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2015 C300 4Matic
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12 Posts
Discussion Starter · #1 ·
I'm having overheating issues and I can't find anything online or on any forums. I hardly ever take the freeway and mostly drive around town because I work at home. Today, I was starting a 100 mile trip to Bullhead City, AZ and after a few minutes of driving on the freeway at 70 miles per hour, the temperature gauge quickly went in the red. I immediately pulled over to the side of the road, let the car cool down, then got off the freeway and took the surface streets back home. It didn't go back in the red at all while I was driving the 45 mph speed limit or idling at any stoplights and the temperature stayed at around the 80-90 mark. When I got home, I saw that the fan was running before and after I shut off the engine. An hour later, I checked the coolant level and it was normal. There were no codes thrown after running a scan. I did notice that there is a very small coolant leak (picture #1) so I'm thinking that it has a bad gasket and it seems that the thermostat is stuck on closed. I located the thermostat assembly (picture #2) on the FCP Euro website and the assembly and the 4 gaskets go for about $170 plus tax and shipping. The thermostat assembly looks a lot different than the one in the previous model year that my brother has and it definitely looks more complicated to swap out due to it's location under the silver box in the engine bay (picture #3). Has anyone changed the thermostat on their W205 yet? I am just shy of 28k on the odometer and I didn't expect to have this replaced so soon. The connections at the top of the silver box (picture #4) look manageable with the clip on the left, a bolt or 2 at the top, and the sensors on the right that need to be disconnected. I'm not sure how to remove the clips in picture #5. If you remove the clips, do you need to replace them with new ones? And on the bottom right of the silver box, once you pry off the plastic clips on the 2 metal lines in picture #6, how do you disconnect them from the plastic connectors that they are attached to? The sensor to the left of the metal lines can be easily pulled off of it's plastic holder. Is it possible to just free up the top part of the silver box and swivel it out of the way to get access to the thermostat assembly? Any advice would be greatly appreciated so that I can avoid going to the dealership. The local mechanics here charge almost as much so I don't go there either.

I drove around town a few hours later to run some errands and this time it started going into the red at around 40-50. It's really frustrating that I haven't been able to find anything online so far. Does anyone have a DIY on replacing the thermostat assembly?
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2015 C300 4Matic
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12 Posts
Discussion Starter · #2 ·
Update: the silver box is actually called a Charge Air Inter-Cooler Radiator which is what I asked for with assistance in removing so that I could get access to replace the thermostat assembly located underneath. I lucked out and ordered the genuine Mercedes part from FCP Euro which normally goes for $175.00 but was on sale for $40.00 off. The 4 gaskets cost $3.59 each though. There was a delay in the shipping so they credited me $37.00 for all shipping fees. They were even thoughtful enough to send me the diagrams for the Inter-Cooler Radiator, Water Pump, and Thermostat Assembly so that I can easily identify all the parts and easily disassemble/reassemble everything. Their parts also have a lifetime warranty which is awesome.

I posted my question 8 days ago and didn't get a single reply from anyone here. I posted the same question on MBWorld and instead received a non-answer. A "Super Member" responded: "Take it to the dealer. You will probably end up there anyway. Why wait. Seems like you're going in circles". Really? What a jerk answer that was. BTW, the dealership quoted me $550.00 plus tax for the parts and 3.5 hours worth of labor.
 

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2000 CLK430 Cabriolet 130K W208
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4 Posts
I have a 2000 CLK430 which started to run hot recently. Summers in Tucson are hot so a little above normal is to be expected. I've noticed a coupla incremental increases in the temp gauge last couple of weeks...and at the same time some rough shifting and slipping in the transmission. Pretty sure the running hot and Tx problem are related; the Tx has no issues when starting out cool. My Thermostat looks a whole lot easier to change-out than yours! Yes...you gotta love the clowns that lack any confidence in any repair except those done by the dealer. I use this site for the express purpose of avoiding the dealer....
 

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2015 C300 4Matic
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12 Posts
Discussion Starter · #4 ·
I'm still working on replacing the thermostat. I ran into a problem today with trying to remove the 2 bottom torx scews on the charge air intercooler on top of the thermostat. There's no clearance for the bottom torx screws but I found a set of offset torx keys at O'Reilly's that have a 45 degree angle on one end. They come with a coating on them that let's you grip them better and avoid dropping it into the engine somewhere but It takes forever to unscrew them cause you can only turn them a quarter turn at a time since the screws are about 5 inches long and after you loosen them you can't pull them out cause they're so dang long and have to just let them hang in there until you pull the whole unit out. Next I unplugged all the sensors then realized I had to unplug the ECU too which fortunately you can move out of the way just to find out that there is another screw on the right of the intercooler which uses an E socket. There is not enough clearance for my long sockets so I have to get some shorter ones. I also broke one of the 2 hose clamps that connect the intake pipe to the intercooler but luckily I have some spare 3 inch hose clamps that are a lot better quality than the Mercedes ones. You have to remove the intake pipe to get to the screws in the front of the intercooler which are e-scews. I ended up connecting everything back up so that I can drive somewhere tomorrow and get some shorties. I just can't drive too far or take the freeway cause that's when it overheats. It's so hot here in Vegas too which makes it really hard to work on the car even inside my shaded garage but I'm determined to change this myself and save the $550 in labor that a local mercedes shop quoted me. The dealer probably charges much more.
 

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I have a 2015 C300 I purchased used with 81,000kms in August of 2022. Everything was running fine, but now the engine seems to be overheating at about 120kms/hr or more only when I drive around town a lot. It's been happening for 3 weeks. It is intermittent. 150 days til A service according to the car. Wondering if it's the water pump as there are no leaks or anything no engine light etc.

Any help or suggestions would be welcome. I am new to Mercedes and don't know too much about this.
 
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