C350 CDI om642 correct engine temperature?

[DSM10000]

The current cold weather will have an effect and with more load from lights, screen heater, heated seats etc
My W211 with an earlier version of the engine in your car averaged around 34mpg on mixed use. I did see 43mpg brim to brim on a 200 mile journey a few times.

 

[philnewmerc]

Good point. Temperature has plummeted since the thermostat replacement...

 

[DSM10000]

Good point. Temperature has plummeted since the thermostat replacement...

Plus you may have winter diesel in the tank which has a lower energy value due to the anti waxing additives

 

[E55BOF]

Three things to bear in mind: nobody ever attains the official test figures driving normally; Mercedes will have done everything they could get away with (make up your own mind whether 'Dieselgate' was actually out-and-out cheating, or just very sharp practice...) to minimize the fuel consumption on test; fuel consumption increases in winter.

I don't think you have a problem, and on a long motorway run you might well see 40 mpg at 70-75 mph. I would have in my remapped OM642 CLS 350 if I'd ever cruised at that speed...

 

[OneForTheRoad]

Not sure if you saw my mpg photo. Glc 350 4*4 . Over 281 miles sat at 65/75 mph I averaged 40.3 at best . Sometimes on cruise control.

 

[sautah]

I don't think you are driving far enough to get a decent MPG figure reading there. My 250 CDi can take an hour or more before it starts to read over 50 MPG especially after I have used it for some short runs or it's sat unused like over Christmas when I was away for 2 weeks holiday. In these instances it hovers around 38 ish.

As far as being 6 cylinder etc I also have a BMW 6 series diesel and that gets over 50 too on a decent run. Same issue though, You have to be on a proper run before it hits the 50+ mpg Driving it for 30 minutes or so just doesn't give it a chance.

 

[Isdyl]

Hi - I've just read this very interesting thread as I'll having a similar issue with my CLS 2013 350 cdi. The temperature always sits around 70 or 75 and I've ordered a new thermostat. However, I know from previous research that the 'Diesel Emissions Software Update' which I had done a few years ago makes the engine run cooler in order to produce less NOx. I just wonder if this could be anything to do with it? Why would a thermostat have a heater element in it? Could MB have programmed the heating element to make the Stat open earlier?

 

[OneForTheRoad]

Hi - I've just read this very interesting thread as I'll having a similar issue with my CLS 2013 350 cdi. The temperature always sits around 70 or 75 and I've ordered a new thermostat. However, I know from previous research that the 'Diesel Emissions Software Update' which I had done a few years ago makes the engine run cooler in order to produce less NOx. I just wonder if this could be anything to do with it? Why would a thermostat have a heater element in it? Could MB have programmed the heating element to make the Stat open earlier?

Afaik the temperature sensor talks to the maf and glow plugs to control emissions , not the opening , that's bi metallic and a spring affair.

 

[Isdyl]

Afaik the temperature sensor talks to the maf and glow plugs to control emissions , not the opening , that's bi metallic and a spring affair.

Hi - but there is also a small heating element like a mini emersion heater within the thermostat housing. What could that possibly be for?

 

[OneForTheRoad]

Hi - but there is also a small heating element like a mini emersion heater within the thermostat housing. What could that possibly be for?

It melts a wax block I believe . Could be ECU controlled opening for winter / summer.

Every Merc diesel I've owned has ran at 90 . New and old.

 

[E55BOF]

The mini immersion heater (which is to help with emissions while the engine is warming up, I believe, though damned if I can remember how...) is often the cause of the thermostat sticking open; small amounts of crystallized antifreeze can accumulate over time in the very narrow clearance between it and it's bore in the hollow central pillar it runs through, eventually causing it to fail to open fully.

I've had many Mercedes over the past decade, diesel and petrol, and they all without exception ran at 90 degrees once the engine had warmed up.

 

[Isdyl]

I got a thermostat (pattern part from local motor factors) for £64, and paid a mobile mechanic £60 to fit it. All good now & steady at 90 degrees.

 

[ALFAitalia]

I've had many Mercedes over the past decade, diesel and petrol, and they all without exception ran at 90 degrees once the engine had warmed up

This one does too now (wifes A Class)...been getting no higher than about 60 for last few months. Not that she said until I noticed it!

 

[philnewmerc]

Update. Now the engine is getting up to full temperature, and staying there on the motorway, the brim to brim calculated MPG is.......... ***34*** exactly the same as before! (The dash exaggerates by about +5mpg so says 39).

Is this anything to do with having had the emissions update perhaps?

