Tannpirker

Hi, I just picked up a 2010 C200 CDI Blue efficiency with 230 000 kilometers on it. For a couple of days everything worked fine, but today the fan kicked in (very loud) and the temp gauge was in the red. City driving below 45mph. I also connected Obd2 and it showed coolant temp at 118° Celsius. What is weird is there is no smell( like typical overheating) and the high temp light never came on, no beeps or anything. Expansion tank not releasing high pressure (just a small burp) and both engine, expansion tank and coolant lines normal temp it seems like. Nothing crazy hot in there.

In conclusion I don't think it is actually overheating. I'm thinking a shut thermostat or a bad sensor, but I mainly worked on Japanese cars in the past. Hoping for some input here.
Thanks in advance.

bv9900

It's a sensitive topic, it's probably nothing, but save evidence if it happens again and constantly keep an eye on the clock. Notify the seller and inform him of the message in the forum, if he is concerned he will know how to advise you. If you are concerned and responsible, since it is a recently concluded sale, I would change the pump and the thermostat, and monitor the internal state of the circuit when removing the thermostat. It is just a precaution that the car falls into a more serious problem such as a head gasket. If it were a sensor...it would be discovered later, without a lack of cooling that could lead to a catastrophe.

JettaRed

iTrader: (1)

First, don't take any chances until you are absolutely sure the car is not overheating. Get a Mercedes-specific scan tool and throw the generic OBD scanner away (or keep it for your Japanese cars). Generic scanners can provide incomplete, incorrect, or otherwise misleading information. Any codes you get, cross reference them to Mercedes DTCs.

2nd, you DO NOT want to wait until you smell coolant. A stuck thermostat CAN cause overheating.

With a proper scanner, if the temp sensor is bad, you will likely have a code. I am not familiar with your engine, but the temp sensor is probably easy to change out.

Here's a very good scanner to have. About $160 on Amazon, but don't wait, they sell out fast. (It will cost you about that much to have a shop scan for codes, as well.)

Tannpirker

Thank you guys for input. The car will not drive until i get this sorted out, that's for sure. I now went out and checked the temp(with my generic obd) and it said 138°Celsius(!). Located the temp sensor and i could touch its base no problem, guessing about 55°Celsius.

Im going to order a new sensor, and a suitable scanner.

TimC300

118 C is overheating. The thermostat is designed to open at 100 C (212 F). On my dash the temp appears to hover around 90 C, I never see it go above 100 C.

I would start the car and let it run, watch the temp gauge when it climbs past 80 C, what does it do? If it just keeps climbing I would change the thermostat.

Im not sure what engine you have. I have the M272 and the Mercedes thermostat is made by Wahler, its stamped on it. May save money just buying the Wahler brand instead of over paying for Mercedes.

JettaRed

iTrader: (1)

138°C is high. My normal temp is around 93°C (198°F). 138°C would be uncomfortable to touch. I would replace the temp sensor first.

A while back, VW/Audi had a bad batch of temp sensors that would report low temps. I always kept a couple on hand. I've not heard about Mercedes having bad temp sensors, but they must fail at some point, otherwise why sell them? Your car is 14 years old, so maybe it is a bad sensor. That would be the cheapest and easiest to replace first.

Tannpirker

I hope this is it, gonna order the thermostat too, so I have it if it turns out the sensor is good and thermostat sending coolant on a short, hot loop.

Thanks you guys, I really appreciate it!

Tannpirker

So i called a friend of mine, he instructed to simply pop off the top hose between the thermostat and radiator. If stuck close, it's dry. And it indeed was!

JettaRed

iTrader: (1)

Is the temperature sensor on the radiator or the engine?

JettaRed

iTrader: (1)

So, it appears that the temperature sensor is on the thermostat housing. If the thermostat is stuck, that could contribute to the bad readings. But if it is stuck closed (i.e., isolating the radiator) that could be very bad. I just can't tell from the picture if it is stuck. Below #80 is the t-stat housing and #90 is the temperature sensor.

Tannpirker

I was under the assumption the electronics on the thermostat housing were diagnostic. The sensor on the back of engine(top, see picture) is a coolant temperature sensor too. This is the one I ordered. There is alot going on with this engine in regards to electronics and sensors and I find it all a bit confusing.

I am going to investigate further, new parts not arriving for a week but I plan to test the thermostat with boiling water and maybe rent a mb scan tool to get a clearer picture for now.

Worst case scenario thermostat is stuck closed and the horribly high readings were correct. Not a religious man but might say a prayer on this one.

JettaRed

iTrader: (1)

Here you go. Spend the money and get your own Mercedes scanner. You WILL use it often. It not only scans for codes, but you can also view live data and make some configuration changes. Make sure to use the coupon.

Tannpirker

Thanks for sharing. I will get a proper tool from a physical store at a later time.

Tannpirker

Just a little update. With the engine cold(16 hours not used) the temp still shows as 118°Celsius. When i unplug the sensor it shows -40°Celsius. So i guess i found my culprit. Sensor is the one in thermostat housing