MBenzo250_

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.

kajtek1

There is no way the engine shut down at 80C and park for 1 hr can have 120C on restart.
It has to be electronic glitch.
Sounds like you have no scanner, so it is good time to get one. This way you can read if the ECU can see the same temperature the cluster shows.
Anyway, each time you have troubles, it is good idea to start with basics.
Replace air filter, replace fuel filter, double check coolant level and coolant clarity.
Check the wringing coming from temp sensor and wash the plugs with MAF or electronic cleaner.

MBenzo250_

Thanks for your reply.
Yes i forgot to mention i did get a service a week before this started happening (Probably not related to it)
Air Filter,Fuel Filter changed and Coolant was topped up.
I am starting to think its a electronic glitch too! Before i do take it back to MB Dealership do you think it could be air pockets in the cooling system by any chance?

kajtek1

I did say "double check coolant level" didn't I ?

Arrie

I would be checking the coolant level n the radiator and not trust the reservoir level. Your car acts like low coolant, very low.

When you drive the water pump circulates the coolant even when low level but when you shut the engine off coolant drops in the bottom and if level goes below the temperature sensor the temperature at the sensor can go very high like when you shut the far off and then start it. I’m not sure it would be 120 degrees after an hour though.

I experienced this problem in the past when I lost almost all coolant but the reservoir was at correct mark. This was a Chevy Tahoe. I know we don’t talk about a Chevy here but the symptoms point to very low coolant level and if it was correctly filled when the thermostat was worked on and goes low in just a few weeks you have a serious engine internal coolant leak issue unless you can see coolant leaking under your car.

Is is it still under warranty?

MBenzo250_

Hi thanks for the quick reply. I will have to check to see if coolant is actually going to the radiator. Regarding the waterpump MB dealer has said its fine as they checked this.
I will keep you updated on what they say.
Meanwhile Iv tried to attach a video however it wont allow me, so heres a picture

As i turn the key once, before starting. Then after 20 seconds its goes down steadily.

Arrie

So it goes down before you start the car? If that is the case then it is electrical. Did anybody think of replacing the temperature sensor?

MBenzo250_

So when it shoots up it will come down slowly yes, Even if i start the car it will stick at 120 and come down slowly. Only issue is once its reached operating temperature during driving it will go in limp mode, and sometimes the engine will cut out.
Temperature sensor has been replaced when the coolant housing and thermostat housing was done.

kajtek1

What are the codes?

MBenzo250_

Worst part is that there are no fault codes showing. Checked by two independent garages and also at MB dealership using the star diagnostic nothing codes are thrown.

kajtek1

When there is a limp, it has to be a code.
Now is good time to get your own scanner, so you can read codes when they happen.

Arrie

So, to make it clear. When you go to the car and the temperature is high does it come slowly down BEFORE you start the engine, i.e. if you turn the power ON without starting the engine?

MBenzo250_

Yes thats correct when i turn the key once (cars not started at this point) the temprature shoots up then slowly declines. However if i the turn the engine on it does the same thing shoots up and slowly declines to operating temperature. Whilst driving it will overheat but i suspect this is whats causing the limp mode as soon as park up it shows its over heating.

Arrie

Another question: If you put your climate temp setting up to HI HEAT does it blow hot out the vents? This after engine is at normal or over heating temperature.

MBenzo250_

Hi yes i have tried this and it still blows hot air out of the vents. I thought it may of been bad a head gasket previously too.

Arrie

Has MB looked at the water pump?

MBenzo250_

..

MBenzo250_

The issue seems to be solved. It was down to a faulty Oil temperature sensor within the Oil Sump. So far so good!
Thanks everyone for their help.

S-Prihadi

Oil Temp Sensor ? and not Coolant Temp Sensor ?
This is like saying the Coolant Temp Meter on the dash also somehow get data input from the Oil Temp Sensor too ...for that 20 seconds after engine start where you get 120 C reading.
Oil temp is usually 10-20C higher than coolant temp at normal cruising operation.
This is unique ....
.

Mud

Very interesting, I wasn't even aware there was an oil temp sensor.
If this is the case my guess is that the ECU correlates oil and coolant temperatures, allowing for a slight variation range between the two. If one or the other is reading out of range the ECU may trigger the temp gauge as an indicator.
I'm curious enough to look in the WIS later to see if wiring diagram indicates anything....
Also, oil temp can vary from about equal to slightly above coolant temp - larger sump capacity and an oil cooler usually yields lower oil temp. Only way to verify in this case is to use diagnostics to see what oil and coolant sensors are actually reading during operation.

S-Prihadi

Yes please, I am curious too .

nickki23

Hi I’m having the same issues with my car did they ever figure out what was wrong?