2007 Mercedes S550
 

Hello all,

First wishing everyone happy holidays. Now onto my issue. I have s550 with 190k miles and have been very good with maintaining the car. I only use brand new Mercedes Benz parts when replacing a faulty part. Needless to say I noticed that I was losing coolant and really couldn’t find out where is was leaking out of. So there is a company that makes dye that you can put in the coolant system to locate leaks. Once you put the dye in and run the system the dye travels through the cooling system you use an ultraviolet flash to try and locate the leak. All components except the radiator of the cooling system has been replaced over the last year or so. I think I located the leak coming from the thermostat housing which would make sense cause even if the coolant reservoir is full and I try to turn on the heat inside the car it just blows cold air. So I am guessing that the thermostat doesn’t actually open allowing the coolant to flow… would I be correct in this assumption? That the faulty thermostat is not allowing the car to produce heat in the car’s cabin?

Couple of thoughts...is the thermostat installed correctly ( correct orientation ) Has the coolant system been flushed properly with the heater on at hot setting to get air out of system? IIRC there is a valve inline that opens and closes to allow hot coolant into the heater. I think there are threads here that indicate replacing it solved the no heat issue.

However if you have bad thermostat housing that leaks, you will need to replace it to solve the ongoing leak. Other wise you will be chasing coolant loss forever. Not to mention a real mess from the leak to wherever it is going to end up.

Thank you for the response. So the water pump was replaced 3 weeks ago cause it was old and I figured that it was the cause of the leak be cause it had a coolant drip coming from it . A mechanic from Mercedes who does work on the side installed the water pump and I am pretty sure it was flushed correctly. Alittle side note the no heat issue started happening and coolant leak happened before replacing the water pump. The no heat issue started slowly. It would work and then slowly faded to cold air.. the valve you are talking about is was also replaced.
https://cimg1.ibsrv.net/gimg/www.mbw...933fdceb5c.png

Yah that is the litle guy.

Does the engine show normal temps when cold and hot ( ie C and middle of the range?)..... low heat issue i would check to see if the valve is closing off during that operation...barring that if it is an electrical solenoid check the plug and harness. Does the car show any codes for this?

That is definitely the heater water control valve located near the firewall and is the typical cause of a no heat complaint. The leak at the thermostat is altogether unrelated and that needs to be sorted also. I am a suspicious person by nature, so I would ask who installed this part for you. Is it installed correctly. Is it an Ebay Chinese pattern part or is it OEM. We have had reports that Ebay Chinese water control valves have had some problems.

yep my sentiments too. Althought we have had posts on here about Genuine OEM parts being DOA ( not necessarily the water control valve)

I will get the valve warrantied and see if that changes anything.

Merry Xmas all!


**** update: So I was able to get the heater control valve replaced today and confirmed that it is indeed not the issue of the no heat problem. I opened my coolant reservoir and noticed that the temperature of the coolant is absolutely ice cold. After looking up on Google different articles of why the coolant temperature would be ice cold even when the car should be been idling for 25 mins or so.. the common theme in the articles was that it’s a faulty thermostat which btw was replaced 11 months ago and is an oem part. So it looks like I will be replacing the thermostat this week which is fine cause that is also where the coolant leak seems to be coming from.

Great news on getting the thermostat sorted. Simply too cold out there to go without heat.

Happy Holidays.

Also I might have found another cause of a leak as one of the spring c clamps is on one of the coolant pipes is missing.. I guess at 190k miles it’s probably expected.

any idea what the stat was - I posted a bit about engine I found on wiki the other day in a different thread - and in it says they didn't have a stat - just some electronic control - I guess either it has a weird beard thing - or it was a w220 idea they binned ?

'A new electronically controlled cooling system has eliminated the need for a mechanical thermostat for improved engine warm-up and optimum control of engine temperature...'

https://en.wikipedia.org/wiki/Mercedes-Benz_M273_engine

well if is electronically controlled , maybe the harness to it is not hooked up?

her indoors with a Ford Focus has an electrically heated thermostat !

the idea is to kill engines - (by making the heater element fail around the 7 to 10 year mark) but lets pretend its just to set the car to run on the hot side of things all the time and thus run more efficiently - then based on the engine ECU's interpretation of how its being driven - it switches on the rapid heat stat to bring full cooling - once the heater fails the stat never opens ever again and the engine goes bang - the only clue that back then (that no one ever knew) you can tell the heater has popped as the cooling fan never stops running

Alittle more update.. the upper coolant hose is ice cold while car is at normal operating temperature.. more and more leaning towards it being thermostat. The coolant I am talking about is coming directly from the thermostat.
https://cimg9.ibsrv.net/gimg/www.mbw...2870779d8.jpeg
The black circle is the upper coolant hose I am talking about.

if it has any electrical connection, it likely will show fault codes ?

(AKA like that ford) is it a heated unit, where the circuit is controlled by the engine ECU - the idea under hard acceleration / driving up hill etc. it heats the stat, opening rapidly, cools the engine then as you back off it closes again

I get one fault code iCarSoft are ‘heating capacity is too low’ 90A2 but when I check on the forums they say it’s the part below which I changed now 3 times so doubt it’s that part .

I also saw this post but I am not sure the wires are the same wires in my car that are in a 2010 since the engine starter battery is in 07 and not 2010.
https://cimg1.ibsrv.net/gimg/www.mbw...50cccd164f.png
Replaced 3 times

see this: https://repairpal.com/mercedes-benz/...er-not-working

it is possible the harness going to valve is faulty or corroded. Most of the site I explored come up with the coolant flow valve you show a pic of. Not sure if it can be installed backwards causing your issue , might look into that. Maybe BOTUS can help with that ??

The fact the upper coolant hose is cold leads to a thermostat issue. I suspect it has been installed upside down or was faulty. Despite you saying a MB tech did this. It is also possible the wrong part was used. Double check with the local MB dealer or order the correct one from FCPEuro. BTW talk to the folks at FCPEuro, not only are the parts all guaranteed but they can ensure from the VIN it is the right part for your vehicle.

thanks for the response and information. So I did alittle research and found that there is fuse associated with the heater. I am also going to check the wiring harness to the valve and also just replace the thermostat myself as it doesn’t system that difficult to do.

That fuse may be for the blower but well worth checking..you never know with MB.
Sucks that you are having to deal with this

Added side note.. my command isn’t plugged in as I am getting it repaired.. don’t think that makes a difference but figured I would put it out there. Also I took the car for a spin and all the coolant hoses are hot including the ones coming off change over valve.

https://www.rockauto.com/en/moreinfo...t=2200&jsn=456

Looks like a standard heated thermostat. I admit 2007 is a pretty early application of it but this type of control was very common in the 2010s.

So I am guessing that my heater exchange is clogged… anyone ever try to flush out the coolant system? Specifically the heater exchange? I see the one pipe coming from the fire wall but not the other one. I am thinking of doing a flush

in this case then , OP needs to repair all leaks /housing issues and replace blown fuse to see if that fixes. Hopefully so !!!!

NVM you posted while i was posting. Sorry i cant help on how to flush the heat exchanger in the cabin. Kevm14 or BOTUS might be able to help though

No blown fuses…