Second head gasket failure?

Hello,

A few months ago, I had to replace the head gasket on my AFN engine because coolant was leaking into the combustion chambers. It started with gurgling noises in the heater after the car had been stationary for a while, and ended with a significant coolant loss. After the head gasket replacement, there were no more noises and no more coolant loss. Now, the noises are back. This is very concerning. I will now carefully monitor whether the coolant level drops again.
Based on your experience, do you think it makes sense to retighten the cylinder head cover bolts?
Should I assume that the head might still be misaligned, and therefore could become leaky again?

Regards,
Martha.

Hello,

The problem is that it's usually too late by the time it becomes noticeable.

You can always follow up, but it's unclear whether it will make a difference. It doesn't cost anything, though.

Suggestion: Check the cylinder head gasket.

In a gasoline engine, the air-fuel mixture was introduced into the cylinder by compressed air. In this case, for example, by using an old glow plug with a hole drilled through it, then check to see if it's bubbling in the coolant.

I'm not sure if that's a meaningful indicator for diesel engines, given the higher pressures involved.


If it's leaking, tighten it and check again, but even if it's tight then, how long will it last?


Good luck.

Hello,

Metal head gaskets are actually quite robust.
It's therefore not unlikely that something else went wrong. Using compressed air for testing might be okay, but the combustion pressures in a diesel engine are over 60 bar. Therefore, it doesn't mean much if a leak initially appears to be sealed again when pressurized with a few bar of compressed air.

Sure, here's the translation:

"Two more questions:"

Did you use new screws?
Was the head examined for cracks?

Sincerely,
Christian

Hello,

'I carried out the repair myself at the beginning of the year. I only visually inspected the cylinder head; everything seemed okay. It worked fine until now, when this unpleasant bubbling noise has started again. Of course, I used new screws.' I also cleaned the head and block until I was driven crazy, using razor blades, sandpaper, and other abrasive materials.
Regarding my previous question about tightening: Could it happen that these expansion bolts break if I tighten them another quarter turn?

A little while ago, I drove a few kilometers fairly quickly (around 200 km/h) over the tracks. Immediately afterward, I opened the radiator cap, and there wasn't any significant pressure inside. Before I replaced the gasket, the car would immediately spew out large amounts of coolant under the same conditions. So, maybe I'm worrying about nothing? You probably have to wait and see.

Oh man, give me back my 1988 35i with its amazing RP engine. After 14 years and 220,000 km, there weren't the slightest problems. Does anyone happen to have something like that to give away?

Regards,
Martha.

Martha wrote:

Razor blades, abrasive cloths, etc.

Hi Martha,

I can only recommend investing a few euros and buying a Hazetschaber for this purpose; anything else is bordering on shoddy workmanship . Using sandpaper should only be done on disassembled valves, covering the entire head.

Martha wrote:

Regarding my previous question about tightening: Could it happen that these expansion bolts break if I tighten them another quarter turn?

"Someone in the forum once mentioned that a VW dealer had tightened the head bolts on a TDI engine. However, I'm a bit skeptical about that, as my understanding is that the clearances between the closed valves and the pistons are minimal." "However, the screws should definitely be able to withstand a quarter turn (at least, the forces felt significantly greater when tightening the old TD screws after 1000 km compared to the TDI screws - NOTE: NOT REQUIRED for the TDI!!!)"


"What torque wrench did you use to tighten the screws? How did you estimate the tightening angle? Were the sealing surfaces 100% free of grease?" What grit did you use?

Martha wrote:

Should I assume that the head might still be misaligned and therefore become leaky again?

As long as the engine hasn't overheated, this is relatively unlikely. Based on my experience with TDI cylinder heads, cracking between the valves is a problem that seems to be a thing of the past (->TD).

Hi,
It could also have another source of error: sometimes the threads in the head are corroded and need to be re-cut (cleaned) with a tap.
Theoretically, it could also be that one of the cooling channels is blocked, which causes the head to heat up unevenly and expand. I don't know if something like that has actually happened before.

christians wrote:

Sometimes, the threads inside the head are corroded and need to be re-cut (cleaned) with a tap.

Hi Christian,

Which threads are you referring to (->Block)? In the area of head screws, there are no threads on the ZK .

It is absolutely necessary to ensure that no oil or water is present in the threads within the block. Otherwise, the enormous torque can cause cracks in the area of the threads .

Hello everyone,

I drove over 300 km on the highway at a higher speed this weekend. No coolant was lost. Perhaps the occasional air noise during startup has different causes than a faulty head gasket. For example, I heard from an owner of a Mercedes W123 that it was due to a defective heater heat exchanger in his case. It slowly but surely leaked, and when the valve was first opened, it was refilled with coolant with a gurgling sound (Of course, I know that in my vehicle, the heating is controlled secondarily, so it cannot be the cause).#

Regarding your questions: I pre-treated the screw holes to ensure they were dry, and I believe I adhered to the specified torque and rotation angles quite well (although I cannot guarantee this specifically for the arc second ). I no longer remember the grit size. Probably around 600.

Quintessence: For now, I won't take any action and will continue to observe the situation. If it turns out to be a serious defect again, I will seriously consider going back to a proven and less demanding vehicle, one that comes from an era where even a small number of highly complex systems on board results in a significantly lower failure rate, and where repairs can be carried out with a fraction of the effort.

Regards,
Martha.

Hi,
"Of course, I meant the threads in the block, not in the head."

Hi,
Could it be that there's still air trapped in the heating system's heat exchanger after the repair?
With the warm weather we've been having in recent weeks, you probably turned off the heating. But now it's getting colder... (Even air-conditioned heating systems often have a water valve to provide truly cold air in the summer.)

Hello Christians,

That is the straw I am clinging to .

Regards,

Martha.

Hello everyone,

The straw seems to be holding. I've now driven over 1000 km without any coolant disappearing. I also haven't heard that gurgling sound for a long time. It seems there was still some room for improvement somewhere within the system.

Regards,
Martha.