component) should theoretically last almost forever?
greetings

hi PowerSound3L


The problem isn't just the material and its varying thermal properties; the location of the initial heating is also quite important. Your 3L engine likely behaves the same way as all other engines in this regard. The cylinder head warms up first. However, all engine manufacturers are aware of these issues, so you can approach them with reasonable confidence. What's certainly true is the problem of cold starts and the warm-up phase. Modern engines are designed such that everything is fine when they reach operating temperature. They can also handle extended periods of full throttle without issue. It's clear that a cold start represents a completely different extreme (not in terms of pressure). Therefore, if you gently warm up your car, even without worrying about expansion, you've done everything within your control as a driver.
When you're speculating about the shear stress, which is supposedly 100%, you also need to consider the bolts that hold everything together (ZK --> ZKD --> MB --> KWG). These bolts help minimize and localize this type of stress.

PowerSound3L wrote:

What about an engine that has both an aluminum head and an aluminum block? For example, a Fiat Lupa 3L? It has an aluminum block and an aluminum cylinder head. Therefore, the ZKD should practically last forever?

Hi,

At the very least, the stress on the cylinder head gasket caused by differential thermal expansion should be significantly reduced.

If the designers calibrate the timing chain and valve system accordingly, and design it to be simpler and therefore cheaper than that of a cast aluminum engine, then the resulting aluminum engine doesn't necessarily have to be less robust.
Especially if the water cooling system fails (pump failure, water leak), the cylinder head gasket of aluminum engines is known to crack.