W204 CDI Coolant Temp Fluctuating

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ealp

Member
Joined
Oct 1, 2012
Messages
38
Car
2014 w204
Hi I have a 2014 C250 CDI. The temp normally stays around the 87-90C mark.

However recently its been getting to that mark, and after about 40 minutes of driving it'll slowly drop to 75-80c mark, then slowly raise back to where it was. This happens on almost every journey now, sometimes multiple times depending how long the journey is. It can be at high speed or low speed, so its not dependant on engine load.

An idea what this could be?
 
Thermostat stuck? not opening and closing according to actual temperature, i.e. stuck open letting more water through causing cooler fluid.
This is only a guess though.
 
Thermostat stuck? not opening and closing according to actual temperature, i.e. stuck open letting more water through causing cooler fluid.
This is only a guess though.
As Eddie...Thermostat is a common problem on these.

Ernie
 
had the same problem with mine and was the thermostat
 
Has similar on a five series BM- bled the coolant of air, changed the thermostat and then found the root cause which was the water pump on its way our. It wasn't circulating enough water in traffic, hence temp going up in slow traffic and down when moving quicker.
 
Had thermostat replaced under warranty a couple of weeks back as well. Temp would go up and down but never even get to 80. All good now.
 
Had the Thermostat replaced under warranty but still the same. Sounds like it could be the water pump then.... I will report back once I know the root cause
 
Looks like the sensor on the left. I take it that it'll be fixed under warranty? It will be interesting to hear what the problem is, what mileage has it done?
 
Yes its under warranty. Its done about 57K. I will keep you posted :)
 
I know the temp sensor is separate on mine, but it is a different engine. In regards to that one, what I was told was that if it is the sensor that has failed it will read completely cold or it will max out as if it were overheating. That is as soon as you start the key.

Water pump is all that is left in regards to controlling the system in the car. Of the warranty pays out then worth a shot.
 
So I've had the thermostat and water pump replaced under warranty. However still the same behaviour. I can be driving normally for ages and it'll stay at 90c. Then occasionally it'll drop down to 75-80C, then it'll rise back to 90C (all within about 1-2 minutes) then it'll stay at 90 for another 30 mins or so. If anyone has a W204 with the C220/C250 CDI engine, I'd love to know if this is the same for you while driving...... I'm sure its doing no harm, and just something I'll have to live with now, as I'm fed up going back to the dealers
 
My coolant temp. occasionally fluctuates as you describe......this is even after replacing the thermostat with a MB part complete with new thermocouple.
I am just going to live with it.
Tony
 
So I've had the thermostat and water pump replaced under warranty. However still the same behaviour. I can be driving normally for ages and it'll stay at 90c. Then occasionally it'll drop down to 75-80C, then it'll rise back to 90C (all within about 1-2 minutes) then it'll stay at 90 for another 30 mins or so. If anyone has a W204 with the C220/C250 CDI engine, I'd love to know if this is the same for you while driving...... I'm sure its doing no harm, and just something I'll have to live with now, as I'm fed up going back to the dealers

Yup as above I just went through the same issue and MB replaced the Thermostat under warranty, it is a 2013 C250CDI. All the same symptoms as you with fluctuating coolant temps. Also taking forever to warm up!
 
i have the same on my e350 cdi. temp was always stable at below 90 degrees, now wanders between below 80-90
 

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