TDI Timing Chain Replacement Guide A4

Hello everyone,

'I've experienced the problems discussed here with my A4 AFN, manufactured in 1997, namely the bubbling sound in the dashboard and the coolant gurgling at higher RPM/load. I suspect the head gasket is blown.'

Is there anything specific to keep in mind when replacing the head gasket?
I have successfully performed this procedure on a T3 diesel, an Audi 100 TD, and several gasoline engines. So, I'm not completely inexperienced.

Best regards and thank you for the information.

Thomas Meyer.

meyert wrote:

I've already discussed the problems mentioned here with my A4 AFN, manufactured in 1997, regarding the water bubbling in the dashboard and the coolant gurgling at higher RPM/load.

I assume the head gasket is gone.

Hi Thomas,

Mileage???

Are you sure it's the head gasket? It's not made of plastic like it used to be with TD and others; it's made of metal with a silicone coating, and it usually doesn't break. Unless the engine was overheated, which could warp the cylinder head, or there was excessive tuning/modification. Have a carbon monoxide test done, etc. I can hardly imagine that's the problem!

Otherwise, the work is the same as with the TD (except for disconnecting a few extra cables }), and in some cases, even a little easier (at least when comparing the Passat TD/TDI)!

Best regards, Christian.

Hello Christian,

Thank you for your suggestion.

The mileage is 212,000 km. I took over the car from a friend (company car) when it had 190,000 km. He mainly drove it on long distances, quickly but definitely not recklessly. I myself was satisfied with the engine power of my old 200D. That's my driving style. There's definitely no tuning involved.

I still believe the problem is quite clear. There is absolutely no leakage, neither from the water pump, nor any smell or puddles of coolant inside the car or anywhere else in the engine compartment. Instead, the water is being forced out of the expansion tank as soon as I get on the highway.
As a last-ditch effort, I added radiator sealant (Bars Leak). Since then, the coolant foams like whipped cream from the overflow tank whenever I open the cap with a warm engine.
The leak hasn't changed. Also, air is still accumulating in the heating system, which is causing hissing noises in the dashboard. There's no oil in the water, and no water in the oil, so it seems there's only compression in the water.

I can't think of anything else besides the ZKD.

I had already consulted with a specialized workshop. The mechanic examined the vehicle and found white crystals at the hose connection to the expansion tank. He was immediately certain that the tank was defective and needed to be replaced. I politely declined, later removed the hose, cleaned off the crystals, and inspected the tank: there were no signs of damage. The crystals also haven't reappeared. So much for the specialized workshop. Apparently, they only repair things by randomly replacing parts. I could do that myself too. My initial suspicion is the head gasket. Next, I would suspect a hairline crack in the head (no, I really don't want to think about that).

Regards,
Thomas.

meyert wrote:

There is absolutely no leakage, neither from the water pump, nor any smell or puddles of coolant inside the car or anywhere else in the engine compartment. However, it pushes water out of the expansion tank as soon as I get on the highway.

Hi Thomas,

Consider that, for example, the pressure cap on the expansion tank contains a pressure valve that often breaks, leading to too high or too low pressure. Furthermore, the G12 coolant (red, if you have it) is hardly visible on the engine block, in my opinion. At least, I recently spilled about a liter of it on the engine block while replacing the temperature sensor, and afterwards, there were no more of those large, white deposits like before!

This radiator sealant is complete garbage... this stuff just clogs up important openings .

Okay, try this test: Carefully open the warm engine's expansion tank and have an assistant give it full throttle (if the timing belt is in good condition, otherwise 3000 rpm should be sufficient). If it bubbles, it definitely indicates a blown head gasket.

Ulf also suggested another test in this forum: (I believe) turn off the engine with the expansion tank open and see if the coolant level changes .

....then we'll see. If you're unlucky, it could also be a crack in the cylinder head, but let's not jump to conclusions just yet .

Best regards, Christian.

Check if pressure is building up in the system (by squeezing the hoses). If no pressure builds up, the problem might start to "boil" over!

