AHF Head Gasket Failure: Causes & Solutions

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Unfortunately, at the same time as my vehicle's technical inspection (TÜV/ASU), my head gasket failed.
After driving 20 km back (with a trailer), the coolant reservoir was empty.

How many of you drive a TDI with 110 horsepower and have already experienced a blown head gasket? If so, at what mileage and under what operating conditions?

If I only gently press the accelerator, there is hardly any noticeable coolant consumption; however, as soon as I demand power, you can watch the coolant level decrease.
When accelerating, only foam is coming out of the vent hose in the upper part of the expansion tank, which is part of the cooling system.

Too bad, I wouldn't have expected that with only 146,600 km, even though I haven't exactly taken good care of the car.

Okay, here are my questions: In the vehicle's documentation, two different types of cylinder head gaskets (2-hole) are listed for my engine (AHF in an A3, year 1998):

038 103 383 F __ >> AHF 140,000* and
038 103 383 J >> AHF 140 001*

What does the number '140,000' mean? Is it the engine number? Is it the last digits of the vehicle identification number (VIN)?
Where on the vehicle can I find this number?
Edit: I also got a notification from MBK, which is great, but I can't read it from 200 km away...

What are the differences between the two seals? Is the one labeled 'J' better?
Edit: According to the parts specialist, this refers to the arrangement of the coolant openings.
Edit2: Nonsense. The arrangement of the holes is absolutely identical, the oil return channel has a slightly larger recess, but the sealing surfaces appear to be absolutely identical, as far as I can tell.
Another difference: 'F' has 4 metal layers, while 'J' only has 3. In my opinion, there is nothing against exchanging the two gaskets with each other.

If anyone has any tips on how to quickly lower the ZK (presumably a measurement or value) without breaking your fingers...

Which, less common tools (excluding the special socket for head screws), are still worth recommending?
Even the screws that connect the exhaust pipe to the turbocharger are extremely difficult to reach...

Best regards, Rainer.

Rainer K. wrote:

Which, less common tool (excluding the socket wrench for head screws), is still worth recommending? Even the screws connecting the exhaust pipe to the turbocharger are extremely difficult to reach...

Hi Rainer,

- Use a scraper for the paved areas!
- HAzet ratchet wrench 1/2" (truly invaluable)
- Hazet universal joint wrench (always useful).
- There is now also a tool from Hazet for tensioning the ribbed belt tensioner.
- Cardan joint
- Anti-seize compound for thread sealing.
- 3/4" lever with adapter for tightening the head screws (this is where it really comes in handy).

Remove the cylinder head, including the turbocharger and return line. Spray everything with rust remover in advance.

It's only because the engine is developed quite independently of the car. They can be installed wonderfully, step by step and without the body .

Thank you for the tips!

Best regards, Rainer.

Hello,

Okay, the new gasket is now installed. After driving approximately 250 km, I can't detect any further coolant leakage.

There were no visible signs of damage to the old plaster; it looked perfectly normal.
I just noticed that the cylinder head bolts weren't as tight as I expected. Without any way to compare, I can only say that tightening the new bolts was considerably more difficult than loosening the old ones.

The condition of the cylinder bores at 147,000 km was surprisingly good (especially considering what the engine had been through). The honing marks were still very well defined, and only a small area, about the width of a piston ring, at the top dead center was slightly rough.
The pistons and valves also looked great. A quick wipe with a cloth and brush cleaner revealed the shiny aluminum underneath. A slight black pattern, showing the spray pattern of the injectors, was visible on the pistons.
Despite periods of operation with a coking index ranging from 1-30%, no visible coke formation was observed.

Between the valve seat rings and the ESDs, slight cracks of approximately 0.5mm were visible.
Well, I'm used to worse things from 1.6D ZKWs.
The cracks don't seem normal, but I'm quite sure that at least the engine cooling system has never failed.
I've now driven 350km, and the coolant level is still the same.

