Mercedes E250 W212 Coolant and Overheating issue

[Mbenzo]

Hi, Apologies i am new to MBWorld Forum, Hopefully i am posting in the correct area.
I have a Mercedes E250CDI W212 Coupe, however recently i have started to get a strange issue with the engine temperature gauge and coolant light.

As a example if i drive the car for a around 10 minutes and park up (Parking up for a hour for example). When i return and turn the key to start the engine the engine temperature gauge seems to be shooting up to 120 degrees, then slowly starts to drop down to around the 85 mark to where it should be. Often if im unlucky gauge displays past 120 degrees mark along with a red warning on dashboard "Coolant Warning Switch Engine Off". At this point the fans kick in and seem to be quite loud until eventually it cools down again.

The issue i am having is the car seems to go into limp mode and thinks it is over heating when it is not whilst im driving, and a few times the car has switched off on me whilst driving on a busy road. First power steering goes, and the car automatically slows down followed by the engine switching off on me.Whilst the fans are turning on high speed, I can turn the car back on again but the engine temp will show 120 degrees.

So i visited my local Mercedes dealership in the east midlands whom then hooked it up the star diagnosis machine. They found it was flagging two issues up and they advised me to replace Thermostat housing(due to there being a crack) and Coolant housing (as there was a leak). So i got these replaced and Mercedes mechanic tested it by taking it for a short drive all seemed fine.

So its been roughly 3 days, and just my luck just about to turn engine on, temp gauge went back to 120 Degrees then declining again followed by the car going into limp mode after driving for 5 minutes.

So i did take it back to the dealership who hooked it back to the Star Diagnostic and said there was no fault codes or anything. I decided to leave my car there for a couple days as one of the mechanics luckily said he will sit in the passenger to see exactly what was happening whilst driving. TYPICAL we drove 20 miles and car was fine no incorrect temp readings, no limp mode and was picking up as its supposed to.

A couple of days later i start my engine early morning ready for work, and the dashboard warning started to show "Check Coolant Level". Checked the coolant level by checking the reservoir and it all seemed fine. On the way to work whilst driving i could feel the car going into limp mode after driving for around 15 minutes again!, and once i got to work switching the engine off and on again showing 120 degrees!

I am clueless to what this could be, and hoping anyone could help?

Few Points:

- The car never shows its overheating whilst driving as the temp stays around the 80 mark. (only after parking up, taking key out and putting back in after 5 minutes it may show its over heating at 120 ( even though MB believe its not)
-There was a coolant leak previously however now thermostat housing and coolant housing have been fixed and there are no leaks
-MB have diagnosed with no error codes showing now
-Coolant Reservoir is topped to exactly where it should be
-No other dashboard lights
-MB have given me a full report of everything has been checked over and it seems fine to them.

I can attach images later, possibly a video.

 

[CowleyStJames]

I'm not an expert but I'm thinking temperature sender perhaps?
If it's faulty, surely you could get the symptoms you're describing, or perhaps an air lock in the cooling system

 

[Mbenzo]

The issue has been solved (touch wood) seemed to have been fault oil temperature sensor in the oil sump which was shorting. That has been replaced and seems to be ok so far.

 

[Kcl]

2013 Mercedes E-Class E250 (Petrol). Dashboard Temperature Indicator Signalling Possible Fault
In last 6 weeks, I experienced a couple of incidents of Temperature Indiator reaching 120C within 10 minutes of start-up (after ~1 hr shut down) and speeding up on a motorway; in one incident the dash board messaged to stop and shut/cool down engine. I stopped, switched off engine to reset and then started up within half minute, and the car ran fine after.

Lately I noticed dashboard Temperature Indictor would warmed up gradually to 90C. However when stopped at traffic light the temperature visibly dropped slightly. It also dropped from 90C (where it had stabilised) down to 80C (or even 70C) when I sped up/tested on motorway (cold winter), before it increased to re-stabilise at 90C. If I slow down and then speed up again, the temperature would fluctuate the same again.

• I don’t know if the above temperature fluctuation (according to driving condition) is normal
• I don’t know whether if temperature drop (on speeding up) was due to extra cold wet air on the radiator. The temperature needle was responding/moving a lot according to driving condition; the movements seemed more abrupt rather than gradual. Surely frequent fluctuations from stabilised 90C down to 70C cannot be good for the engine/radiator system - thermal expanson/contraction stresses?

I have a garage to replace my Thermostat (which comes with temperature sensor fitted). The temperature fluctuation remains the same. I have not yet re-experienced any 120C incident, but the car has only been back 1 day so far.

Please - any comments anyone. I saw one past report that the Temperature problem could be due to “Engine OIL TEMPERATURE SENSOR” failure/shorting-out. Shall I change the Oil Temperataure sensor to see? I hate to spend more if it is not necessary.

 

[Uky]

(This may not apply to your engine), but for the M/Y 2009 4-cylinder in-line CGI engine, the thermostat had both a temperature sensor and a heating resistor for temperature control.
Those thermostats had a quality problem: A rubber gasket inside the thermostat was prone to loosen and blocking normal functionality resulting in a constantly open valve. This results
in coolant flowing to the radiator regardless of engine temperature. This resulted in the indicated engine temperature readings fluctuated - a lot!

Easy to check: Cold-start the car and drive a mile or two. Stop the car, open the hood and grip the outgoing
hose. If the hose is luke warm: Faulty thermostat. If the hose is cold: OK.

I replaced my thermostat myself. It was a 1 hour job. My car had the low pressure turbo fitted. Almost suffered a stroke trying to remove
the plastic air hose that was blocking the access to the thermostat. The rest was easy.

 

[Kcl]

Thank you for your E-250 comments. Much appreciated another point of view.

My thermostat (fitted with temp sensor) has been replaced with Mercedes parts; BUT the fluctuation still continuing.

I begin to wonder what is the typical behaviour of the Temperature Indicator of a 4 cylinder E-250. (My wife C-280 6cylinder engine has her Temp Indicator rock steady at 90 for all driving conditions once the temperature stabilised to 90C). I wonder if my 4-cylinder E250's temp indicator is meant to fluctuate - though I doubt so, because such frequent big deviation (70-90C) is likely to cause thermal stresses

 

[geoffus]

Thank you for your E-250 comments. Much appreciated another point of view.

My thermostat (fitted with temp sensor) has been replaced with Mercedes parts; BUT the fluctuation still continuing.

I begin to wonder what is the typical behaviour of the Temperature Indicator of a 4 cylinder E-250. (My wife C-280 6cylinder engine has her Temp Indicator rock steady at 90 for all driving conditions once the temperature stabilised to 90C). I wonder if my 4-cylinder E250's temp indicator is meant to fluctuate - though I doubt so, because such frequent big deviation (70-90C) is likely to cause thermal stresses

My 2014 E250 does not fluctuate, it rises slowly to around 90 and stays there, maybe dropping a degree or two but that's it. if that's any help ?

 

[Kcl]

Yes yes it helps - thank you. Feedback from another E250 is very useful.

I may have to try changing the Oil Temp Sensor (as expereinced by the other MERC driver) to see if it helps. I think my pump and belt etc are ok - as they responding well; and I have no frequent temp overshoots (above 90C) other than the two earlier incidents of 120C before my "thermostat/coolant sensor" change. My temp fluctuation shows something is still not right - if other E250 holds the temp well. I think it is some thing/sensor etc triggering the computer to open/close thermostat in such manner to cause temp fluctuation.