GLS550 running rough…and smooth?
Thread Starter
Super Member
Joined: Oct 2017
Posts: 699
Likes: 149
2015 SL550, 2017 GLS 550, 2010 G550, 1995 E320 Cabriolet
GLS550 running rough…and smooth?
Two nights ago I added some Liqui-Molly Ceratec to my GLS. At first, I was shocked with how well it worked. Over the course of 30 seconds I could feel the engine become dramatically smoother. I made a short drive on Christmas Day and the engine was running much, much better.
Today, the car is running rough at idle (600 RPM). Two interesting things to note. When I put the car in reverse, RPMs fall to 500 (without any throttle input, foot on brake) and the engine smooths out quite a bit. Any speed between 800 and 2500 is similarly very, very smooth - I haven’t gotten the engine over 2500RPM so far - lmost no vibration whatsoever.
Im at a loss as to what to think. I’m not sure the engine mount diagnosis I got from the dealership is valid - I don’t think the mounts would lead to reduced vibrations at higher and lower RPMs (unless there is some weird harmonics issue at play). I placed my hand on the idling motor and it felt just about as rough as it does from inside the car. Again, that wouldn’t lead me to believe that mounts are the problem.
The GLS has 42k, has been driven very, very gently, is always kept in a temperature controlled garage (maintained at 55F in the winter), has experienced very few cold starts, etc.
Today, the car is running rough at idle (600 RPM). Two interesting things to note. When I put the car in reverse, RPMs fall to 500 (without any throttle input, foot on brake) and the engine smooths out quite a bit. Any speed between 800 and 2500 is similarly very, very smooth - I haven’t gotten the engine over 2500RPM so far - lmost no vibration whatsoever.
Im at a loss as to what to think. I’m not sure the engine mount diagnosis I got from the dealership is valid - I don’t think the mounts would lead to reduced vibrations at higher and lower RPMs (unless there is some weird harmonics issue at play). I placed my hand on the idling motor and it felt just about as rough as it does from inside the car. Again, that wouldn’t lead me to believe that mounts are the problem.
The GLS has 42k, has been driven very, very gently, is always kept in a temperature controlled garage (maintained at 55F in the winter), has experienced very few cold starts, etc.
Last edited by JD101b; Dec 26, 2024 at 07:32 PM. Reason: Grammatical issues
Out Of Control!!
Joined: Sep 2018
Posts: 14,692
Likes: 4,584
From: unbegrenzt
2017 GLE350 4MATIC
Don't ignore advice. Higher engine speed reduces the sensation of all vibration. Your description is consistent with, among other things, bad mounts or mounts on their way out.
Scan codes and post them here.
Please give a full rundown on this car:
miles
how long you have owned it
services done in the past 12 months
list of codes
Scan codes and post them here.
Please give a full rundown on this car:
miles
how long you have owned it
services done in the past 12 months
list of codes
Thread Starter
Super Member
Joined: Oct 2017
Posts: 699
Likes: 149
2015 SL550, 2017 GLS 550, 2010 G550, 1995 E320 Cabriolet
Don't ignore advice. Higher engine speed reduces the sensation of all vibration. Your description is consistent with, among other things, bad mounts or mounts on their way out.
Scan codes and post them here.
Please give a full rundown on this car:
miles
how long you have owned it
services done in the past 12 months
list of codes
Scan codes and post them here.
Please give a full rundown on this car:
miles
how long you have owned it
services done in the past 12 months
list of codes
Cheers!