With the right tool (the tip about using an adjustable wrench is invaluable!), the replacement goes quite well.
Despite this, there are a few pitfalls that I fell into, and I would like to spare other people from experiencing them (AHF in the 7/98 A3):
- The ZKD (cylinder head gasket) is placed with an eyelet into the 'folded' heat shield on the exhaust manifold.
If you simply place the sealing strip on the block and then put the ZK (presumably a cover or housing) on top, the thermal insulation plate will sit on the bracket, which will then bend. The ZK cannot be mounted in this way.
- The timing belt tensioner is larger than the recess in the timing belt cover. Therefore, you have to unscrew the tensioner to be able to remove the timing belt.
It's annoying when, like me, you have the new gasket installed on the ZK (tensioner), the ZK screws are tightened, and you still have one tensioner pulley left over.
Specifically, there isn't enough space between the motor bracket and the stud bolts of the tensioner pulley to allow the part to be placed onto the stud bolts.
To avoid having to disassemble the ZK (presumably a control unit) again, I had to unscrew the right motor mount.
So, it's better to hold the gasket in the fold of the insulation plate when installing the cylinder head, while simultaneously positioning the tensioner on the stud bolt and the head on the block.
It's good to have someone to help you here.
- Since the cylinder head, intake manifold, and turbocharger are quite heavy, it's a good idea to use a wire through the mounting loops and a pulley system attached to the ceiling to lift it.
- The flexible exhaust pipe is annoying because it keeps falling down and getting stuck under the turbocharger. You then have to lift the cylinder head again to get it out. It's better to secure it with a wire towards the transmission.

To ensure that the new timing belt lasts at least as long as the old one, I've adjusted my timing setting, which was previously set "early," back a bit to 2° before top dead center (KW).

Best regards, Rainer.

Hi Rainer,

The whole thing is quite a lot of work .

Rainer K. wrote:

I only noticed that the cylinder head bolts were not as tight as I had expected.

However, due to a lack of comparison possibilities, I can only say that tightening the new bolts was considerably more difficult than loosening the old ones.

Rainer K. wrote:

Regarding the two 1Z engines that I had temporarily disassembled (with mileage of 174,000 and 270,000 km), the cylinder head bolts were also not particularly tight. In the older TD engines, loosening those bolts required significantly more force. :?Slight cracks, approximately 0.5mm in size, were visible around the valve seat rings and the ESD.

Well, I'm used to "worse" things } than 1.6D ZKs.

hmm, so, those specific 1z tires had absolutely no cracks. However, they were also driven very carefully }.

Hello Rainer,

I also just had my head gasket fail .

AFN engine in a Passat with 162,000 km (approximately 100,000 miles).
Suitable for use on long distances, with approximately 60% of the route being on highways.
I almost exclusively use biodiesel, and I haven't had any problems so far.

I can confirm that, subjectively, the screws on the cylinder head gasket were significantly easier to loosen than...
After loosening it, I needed a half-meter length of pipe as a lever to tighten it back up.

I didn't find any cracks in the cylinder head gasket, but the seal on the intermediate shaft was leaking.

'There was nothing visible on the ZKD either, except that there was a bit more of it on the 4-cylinder.'
The black plastic coating has completely disappeared, right next to the coolant channel.
I then figured out that the pressure from the combustion chamber was likely escaping into the cooling system, which was forcing the coolant out of the expansion tank.

Best regards,

Faxes.

Hello Rainer (and everyone else).

Several more questions:

You're driving the 'optimized' 110 model with a trailer. I've long suspected that the tuning doesn't really do anything unless you're driving with trailers, because you can't even fully utilize the standard 110 horsepower. The relatively short acceleration time, during which I demand full power, probably doesn't make much of a difference overall. However, when you attach a trailer, you can definitely get the engine working at its full potential of 150 horsepower for longer periods (I've already tried it, especially going up the Brennerautobahn).
'In other words, don't tune heavily loaded cars! (Opinions on this topic?)'

I still suspect that it might be useful to readjust the ZKD (presumably a technical term) values that have been in place for a while, by increasing the target value by 0%. Are there any opinions or experiences regarding this?
'In the past few months, I've seen two acquaintances with diesel cars experience what appeared to be good head gasket failures, both with mileage between 160,000 and 180,000 kilometers. (However, they were BMWs and Fords).'