Okay, one more thing: the issue with the expansion tank isn't entirely wrong. The connection point where the vent hose is attached sometimes breaks off -> I experienced this with my Audi 80 1Z, and also with my old TD -> this prevents pressure buildup!

Best regards, Christian.

Hello Christian,

1) I can confirm what was said about G12: it's barely possible to see any tracks.

2) den Deckel würde ich ausschließen, weil sich erstens sehr schnell Überdruck aufbaut und zweitens das Ventil den Druck auch wieder abläßt (halt mit Wasserkötzeln ;-)). Außerdem habe ich auch mal probiert, den Deckel nur aufzulegen und nicht zuzuschrauben. Somit kein Überdruck. TrotzdeI don't understand.

3) The temperature gauge always remains stubbornly fixed at 90 degrees when the engine is running.

4) I had already performed a bubble test. Large air bubbles form and then rise into the expansion tank. In my old diesel T3 with a blown head gasket, it looked different: it bubbled violently out of the expansion tank like boiling water in a pot. However, I noticed back then that the bubbling effect depends not only on the engine speed, but also on the load. Therefore, a test at idle might be questionable.

5) Performing a ZKD test by measuring the coolant level after the engine is turned off sounds quite adventurous.

6) I am all too familiar with the problems related to the expansion tanks and overflow hoses in VAG vehicles from the 70s and 80s. Nevertheless, I'm not convinced to replace the tank as a precautionary measure.

Regards,
Thomas.

Hello Christian,

I just went back to the VW-VAG mechanic. It felt more human there than at the glass and metal palace at AUDI, which is part of the same VAG group. Even the master mechanic seemed less arrogant. No spread fingers and condescending chatter. ;-)

Definitely: The radiator cap has been checked and is completely fine. They probably don't break easily. The problematic ones were the black, semi-circular caps, roughly up to the year 1990.

According to him, the problem is a classic ZKD (head gasket) failure, as classic as it gets. It will cost 600 euros to fix if the head isn't damaged. A new head costs 1800 euros. I bought some screws and gaskets, and I'll start working on it on Saturday. I'll keep you updated.

Regards,
Thomas.

Hi Thomas,

Okay, then it almost looks like a ZKD . You should also look for cracks when removing the cylinder head. This is a good opportunity to check the glow plugs (I had two defective threads when I removed it, so I had to remove the cylinder head ). I would also replace the valve stem seals at the same time! Unfortunately, I haven't found an ultimate solution for cleaning the sealing surfaces -> Hazet scraper.

You can then also clean the intake area (it's a messy job) and then damage the EGR valve .

The torque sequence (AAZ, 1Z, AFN) is 40Nm, then 60Nm, then twice 90° (according to the usual tightening pattern). Retightening on a warm engine (as before) is NO LONGER required .
Maybe get a protractor... I've only ever estimated the angle of rotation so far, which (hopefully) is enough . Good luck.

Best regards, Christian.

meyert wrote:

According to him, my problem is such a classic ZKD (cylinder head gasket) failure, as classic as it gets. It will cost 600 euros if the head isn't damaged. A new head costs 1800 euros. I bought some screws and gaskets, and I'll start working on it on Saturday. I'll keep you updated.

"Please fix it quickly. The head gaskets are from Elring or DPH, and they are much cheaper from parts suppliers! There are companies that specialize in instant engine rebuilds that sell a rebuilt head (without camshaft) for as little as 300 euros. Just don't go to www.motorensuche.com... -> Saftl... I had serious problems with them -> involving a lawyer, etc."

However, it's still strange that a metal head gasket would fail at that mileage (was it driven hard?).

Best regards, Christian.

Hello Christian,

As mentioned above, there's definitely no sign of the engine being 'warmed up' properly. However, I do find 210,000 km (approximately 130,000 miles) to be quite a high mileage, so a faulty head gasket wouldn't be entirely surprising, would it?

I'll hold off on dealing with the valve stem seals for now. So far, there's no significant oil consumption and no noticeable smoking.

