I recently bought a W212 E350 with 100k miles to replace a previous one that was written off after someone crashed into it.

The replacement is in great nick in general and has a full service history but the engine does not seem as strong as my previous car. I drove 30k miles in the previous one, which had done 130k miles by the time it was written off so I knew it pretty well. I did test drive the "new" car before buying it but it's hard to tell subtle things when you're driving someone else's car for a shortish drive.

The specific issues are that it's quite a bit noisier under load than my last car - it sounds a bit more like a typical diesel engine than me last one. It sounds the same when not under load (ie not going steeply uphill or accelerating). The top end feels a bit weak (3500 rpm and up) and it stutters briefly while accelerating typically on a part throttle at about 1500-2000 rpm. In general it pulls strongly and the fuel economy is similar to my last E350.

I suspected that the previous owner had run it on the cheapest diesel he could find so I ran a couple of tanks of V-Power diesel through it and also tried a bottle of Wynn's Diesel System Cleaner (it was called something like that). That definitely helped and it now pulls strongly at low revs.

I shall be taking it to a garage in due course to see whether they can find the issue but I thought I'd ask here first.

What should I be looking at in the case of symptoms like these? Any suggestions would be warmly welcomed.

 

I wonder if engine and transmission mounts are the culprits. In my case, it was the transmission mount that needed to be replaced. These mount are known to fail on the W212.

 

I would consider fuel filter and the exhaust pressure sensor then deal with glow-plugs.

 

Check diesel particulate filter (DPF) and exhaust particulate matter sensor
Both are critical to reducing emissions and ensuring the engine runs efficiently
Search for how to clean, running the car some distance is one way
Don't have an oil burner myself

 

That is something I hadn't considered. I'll see whether I can tell and if not, mention it to the garage when I take it in.

 

The fuel filter was something I had thought of. Do you know whether it's simple to replace or is that a garage job? I have had DPF pressure sensor issues on my previous E350 but that caused it to go into limp mode which it so far hasn't. I'll have to look into the glow plugs. I'm only dimly aware of what they are let alone what problems they may cause.

Thank you.