I don't understand why the head gasket would fail in an engine where all the voltages have already subsided, and where the head gasket itself has been determined to be in good condition and correctly installed (otherwise, it wouldn't last the first 40,000 km). Unless the entire system is such that the clamping pressure is no longer sufficient. Higher thermal stress and boost/mid-pressure accelerate this process, but are not the real cause. This is consistent with the loose screws. It would be interesting to know if these screws could have been tightened to the specified torque before they came loose. If so, they no longer had the necessary clamping pressure.
Furthermore, it was quite common in the past to tighten head bolts. From my own experience, I can say this applies to my BMW Boxer motorcycle and my Rotax aircraft engine. The latter definitely needed it.


I found something else from Uli S:
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Here's what I've noticed: The screws on the diesel cylinder heads that I've removed so far were very easy to loosen, unlike the immense force required to tighten them. The screw is plastically deformed and, due to the constant swelling and stress, gradually loses its preload over time. It seems to be one of the common practices used by VW that eventually forces customers to take their cars to the workshop.
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garth.brooks wrote:

Furthermore, it was quite common in the past to tighten bolts

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Hi Garth,

"Previously, metal seals were not installed either . I don't think a metal seal would really work well. The problems probably arise from defects in the silicone layer ."

Hello Garth,

Quote:

However, if you attach a trailer, you can definitely use 150 horsepower (going up the Brenner Autobahn) for a longer period of time at full throttle. (I've already tried it). i.e., don't tune heavily stressed cars! ? (Opinions on this?)

Sure, I've already tried that. When you're 200km away from home with a caravan one night, and on Monday someone else has to work 200km away, your foot automatically starts to drag. I don't want to sugarcoat it, my engine is already working really hard when it's warm.
Overall, I believe the way I use my engines is somewhat unusual; unfortunately, I can't think of any way to change that, other than buying a more powerful vehicle.
That's why I'm not really surprised about the faulty head gasket. After all, a faulty head gasket is much cheaper than buying and maintaining a decent six-cylinder engine.
Just the additional fuel costs for my current vehicle would amount to €2160 (based on my current vehicle's fuel consumption of 2 liters per 1350 km, with a diesel price of €0.80 per liter). This doesn't even include the higher purchase price and vehicle tax.

A V6 TDI (perhaps not specifically an AFB engine) without the common camshaft and mass airflow sensor issues would certainly be a better choice for heavy towing.

Best regards, Rainer.

'I completely agree with you. Usually, I was one of those who would say: Before you spend thousands of euros tuning a small engine, it's better to just buy a larger machine.'

Now, from a lifespan perspective, the 4-cylinder engine is clearly the better option. It consumes significantly less fuel (why, actually?), and the lower maintenance and purchase costs likely cover even 'normal' repairs, including a head gasket replacement.

'I noticed with the early campervans equipped with TDI engines that almost all of them had already replaced their original engines with the second or third generation. The reputation of the TDI engines was so poor that many people preferred to order naturally aspirated engines instead, which unfortunately means we're now seeing a lot of old, tired, and underpowered naturally aspirated engines being used.'

From my perspective, the problem is that a motorhome can be driven at full throttle and full load for hours. (That's not the same thing.) The lifespan was probably around 70,000 kilometers. It's certainly improved since then, but I'm sure you can achieve the same effect with modifications.

What am I trying to say? I still feel good about my rather temperamental car (regarding the engine) because I only demand its full power for short bursts. Furthermore, the engine connected to the automatic transmission (that awful AG4) is inherently less stressed than one connected to a manual transmission.
However, the topic of ZKD (presumably referring to a specific technical issue) is giving me something to think about, and I'll probably adjust the expansion bolts a bit this weekend.

Here's another idea: How about creating a dedicated forum section specifically for damage reports?
I had already tried something similar before, but it was unsuccessful.
Over time, more vulnerabilities should emerge. I could probably provide about 4-5 more reports.

