AJM: Coolant Leak, Head Gasket - Questions

hb2000 wrote:

The good old AJM and the problem with the missing coolant. ... At high speeds and/or loads, exhaust gases are increasingly forced into the cooling system, which causes the pressure in the cooling system to become too high, and the coolant escapes through the valve in the expansion tank cap. I understand your description of "driving 50km on the highway and then the tank is empty," because my Passat does the exact same thing with the coolant. As I said, it's not being burned by the engine, but rather escaping due to excessive pressure in the cooling system. You probably also have that strange gurgling sound "somewhere in the dashboard" - that's the air in the cooling system that you hear in the heat exchanger. I hope I could help a little, even though I would have preferred to write something positive. It's likely that the head gasket is only defective in this one specific area, and the oil and water have remained separate for over 15,000 km.

Hello,

My AJM engine has exactly the same symptoms as described above and in many other threads. Therefore, I know that I need to replace the head gasket next weekend. However, I have one more question that's been bothering me:

I find it astonishing that gas from the combustion chamber could escape into the water cooling system over an extended period without being noticeable in the coolant itself. Could it be possible that the cylinder head has a crack that allows air from the area in front of the intake valves to enter the water cooling system under certain boost pressures? This could explain the clean water and also why the gurgling sound often occurs at higher RPMs (boost pressures). The maximum boost pressure of the AJM engine (approximately 1.2 bar overpressure) and the maximum pressure in the water cooling system (the pressure relief valve in the cap opens at 1.2 bar overpressure) are somewhat comparable.

Does anyone know if such a crack is even possible, i.e., whether the coolant and fresh air are close enough to each other in the cylinder head?

I think a CO2 test in the cooling circuit could clarify whether it's combustion gases or charge air, but I won't be able to do that for a few days. If the test doesn't detect any CO2, I can't think of any other hypothesis, assuming the seals and the pressure relief valve on the water tank are in good condition.

Thank you for your input.

Martin.

Hi.

A CO2 test for diesel vehicles is often borderline and may not provide a reliable result.

And often, when the engine is off, water can leak into the combustion chamber if there is still pressure in the cooling system, but the combustion chamber is at atmospheric pressure. This is why there is also a risk of bent connecting rods due to water hammer when starting the engine.

I once experienced something similar with a RA engine in a Golf II GT Special TD with an intercooler that my former boss installed because he wouldn't listen to advice.

Hello Martin,

Based on my own experience, leaks in the cylinder head gasket or cylinder head are often not immediately apparent when looking at the coolant.
It only becomes apparent in cases of severe water loss or oil/water mixtures.
My engine, which was affected at the time, an AHF, was completely normal in this regard. Also, coolant loss only occurred when a certain engine load was consistently exceeded; you could "tucker" along for a long time without any issues.

Best regards, Rainer.

Hello,

Thank you for your input!

Why is the CO2 test for diesel vehicles not conclusive?

I know of a blown head gasket on a JP/JR engine, characterized by a lot of dirt in the water and, most importantly, distinct bubbles, at least when the engine has been running for a while. In this case, the "leak" in the gasket must be quite small, because I have few problems at low load, but I notice it quite clearly when driving uphill on the highway.

How much additional labor time would you estimate for replacing the timing chain cover (TCC) *in addition* to replacing the timing belt? I can now do the timing belt replacement in my sleep, given the maintenance interval.

Regards,
Martin.

Hello Martin,

7111 wrote:

How much additional labor time would you estimate for replacing the timing cover gasket, *in addition to* replacing the timing belt?

It's difficult to estimate the cost upfront because you don't know how severe the damage is before removing the cylinder head. Whether a gasket is installed in the cylinder head or not, whether there's a crack in the cylinder head or not...

Personally, I would estimate an extra half-day, but only because I don't do it very often. There are labor time calculation programs for workshops that specify the time required for certain tasks on a particular model. Perhaps someone from the workshop area can provide an estimate of the labor time involved.

Best regards, Rainer.

The symptoms perfectly match those of a blocked catalytic converter... Pressure builds up and it sputters only under increased load, just as Rainer described.

Quote:

Personally, I would calculate an additional half day

.
I completely agree. It's crucial to ensure that the turbocharger is properly drained of oil before reassembly, so that no oil gets between the seals. Additionally, dismantling the components around the turbocharger can be time-consuming due to potentially corroded screws.

Possibly, the cylinder head still needs to be ground, which would incur additional labor costs.

What I definitely recommend is cleaning the engine thoroughly with a pressure washer beforehand.

I would probably plan for two days, just to be on the safe side.

Okay, thanks. This will help create a plan.

Hello,

Sure, here's the translation:

"A little feedback:"

The 2 days needed for a complete cylinder head replacement would be sufficient, provided the screws aren't seized. The cylinder head, along with its attachments, can be easily lifted and reattached by oneself using a pulley system.

Problematic issues included: a stud on the exhaust flange near the turbocharger, the top screw of the rear timing belt cover (M8 with a 6mm Allen key), and the fitting of the oil line to the turbo.

No visible cracks in the head; head deformation is clearly below 0.1mm.

Regards,
Martin.

Hello,

It's best to spray a MOS2 rust remover on heavily rusted parts 1-2 days beforehand and let it soak in, making sure the oil doesn't burn. If the area is heat-sensitive, do not run the engine after spraying.
Generally, fittings are easier to loosen when the engine is warm. Of course, using proper tools is essential; for example, using worn-out socket wrenches will only cause problems.

Best regards, Rainer.

In the case of the exhaust flange, I applied rust remover for a long time *before* I started working on it, and I also got a new hexagonal nut, but there was nothing I could do. Neither heating it with the gas burner nor welding a nut onto it worked. The solution was to file away the material on both sides until I reached the threads, and then use a hammer and chisel to loosen it. The stud bolt survived.

The nut located above the oil inlet on the turbocharger bearing was likely stuck fast due to the different metals and the fact that water can sometimes accumulate there. Today, at the junkyard, I saw two other cars with the exact same problem...

Regards,
Martin.

Hello,

Here's a little feedback to close the thread: After replacing the head gasket, all the symptoms disappeared, and in the 6,000 km since then, even with very high outside temperatures of up to 45 degrees Celsius, no further problems have occurred. The car (Passat 3B Variant) and the engine now have 440,000 km on the odometer.

Thank you again .

Martin.