I'll take a look at the glow plugs, but I'm wondering if there's a gasket on the intake manifold that needs to be replaced.

Are you sure about the torque specifications? The 'Do-it-yourself' guide mentions retightening the bolts when the engine is warm.

Of course, a replacement cylinder head from VAG is not an option. If necessary, I would certainly resort to a cheaper alternative. However, getting the cylinder head gasket directly from VAG gives me more confidence than buying one from a random parts store.

Regards,
Thomas.

Hi Thomas,

meyert wrote:

I'll take a look at the spark plugs, but I'm not sure about them.

By the way, is there a gasket on the intake manifold that needs to be replaced?

There is a complete gasket set (including shaft seals) available from Elring or DPH for the price of a single head gasket (from the same company) at VW

meyert wrote:

.

Are you sure about the torque specifications? The "Do it yourself" guide mentions retightening them with a warm engine.

Certainly . I also have the Erwin (siehe Fehlerdatenbank) repair manual for AFN, 1Z, and AAZ engines!! A metal head gasket does not need to be retightened . These...books are useless...I have the "How it's done" book, and it's one mistake after another

meyert wrote:

.

An exchange head from VAG is naturally out of the question. If necessary, I would of course resort to a cheaper option. However, getting the head gasket directly from VAG gives me more confidence than getting one from some random parts store.

meyert wrote:

Well... it should be fine. The old TD cylinder heads generally had cracks between the valves... I didn't have any cracks in mine (175,000 km). It's probably due to the better design or the metal head gasket. Let's see how it is with yours.

as mentioned above; there is definitely no sign of the engine being "warmed up" properly. Nevertheless, I don't think 210,000 km is a particularly low mileage, so a defective head gasket wouldn't be that surprising, would it?

So, the people I know who own TDI vehicles have driven well over 250,000 km and have never had any problems with the head gasket. Also, I'm not aware of anyone in the forum who has experienced this issue! Of course, the old gaskets were a problem because they would compress over time (->which is why they needed to be retorqued). Metal gaskets don't do this. Perhaps the silicone layer was damaged during installation, which could be due to manufacturing tolerances .

When removing the head, make sure there is no oil left inside, otherwise you will end up having to remove oil from the expansion tank.

Best regards, Christian}

You can ignore the bracket with the credit card information... it sometimes appears automatically here .

Hi Thomas,

I need to correct myself again... if you enter "cylinder head gasket" in the search function, there are a few cases that come up; strangely, they all involve the AFN engine. The cylinder head and gasket are probably the same as on the 1Z engine. Perhaps the extra 20 horsepower is enough to cause the gasket to fail more quickly than it would on a 1Z engine.

Best regards, Christian.

Hello Christian,

Thank you for the tip about the torque setting. I also got a copy of 'How it's done,' and it's in there just as you described.

It's probably always a matter of how up-to-date the information in the manual you have is. It's quite likely that Etzold and Korb are both using information from the repair manual. However, that manual probably changes from time to time. Therefore, an online subscription from Erwin (siehe Fehlerdatenbank) would probably be more useful than the CDs.

Okay, 'Headless' starts this afternoon. I'll keep you updated.

Regards,
Thomas.

Hello Christian,

The replacement of the water pump is complete. :D. It was successful. The water stays inside, and the hissing sound from the dashboard is gone.

The whole process was a terrible ordeal. The first disappointment was the continuous separating plate between the timing belt and the engine block: The camshaft sprocket has to be removed. I've never encountered that before. So, first, I need to build a setting gauge!
The biggest problem was during the assembly of the turbocharger's oil return line. It probably wasn't a good idea to disconnect the return line from the turbo itself instead of from the oil pan. Either way, it took hours to get the screws in. I was about to go crazy!

Only the adjustment of the start time of the boost remains. When it gets warmer, I will take the PC outside and measure it with VAG-Com according to Ulf's diagram. Although, purely subjectively, I have the impression that it is absolutely perfect as it is now. The wisest thing would probably be to leave it as it is, because it can really only get worse. But probably curiosity will win in the end :wink:.

Best regards, Thomas.