Is 34 mpg normal? If so I wish I'd bought a petrol . Or the 4-cylinder diesel . Oh well, it's a very quiet engine, smooth, sounds quite nice on full throttle (for a diesel), good torque etc.

....But 34 mpg on 90:10 motorway:town driving?! (70-75 mph motorway.)

I suppose it is a 3 litre turbo... But i managed to convince myself that the official figure of 47 mpg meant that in reality I'd get maybe 40 without trying too hard.

Only time the mpg improves is on long motorway runs when according to the dash readout (if i reset it once the engine is warm) it might get up to 44 mpg (assuming the 49 it shows is +5 exaggerated).

Maybe that is the crux: during my 35 minutes commute the engine is slurping fuel like an alcoholic for the first 10 minutes on warm-up then starts to be fuel efficient, but the average of those 2 stages is a very unimpressive 34 mpg.

But on the other hand the official test must have been done from cold too so.... 47???

Hmmm...

Second update for anyone interested. The air filters were absolutely filthy, black, rammed with flies and bees and leaves (apparently change at 20k miles ago by a reputable independent, not sure if that adds up but maybe). Two new air filters = no change in mpg lol!

But, whenever I floored it to the floor previously it would trigger a EML on the dash, but not now. I think at low revs the air filter resistance was low but at high air flow it was more significant and a sensor somewhere didn't like it.

Now the weather has warmed up I'm getting a bit more economy. My last tank based on longer trips for the week, was 38 mpg, which I suppose is acceptable for a car with similar torque to an AMG and is very very smooth compared to most diesels

 

[MrGreedy]

I recently changed the filters on mine, and had a resulting noticeable decrease in reported trip computer economy! Until I had a new air filter reset applied.

https://forums.mbclub.co.uk/threads/reported-economy-in-the-toilet-after-air-filter-oil-and-filter-and-winter-tyre-
change.303793/post-3444552

To save you a long read of thread derailments, if the filters are very dirty pre-change, it's worth getting an air filter adaptation reset on install of new filters. But the Merc ECU will eventually learn to work correctly with the new filters I believe.

 

[W1ghty]

Second update for anyone interested. The air filters were absolutely filthy, black, rammed with flies and bees and leaves (apparently change at 20k miles ago by a reputable independent, not sure if that adds up but maybe). Two new air filters = no change in mpg lol!

But, whenever I floored it to the floor previously it would trigger a EML on the dash, but not now. I think at low revs the air filter resistance was low but at high air flow it was more significant and a sensor somewhere didn't like it.

Now the weather has warmed up I'm getting a bit more economy. My last tank based on longer trips for the week, was 38 mpg, which I suppose is acceptable for a car with similar torque to an AMG and is very very smooth compared to most diesels

They get very dirty very quickly , I think these are 18months 10-12k miles

 

[sautah]

20 k miles is a long time to be in use for the air filters so I’m surprised you were surprised they were dirty !

You’ll never get a better mpg until you do a long drive on a motorway. 30 minutes just isn’t enough time plus the car has taught itself your driving routine running around for 30 minutes.

My 250 cdi is the same if I’ve been around the doors for a while. Once I get on a run for over a couple of hrs cruising it gets back to its usual 50 plus mpg

 

[OneForTheRoad]

They get very dirty very quickly , I think these are 18months 10-12k miles
View attachment 168805

The new style filters stay surprisingly cleaner for some reason. Could be the areas we live in I suppose. Saying that my e350 came from Scotland and my glc from Cheshire. Both sets were pretty clean after 20k + miles.

 

[W1ghty]

20 k miles is a long time to be in use for the air filters so I’m surprised you were surprised they were dirty !

You’ll never get a better mpg until you do a long drive on a motorway. 30 minutes just isn’t enough time plus the car has taught itself your driving routine running around for 30 minutes.

My 250 cdi is the same if I’ve been around the doors for a while. Once I get on a run for over a couple of hrs cruising it gets back to its usual 50 plus mpg

The manufacturers change is 40k miles , maybe that’s why he is surprised ?

 

[CyShroff]

It is not normal, I promise. Once warmed up it should be sat at about 89C, just under 90 and should stay there regardless of the situation.

I went through this too, people saying this and that. Changed it and realised that it was all nonsense and should be ~90 rock solid and stay there once warmed up.

That's my experience too -- 90° when wwarmed up and stays at 90 regardless of driving situation. I average 40 to 45mpg on motorways and in London barely get more than 20mpg. It's an 8 year old OM642 engine in a e350d Estate (S213)