Regarding my question about why the 6-cylinder engine consumes more fuel: I understand that it has more parts that need to be moved, but roughly speaking, the effect should be around 0.3 liters, not 1-1.5 liters. So, WHY is that?

Hi,

garth.brooks wrote:

...One more thing: How about creating a dedicated forum section just for damage reports? I had already tried something similar before, but it was unsuccessful. Over time, more vulnerabilities should become apparent. I could probably contribute 4-5 more reports.

I'm open to that, at least then you would know what to expect with individual engines.
- Timing belt gear may be loose on AAZ/1Z engines; check the screw and its tightness.
- Timing chains/high-pressure fuel pumps in some V6 TDIs.
...

garth.brooks wrote:

Regarding my question about why the 6-cylinder engine consumes more fuel - I understand that it has more parts that need to be moved, but roughly speaking, the effect should be around 0.3 liters, not 1-1.5 liters - So, WHY?

How about the frictional power loss of the 2 additional cylinders?
Furthermore, the engine, and indeed the entire vehicle, is significantly heavier.
The V6 engine is only available in the A4, A6, and Passat classes. It weighs considerably more than an A3.
The transmission for the V6 TDI engine needs to be more robust and, consequently, heavier.

Best regards, Rainer.

Hello Rainer,

That's what I meant by the 0.3 liters more – the additional moving parts, such as the two cylinders, more camshafts, etc.

Assuming that a 4-cylinder engine requires approximately 0.6 liters to rotate itself (i.e., without a load), the 6-cylinder engine should require a maximum of 50% more, but practically less, since the load on components like the water pump, alternator, and oil pump doesn't increase proportionally. The fuel consumption of the AFN engine block itself, excluding the aforementioned auxiliary components, could be around 0.3 liters, which would translate to 0.45 liters for the 6-cylinder engine, an increase of 0.15 liters. (What does VAG-Com actually say about the fuel consumption at idle for the 6-cylinder engine?)

The engine weighs less than 50 kg. For every 100 kg, you use approximately 0.6 liters, so that's 0.3 liters.

The transmission is the same depending on the type. Roughly, I can explain a maximum of 0.5 liters.

So, to reiterate: Why is the 6-cylinder engine consuming so much fuel? - Up to 2 liters more?

Could one assume that a 2-cylinder TDI engine would consume 2 liters less fuel than a 4-cylinder engine? Probably not, right?

Hello Rainer,

As threatened, I tried to tighten my ZK screws, as I suspected it might be a good idea.


Even with 10% more force, they couldn't be turned - so they are stuck.

Why were they so easy to remove from you after the ZKD damage?

Hello,

Remember that the 0.3 liters likely refers to the idle speed, not 3000 RPM. In addition to the increased friction, the 2.5L engine pumps a significantly larger amount of unused air through at partial load.

For gasoline engines, you can also estimate an additional fuel consumption of approximately 1 liter per additional cylinder.

Best regards,
Christian.

garth.brooks wrote:

Hello Rainer, That's what I meant by the 0.3 liters more – the additional moving parts, such as the two cylinders, more camshafts, etc. Assuming that a 4-cylinder engine requires approximately 0.6 liters to rotate itself (i.e., without a load), the 6-cylinder engine should require a maximum of 50% more, but likely less, because the load on components like the water pump, alternator, and oil pump doesn't increase proportionally. The fuel consumption of the AFN engine block itself, excluding the aforementioned auxiliary components, could be around 0.3 liters, which would translate to 0.45 liters for the 6-cylinder engine, an increase of 0.15 liters. (What does VAG-Com actually say about the fuel consumption at idle for the 6-cylinder engine?) The engine weighs less than 50 kg. For every 100 kg, you use about 0.6 liters, so that's 0.3 liters. The transmission is the same, depending on the type. Roughly, I can explain a maximum of 0.5 liters. So, to reiterate: Why is the 6-cylinder engine consuming so much fuel? - Up to 2 liters more? Could one assume that a 2-cylinder TDI engine would consume 2 liters less fuel than a 4-cylinder engine? Probably not, right?