JohnnyC300

can you please point me to what tensioner, pulleys, and belt you replaced? Hoping to DIY soon and have the thermostat on hand but none of the pieces you mentioned which I'd like to preventstively take care of.

Also, I ordered my thermostat online and it came shipped with 0 padding in an envelop. It got banged around by FedEx for sure, the box inside the envelop was trashed but the pieces seem fine and it's sturdy metal. Should I return and reorder or can I install this one?

Carsy

Don't take that crap from a supplier. Contact them & complain & have them bear the cost of sending it back. Buy elsewhere. Make sure it is a OEM or a reputable German brand.

95Sinned420

The thermostat is sturdy enough that it wouldn't have taken any damage. But the gasket may have been damaged if it was loose in the box.

I bought my part from the dealer. $198. One gallon of coolant and I was out the door around $240.
I highly recommend buying a Wahler brand one for half the price. My MB one says Wahler on it and has the same part numbers. The difference? I paid $99 more to have a Mercedes logo stamped on it. (Actually, I needed a new thermostat right away as I couldn't wait for shipping, that was the premium I paid to pick up locally). No other parts store had Wahler brand and I wanted to stick with OEM/OES.

Adi-Benz

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

$67. C'mon guys.

Atlas Grey

Adi,
Agree. no reason to spend $200 on just the thermostat.
Johnny,
here is what I replaced while I was in there.
Here is a whole kit. Everything you need
https://www.ecstuning.com/b-assemble...FU5YDQodZmALaQ
Belt
Tensioner. You will need a 17MM socket to loosen the belt to take it off along with the proper TorX socket which is used not only on the two bolts on the tensioner but also on the pulleys and the thermostat-keep it handy as it seems Benz uses it alot. I will get you the exact size when I get home
Smooth Pulley (6)
Grooved pulley-(3)This one has to come off anyway to do the thermostat. Go ahead and replace it while you are in there



This diagram shows you how to route the belt. Pulleys 3 and 6 are the ones I replaced. One is grooved and the other is smooth. The one that is in front of the thermostat is the grooved on. You will need coolant to replace what you lose.
You will need a container that is narrow enough to fit between the engine and the radiator to catch as much coolant as you can. Some will still fall to the ground.

So here are you steps to remove the thermostat and replace the belt.
1. Get a container and all your tools ready.
2. Get 17mm socket and long handled ratchet and turn the tensioner until the belt is lose enough to remove.
3. Remove belt
4. Remove upper pulley (grooved one)
5. Remove thermostat catching as much fluid as you can
6. Replace thermostat
7. Replace grooved pulley (3)
8. Replace smooth pulley (6)
9. Replace Tensioner
10. Replace belt following the diagram above while holding the ratchet in place allwoing the belt to slide over the tensioner
11. Remove the metal tube holding the tensioner under tension (you will see it before you install it. It's on the underside of the tensioner.
12. Add coolant to reservoir until its refilled.
13. Trun car on and make sure everything is running right and sounding right.
14. Top off coolant to make sure you have enough. It took about a gallon to fill mine.

That basically covers it. There are quite a few you tube videos out there for reference. All said it should take 2 hours max for a first timer.
Don't buy a cheap tensionr from Ebay for 25 bucks. I did and replaced it twice. Get the gates unit or an OE unit. Trust me. I can now replace a tensioner and belt in 10 minutes.

B737

I didnt read this thread but wanted to post notes regarding this procedure. if im mentioning anything 2nd or 3rd time, all well.

having done this today, i checked a few videos by several people. the best one i found was from FCP Euro, the other videos were a bit of a hack.

few tips...
expect to lose one gallon of coolant (yes i measured). i cut off the top of an old milk container and it helped catch 95% of it. i blew into the upper radiator hose to help force extra coolant out of thermostat. I then used baster method to suck out what i could from thermostat where it kept re-filling. Even after doing all that, you will still spill about a cup of coolant once the thermostat pops free. most of it can be contained if you are ready. I stuffed a lot of "pig mat" below it and it helped buy some time to control the flow. i did not want it getting on the pulleys. where it did, i wiped the pulleys down with alcohol and dried them off with compressed air. stuff a lint free rag to plug engine block, and clean gasket surface.

the plug: do not just pry up on the small gray tab on the plug as the video shows you. use a pick, gently lift on the black U tab on the middle of the plug, THEN slide the gray tab up. squeeze again (secondary lock) and it will release.

route the belt and install the belt on the tensioner last, very easy.

