AHU engine in Caddy experiencing issues at nearly 400,000 km

Hello fellow diesel mechanics,

After praising my Caddy, I'm now afraid that something really bad is about to happen.
When starting the engine cold, it only runs on 3 cylinders and produces 'grayish-dark gray' smoke.
After a few hundred meters (I'm suffering with this Caddy), the 4-cylinder engine kicks in.
I thought the 'nozzles' were the problem, and I replaced them, but unfortunately, it didn't work. New nozzles would definitely make a difference. The AHU (Air Handling Unit) is working okay when all four burners are running.

I suspect it might be a 'head gasket' issue, but a few things actually argue against that: there's absolutely no water loss, and a head gasket that has blown will always be damaged, even when cold.
Given the significant increase in oil consumption, I suspect the hydraulic lifters.

Perhaps someone can offer me some advice, or maybe someone has another idea.

Thank you very much for your help in advance.

Best regards,
TT - Diesel.

Well, at 400,000 km, I would simply check the compression.

Are the original nozzles still installed?

It might also be a combination of poor compression and a faulty fourth glow plug, and/or a poor spray pattern from the affected injector. (It's possible that the other three cylinders are only running stably when the engine is cold due to the afterglow function.)

Hello,

I have replaced the nozzles, as mentioned before.

I haven't checked the compression yet, but I don't think it would be okay even if there was a problem with a hydraulic lifter. It's definitely something that needs to be checked.

The 400,000 km mileage shouldn't be a problem; this is a vehicle designed for long distances. It's currently 6 years and 3 months old. It has received full servicing every 25,000 km, using 5W-40 brand-name synthetic oil, along with oil and air filters. Additionally, a diesel filter is replaced every 50,000 km, and the timing belt with tensioner is replaced every 100,000 km.

Turning back to the topic of compression, the performance seems to be fine, and it doesn't appear to be related to the compression itself. The acceleration is adequate, even in highway traffic, and the top speed (192 km/h according to the speedometer, which is likely a 'Caddy' modification) is easily reached.

I would appreciate any further suggestions.

Regards,
TT - Diesel.

Hi,

Hydro wäre möglich, dazu müsste er aber wenn er länger steht ganz leer sein-macht sich aber beim Start lautstark bemerkbar.Zum Ölverbrauch; leider gibt es mehrere Möglichkeiten: Ventilschaftdichtungen (billigste),Turbolader, oder auch Ölabstreifringe (Kolbenringe) - hab ich was vergessen??{MARKERBitte gib mir den deutschen Text, den du übersetzt haben möchtest.
Best regards,

Hello.

If a cylinder fails only after several hundred meters, then the glow plug system can be ruled out as the sole cause. A compression test should be performed, which, given the mileage, will likely show low pressure levels in all cylinders.

If the oil consumption is caused by the piston rings, it should be visible in the exhaust emissions. What is the oil consumption rate, and is it related to the poor starting quality? How does it behave at higher temperatures now?

Hello everyone,

The oil consumption has now increased to 3/4 liter per 1000 km, when driving at a faster pace (3500 RPM).

I've decided to start by replacing or repairing the valve stem seals and the hydraulic lifters. This can all be done without removing the cylinder head.

After that, I will perform a compression test. Then we will see how things progress.

I will keep you updated as soon as I have new information. It will definitely be after Pentecost.

If necessary, I will also overhaul the engine, which includes replacing the piston rings (provided the cylinder wear is still within tolerance) and the connecting rod bearings and crankshaft bearings.
The cylinder head would already be fixed (repair of the hydraulic lifters --> the valves must be sealing properly).

If the forum administrators require it, I can also provide documentation and take photos, please let me know.

Regards,
TT - Diesel.

Hello everyone, once again.

I forgot to include something earlier.

In January, I had the vehicle inspected (TÜV) for its main inspection (HU) and emissions test (AU). At that time, the oil consumption was already at 1/2 liter per 1000 km. The emissions test was fine, with very good results, as you would expect for a vehicle that's driven long distances.
Vehicle common.

'I also noticed that the valves are making a rattling noise. When I give it a little gas, the noise stops, but then when the engine is idling, you can hear the valves rattling again (when the engine is cold).'

Okay, here's the translation:

'And one more question: I need a good supplier for replacement kits for the hydraulic lifters or valve stem seals.'

Thank you in advance.

Regards,
TT - Diesel.

Quote:

Der Zylinderkopf wäre schon gemacht ...

Hi,

If I'm not mistaken...

If you disassemble it, please also check the valve stem seals. At that mileage, I wouldn't be surprised if they were quite worn (usually on the exhaust side).

Regards