350 Cdi Coupe 2009 106k - Overheating - Newbie - devastated - UPDATE & Info

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May 24, 2023
Mercedes E350 Cdi Coupe 2008/9
Hi, I purchased the car yesterday, and thanks to other forum members I sorted the tyre pressure issue, the car felt great. On my 30 mile journey tonight there was a lot of stop start on the way there, but car was running fine. On the way home the Temp Warning came on the dashboard and I could see steam from drivers side corner of the car. I managed to stop fairly quickly, the expansion tank was nuclear hot, after sometime I was able to loosen enough to allow the burbling water out, I left it for another ten minutes or so and added maybe a 1/2 litre of water. On ignition temp showed as halfway, I stuck on the heater full blast and drove another 5 miles till home, during this the temp gauge stayed fairly in the middle with the occasional rise and fall. At home on idle the car was sitting at correct temp, but if I revved it rose sharply once.
When I first stopped I could see no water/coolant under car.

Any advice on what to do next would be much appreciated, I have a very limited budget which I know is not good for this type of car, but it seemed right. Please feel free to come up with any ideas or solutions, I am not a mechanic but can follow a plan.

Many Thanks and fingers crossed.
Hi, apologies I couldn't see how to update my previous post. I have an AP200 Bluetooth Scanner that I used on my Jeep which had a Mercedes engine, I realise it's basic but thought I would see if this helps nail the problem or rule out some. The car is restricted to 3000rpm, the scanner cleared the Check engine Light, it also through up a lot of stored codes, but no direct mention of the thermostat. The code I cannot clear is 10BF00 - Component M4/7 (combustion engine and A/C with integrated control fan motor) has an open circuit.
Could this till be related to a faulty Thermostat? or is this an entirely different issue, interestingly today leaving the car on idle it did not over heat, no matter air con heat or cold. The fan at radiator never started.
I have looked at videos for the changing of Thermostat, they all seem to involve moving serpentine belt, but looking at the engine today it looks like the thermostat is at the top of my engine and accessible even for me, I have attached an image for conformation. Checked oil and coolant no mayonnaise.
I have a thermostat on order as I struggled to find a garage locally due to the bank holiday etc, would changing the Thermostat myself, be a good move, so that if it is not that then a garage could rule that out.
Many Thanks for all the previous responses, I know cars go wrong, and I know these are expensive to maintain, so I do appreciate the assistance.

Cheers Gordon


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I did it not long ago on my E class ….got it from Autodoc for £34 delivered . It’s not an MB one , but it’s the same make as the current fitted one .
Straightforward , 3 bolts, easy access . I jacked the car up on the opposite side to the coolant tank so only lost a few teaspoons of coolant . Bolts torqued to 8nm
It probably to an hour in the sun .
Testing the old one , it is jammed open , no movement at all when putting it in boiling water .
Thank you.

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