W166 ML350 weird behavior
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W166 350
W166 ML350 weird behavior
Hello community,
I’ve got W166 ML350 blueefficiency petrol with m276 engine.
These days I’ve noticed a thing and I’m curious if it’s an issue or not.
So I start the car (cold start) and is working a bit noisy (only 2-3sec rattle at first start and no knocking or other), just higher rpm and a bit noisy.
I walked around the car and while I was behind it I’ve heard a quiet click (like from a relay) and the sound of the car goes quieter and smooth. This happened maybe a few minutes after the start.
Now I wonder if thats normal thing or not? Anyone have the same experience?
Also want to rule out low oil pressure.
I’ve got W166 ML350 blueefficiency petrol with m276 engine.
These days I’ve noticed a thing and I’m curious if it’s an issue or not.
So I start the car (cold start) and is working a bit noisy (only 2-3sec rattle at first start and no knocking or other), just higher rpm and a bit noisy.
I walked around the car and while I was behind it I’ve heard a quiet click (like from a relay) and the sound of the car goes quieter and smooth. This happened maybe a few minutes after the start.
Now I wonder if thats normal thing or not? Anyone have the same experience?
Also want to rule out low oil pressure.
Last edited by Casper666; Feb 16, 2026 at 09:30 AM.
Junior Member
Joined: Sep 2025
Posts: 49
Likes: 20
That is normal. The loud idle and rattle for a few seconds is just the engine warming up and the emissions system doing its thing.
The quiet click you hear is the secondary air injection pump shutting off. It pushes air into the exhaust to heat up the cats quickly on a cold start. When it turns off, the engine gets quieter and smoother.
Nothing to worry about.
The quiet click you hear is the secondary air injection pump shutting off. It pushes air into the exhaust to heat up the cats quickly on a cold start. When it turns off, the engine gets quieter and smoother.
Nothing to worry about.
Thread Starter
Newbie
Joined: Aug 2025
Posts: 5
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W166 350
That is normal. The loud idle and rattle for a few seconds is just the engine warming up and the emissions system doing its thing.
The quiet click you hear is the secondary air injection pump shutting off. It pushes air into the exhaust to heat up the cats quickly on a cold start. When it turns off, the engine gets quieter and smoother.
Nothing to worry about.
The quiet click you hear is the secondary air injection pump shutting off. It pushes air into the exhaust to heat up the cats quickly on a cold start. When it turns off, the engine gets quieter and smoother.
Nothing to worry about.
I thought it may be the sai pump but I think I don’t have one.
Junior Member
Joined: Jun 2021
Posts: 53
Likes: 10
From: Columbia, MO
2001 SL500, 2017 GLE350
There is also the part where Mercedes put a solenoid in your oil pump so that the pump cannot go to full output (4 bar) until 3500 rpm and above, where your engine rarely goes during regular driving. Full output is 4 bar, but Mercedes is grasping for fuel milage uber alles, so you don't get decent oil pressure. 2 bar for you. Plenty of info out there, including info on how to disconnect the solenoid, forcing full oil pressure at all times (including startup/warmup, where it might be useful). But hey, just an opinion, YMMV, etc
Thread Starter
Newbie
Joined: Aug 2025
Posts: 5
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W166 350
There is also the part where Mercedes put a solenoid in your oil pump so that the pump cannot go to full output (4 bar) until 3500 rpm and above, where your engine rarely goes during regular driving. Full output is 4 bar, but Mercedes is grasping for fuel milage uber alles, so you don't get decent oil pressure. 2 bar for you. Plenty of info out there, including info on how to disconnect the solenoid, forcing full oil pressure at all times (including startup/warmup, where it might be useful). But hey, just an opinion, YMMV, etc
Junior Member
Joined: Jun 2021
Posts: 53
Likes: 10
From: Columbia, MO
2001 SL500, 2017 GLE350
I'm driving an unplugged M276. Of course, I also change my oil at 5k miles, half the interval that Mercedes specifies, or yearly, if I don't reach 5k. As I said, YMMV, do what you want. OTOH, Mercedes around me charges $360 for an A service - that's oil and filter, plus visual inspection. An oil extraction pump is $20 on Amazon.
