Hi All,

I have a 66-plate W205 - I got a CEL around 3-4 weeks ago, and car started running cold.

Engine temp below coolant regulating temp..
Symptoms were akin to the thermostat being stuck open 100% of the time, oil temps barely reaching 70C
- Usually when driving around in eco, oil temps are around 89/95 max

So I decided to buy a new thermostat and replace the old failed one.

After replacing everything and topping up the coolant reservoir (it only dropped a tiny bit)

I started the car up, no leaks, coolant temps rose and steadied out as normal.
The oil temps rose just as they used to, nice and quickly now - But the oil temp is now sitting around 99/100C during normal driving?

If I drive it hard the oil temp rises to around 103 but drops back down to 99 or so fairly quickly.

Coolant temps are indicating as perfectly normal and no different to before the original fault.

Do the springs on new thermostats take time to bed in?
Could it be less travel on the valve stem or something like that? All the hoses are hot and I’m getting heat in the cabin.

The oil temps do come down quickly which is a relief, but the elevated average temp is a slight concern right now.

Any pointers chaps?

Interesting. I would have to check the part numbers etc because what you are describing is the behaviour of my vehicle with the factory thermostat, 2017, so I wonder if perhaps the part numbers of changed and at some point you had a lower temp thermostat? Did you buy the car used? Perhaps they had installed a lower temp thermostat?

I am not sure of these things. I would need to look into it. But as of right now it seems to run as mine does, if that is any comfort.

Thanks for the reply, that does make me feel better.

This is what I fitted:

Quinton Hazell Coolant Thermostat QTH1114K

After a few days of driving it’s still settling and fluctuating between 97-100 in Efficiency.

Now I’ve had the chance to push it into Sport+ the temps rose to about 104 but came back down to 100 pretty much straight after, and the coolant temp didn’t seem to budge at all, which boosted my confidence in the new thermostat.

Before I switched to the C43, I had an S5 and that always ran at around 95-99 degrees with a very similar engine, so I know the oil temps in that range aren’t normally a problem.

My main worry was that I didn’t know if our engine should be running a bit cooler, and also because I’d done the repair myself haha.

Everywhere I’ve researched since indicate that 95-100 is where it should be at - So I think I can let this go. Always happy for more input though.

Yup agree, those values that OP now have are the operating temperatures that I see on my car, also a 2017.

The opening temp for that thermostat is 103 deg C. I guess good job on the repair! Seems like you’re in the clear, haha.

In my vehicle, since I changed the water cooler, I have noticed irregularities in the working temperatures. I have changed the thermostat but it remains the same. When I drive aggressively and I return to calm, the car's oil temperature drops quite a bit and the coolant temperature drops a bit. normal, after a while it stabilizes again, the car drives me crazy

Hey, do you know why this happened? Is this normal?

Did you actually ended up changing the thermostat?

No sir. I took the car to mercedes, they said everything is operating as it should. Apparently the m276 biturbo has no oil cooler thermostat, so the oil is being cooled constantly. The reason i am bothered is because i live in texas it was 85F outside and i was driving spiritedly in sport plus and reached an oil temp of 232F. Last night I think after i got off the highway with some spirited driving in sport plus my oil temp went from 216 to 178. It was 50 degrees farenheit. I am so lost. I don’t know if my oil temp going down to 179 from 216 is safe or not. But the mercedes techs are saying everything is working as it should

232F is on the high side but you said you are tuned right? Perhaps you coolant pump was turning on more and higher when it went from 216 to 179.

What engine oil do you use? 5W-40 or 0W-40?

Here is a little coolant pump mod you could consider: https://mbworld.org/forums/c450-c43-...ic-pump-4.html

No sir i am not tuned.

i’m not sure, but whatever is rated for the car should be in it. I haven’t gotten to an oil change yet i just got the car 2 months back.

I guess it was another forum member. You have an E 43 though, with more creature comforts that might also stress the engine a little bit more than a C 43 as more things to run, more systems specifically. I wonder if it is normal for your reason.

For what it's worth, with long continuous driving across Australia - a few days of 9hrs+, ~110km/h, my oil sat around 90-92c and coolant 82/84c. M276 2018 facelift C43 coupe, 47k km. This was across Australia with outside daytime temperatures varying between 26c through to 38c. It had 5W-30 in it (which I have changed to MB 5W-40). Cheers

Wow that is very low, North American cars usually goes up to 100c for example, all of my friend's cars go up to 96 C on the highway, mines also around that mark, the lowest when at operating temperature, it usually hovers at 95 for me on the highway. I wonder if regulations has to do with it, I am using motul xcess gen 2. I have all the latest updates TCU and ECU and powertrain control unit updates, I have 2017.