Problem with Sirocco (Auxiliary Heater)
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Mercedes ML350 W166
Problem with Sirocco (Auxiliary Heater)
Hello everyone,
I own a 2012 Mercedes ML350 W166 and I’m facing a strange issue with the Sirocco (auxiliary heater / Webasto).
Last year it worked perfectly — it heated the car very well, and even on cold mornings (around -10°C) the interior was warm.
Later that same year, the car suddenly stopped producing any heat inside.
I found some glass-like granules in the cooling system.
I completely flushed the system (changed the coolant about 10 times until everything was clean), then replaced all circulation pumps and the thermostat.
The cabin heat came back, but not as strong as before.
I went to several service shops, and after some work the heating improved, so I left it as it was. During warm weather, it worked fine — the issue mainly appeared in cold conditions.
Now, this year, the cabin heat seems OK when the engine runs, but the Sirocco, when programmed in the morning, barely warms the air inside.
Before, it used to heat the interior very well.
The Sirocco starts normally, I can hear it running, no fault codes appear on the diagnostic tool, but it only slightly warms the air.
I checked the pumps again, ran diagnostics, and verified temperatures — everything seems fine.
Still, the heating performance is clearly reduced.
Has anyone experienced something similar?
Any advice or experience would be greatly appreciated.
I own a 2012 Mercedes ML350 W166 and I’m facing a strange issue with the Sirocco (auxiliary heater / Webasto).
Last year it worked perfectly — it heated the car very well, and even on cold mornings (around -10°C) the interior was warm.
Later that same year, the car suddenly stopped producing any heat inside.
I found some glass-like granules in the cooling system.
I completely flushed the system (changed the coolant about 10 times until everything was clean), then replaced all circulation pumps and the thermostat.
The cabin heat came back, but not as strong as before.
I went to several service shops, and after some work the heating improved, so I left it as it was. During warm weather, it worked fine — the issue mainly appeared in cold conditions.
Now, this year, the cabin heat seems OK when the engine runs, but the Sirocco, when programmed in the morning, barely warms the air inside.
Before, it used to heat the interior very well.
The Sirocco starts normally, I can hear it running, no fault codes appear on the diagnostic tool, but it only slightly warms the air.
I checked the pumps again, ran diagnostics, and verified temperatures — everything seems fine.
Still, the heating performance is clearly reduced.
Has anyone experienced something similar?
Any advice or experience would be greatly appreciated.