FCP shows them "purging the air" from the system by turning the heat on high and leaving the cover off the coolant reservoir tank while the vehicle is running. this will work initially to replace about a half gallon. after that's done, put the heat on full blast, CLOSE THE LID, and wait about 5-10 min. it will suck down the tank. you can open the lid the pour the other half gallon in. if you feel more comfortable turn the car off.

i left the lid off and was under the car installing the panel covers and the tank overflowed because im a dumbass.

some videos show guys doing this on the M272 without removing the air pump, or idler pulley... removing these takes two minutes and gives you a lot of room, making the job a breeze.

the job takes less than 2 hours working a snail pace while obsessively cleaning. I reset the P0128 code while the engine was running and wrapped up.

also a typo in above post by atlas: upper idler pulley is grooved #6, #3 is smooth. my upper pulley was failed, wish i had ordered at the same time. The smooth lower idler will have to come off to help get straight access to lower bolt on thermostat.

Tensioner bolt= 35Nm
Guide pully= 25Nm
Thermostat= 25Nm

Jess0815

I just replaced my thermostat today, and the check engine light is still on. Does it need to be driven for X amount of miles in order to turn off?

jpflip

Give it a try but I did not have any light after replacement. First start the light was gone....

Jess0815

not want I wanna hear...wonder what could be the issue then 😠

jpflip

You know, Mercedes tried to reinvent the wheel this this "self heating thermostat" and this part seems to be failing often. I would not be surprised if the new one you got is also at fault... I remember checking the continuity of the heating element but that was long time ago. and I think on the one at fault the circuit was open and the new one the circuit was closed... Tried to check both with an ohmmeter if it is possible for you....

Jess0815

Thank you for your help. The light finally went off. Didn't have to drive it for any certain amount of miles. I turned it on and off a few times, and it finally went away. Fingers crossed it stays away...I have to get tags in a few days 🤞

jpflip

Thats great!!! I'm happy for you!

Adi-Benz

Sometimes it takes a while for people, mine was after 1 ride. Thermostat problem is common among all cars, especially BMW, no matter where the car is driven.

atraudes

I'm running into a funny problem after changing my thermostat. I drained coolant from the bottom of the radiator, replaced the thermostat, then filled it back up with some fresh coolant from the dealer (mixed 50/50 with distilled water). I did some driving for 15 minutes or so around the neighborhood, giving it the beans a few times. The problem is the temperature gauge kept fluctuating between 80 and 90 or so. When I'd get moving it'd drop down to 80, then go back up to 90. I left it running in the garage for 10 minutes or so after that to hopefully burp any remaining air out and the temperature held steady at 90.

Normally I'd figure this was a case of the thermostat being stuck open, but I had the heat running the whole time and it was nice and toasty the whole time. Since people are replacing the thermostat due to a lack of heat, I'm wondering if something else is up. At this point I'm going to run it for a few more days to give it a chance to sort itself out but wanted to see if anyone had any thoughts. No CEL yet.

The only other thing worth mentioning is the gray tab you pry up on the thermostat connector snapped off on mine. I managed to pull all of the pieces out and it still seated nicely, it's just not locked into place. I checked again after the drive and it was still secure.

gpdavis2

Great video. Thanks for posting.
Ordered the Mahle (same company made the barrels & pistons kit for my '65 356SC those many years ago) thermostat and Continental serpentine belt for $135, delivered. Will pick up a gallon of MB coolant and provide the video link and parts to my local mechanic. Then........... voila, should have it done for well <$400.

BTW - forgot to mention just how much we like our C350 Sport. Quick, comfortable and reasonably economical (29mpg at 70mph on our trip to Quebec City). And so much more reliable than the '06 Mini (piece-o-s**t) that replaced the '93 E300 (a horrible maintenance hog - wiring harness, trannie parts, radiator, head gasket, engine reseal, etc.- thankfully, much under warranty, but what a hassle) that replaced an '85 300T (great car that simply dissolved (rust) once we passed on to our daughter).

acela11

Hi abrades, had the same thing happening with my 2012 c350. the temp would be at 90 then at 80 and back to 90. brought it to the dealer, i have extended warranty. they said it had no codes so i showed them a video i took of the problem. they changed the thermostat and on the way home from dealer it did the same thing. I'm still researching but i think it may be the fan controller. if u find out lets us know and ill do the same

Nicholi2007

I bought a thermostat Feb 02, 2018 - I believe the mileage was 80k-ish. Fast forward — I now have 146K and it's failing. It has the gurgle sound after shutting off the engine. The fan occasionally comes on with the high turbine speed. I've attempted to bleed it but it does not last for long. Heat eventually stops. Engine temps seems normal. Perhaps a smidge high..

I'm just kind of surprised that I'm having this issue so soon. Shouldn't a thermostat last at least 100k miles?