Well the guesses are pretty much what everyone that has looked at thinks plus the possibility of crystals from hard water mix or mixing two different antifreeze together ?? It should have had blue antifreeze in it but it had the yellow/green stuff in it.
It looks like silicone gasket material but feels like gritty stuff?? Also I read that using hard tap water to mix in can cause crystals

 

Zerex G05 is the generally recognized replacement for the MB antifreeze, which is supposedly G05 in a MB bottle. According to the label it is approved for MB 1997-2016.


For whatever reason, G05 is no longer in Amazon's list for these vehicles. The coolants that are in the list are also HOAT, any of which should be cross-compatible. Maybe Zerex is phasing out G05, replacing with G40 / G48. The color is not an absolute indicator; G05 is gold while G48, blue, is also HOAT.

I don't know; coolant types make my head hurt, and unfortunately it is not as simple as going by color.

The only sludging I have heard of is when Dex is mixed with "green" coolant types. Maybe a previous owner topped up with Dex and then green.

Still, if the radiator were plugged, the vehicle would be genuinely overheating, not causing mysterious incompatible readings affected by whether the AC is on.

 

Once again totally agree with you but trying to figure out what the heck is this orange stuff.. in the thermostat it totally coated the small ball in the triangle hole and is also under the stats rubber seal. What ever this junk is it likes to stick to rubber.. when I flushed it 3 times basically running distilled thru it and once using a german brand radiator cleaner… i never saw anything but clean fluid come out which once again puzzled the **** out of me when I took off the stat and hose.
I will let you know what size O-ring fits the hose for future reference… order a few sizes to see what fits the best… I took the brand new one off and measure it to get better reference. Looks like 3.5mm x 40mm or possibly 3.5mm x 39.7 so I ordered both. Something tells me that I might be tearing this thing down again????

 

On this 2011 GL550 the thermostat is a 2 wire and the temp sensor (circled in red with heat shield removed)is tucked very nicely just above the crankshaft sensor .. the crankshaft sensor wires have to be removed to get the torx socket on the small 6 of the hold down clamp. Of course the heat shield has to be removed to see any of this !!! Temp sensor is on back order also…

 

Never mind what I said. My thermostat, at least the spare one in my parts bin, has a two wire connection. This agrees with the wiring diagram. I'm a little puzzled about where I got the idea it is 4 wire.

 

Mercedes in general will puzzle most people even the ones that work on them everyday. My buddy that I showed the parts to today has worked on thousands of MB’s over the years and when he says “no idea” and then “ you only bring me the puzzling ****” ? well just put the dang thing back together and let’s see what happens. I guess I am gun shy from the 500 mile transport GL fuel pump issue!!!

 

I am still waiting on my parts .. there was a screwup on the temp sensor order. I decided to call around and see what was in stock at the local MB DEALERS. First dealer had nothing in stock but the second dealer had 8 in stock…couldn’t get much info out of the parts guy but that sure sounds like they could be having some issues with the temp sensors ? I know it is a real bear to get the part out.. first the crankshaft sensor electrical connector must come off to make room to get the 27 torx bolt out. It is definitely a strange fit also..the temp sensor can spin quite easily and still seal water out?? I replaced the crank sensor since I was there also. Too cheap a part not to .

 

It might have straight threads and a gasket, like a spark plug. Maybe an o-ring that slides into a smooth portion ahead of the threads. Tapered threads are nonexistent in automotive. At least I cannot recall ever seeing them.

Replacing a part such as the crankshaft position sensor is dicey. Yes, a new part should be better, but out-of-box failure on parts is so prevalent these days ... not meaning to complicate your situation; just thinking out loud.

 

No threads just an oring and held in by a small 1 bolt bracket . You can take the electrical connector while it is bolted in and turn the whole sensor very easily ??

 

Eh, as long as the hole and o-ring are clean, they seal well. You might want to smear some silicone grease on the new ring before installation.

Hope this works out for you.

That looks like a mechanical temperature sensor. It's filled with fluid that expands with temperature. I'm surprised MB didn't go solid state by 2011.

 

The sensor is listed for over 600 cars from 2005 until present ? probably why one of my local dealers has 8 on hand ??

 

I am pretty sure from a few minutes of searching it is a
Piezoelectric type of coolant temp sensor.

 

The fluid expands with heat and pushes on the piezoelectric sensor, like a scale. Probably best described as electromechanical. There are entirely solid state devices such as the temperature probe you were using.

 

Not sure it is fixed but it is back together. Under test with the Star System “ Heat Management “ page running … Some things that are pretty much amazing is just how much the ECM works at keeping the motor around 200 F. While idling after a 30 minute drive .. the car will show 200-205 with the heater shutoff but as soon as I turn the heater on it drops to 180. It is around 50 F outside today. On the test drive the temp started out around 180 and as the electronic thermostat did its thing it came right up to 200-205… the picture showing 107c ..224F was the hottest it hit but didn’t stay there too long.
I am still amazed or lost on why and how it can rise so quickly? If the thermostat really closes quickly and just the block coolant rises .. temp sensor adjust quickly and opens the stat??? the good news is the fan stayed very calm mostly ran at 6% even when it hit a peak the fan was slow. Hopefully the AC does NOT over heat the system… I will make a separate writeup for replacing the sensor and crankshaft sensor ..any thoughts welcome .. Bill

 

I posted a while back a sample thermostat map. Mostly I think it is based on engine load. If you monitor the temperature while driving it can be unnerving if you're expecting a stable temperature, as the dash idiot-gauge leads you to expect. The rough rule of thumb seems to be that small throttle openings lead to higher temperatures. I guess the idea is that when you're cruising with part throttle you want better fuel economy, and when you want power, you want a cooler engine, maybe for a temperature reserve, maybe because the engine simply makes more power with lower temperatures.

I've noticed that on trips in warmer weather the fuel economy is better than with colder weather. I assumed this was because the air is denser, but maybe it's due to the thermostat lowering the temperature when using the heater. Is MB afraid we're going to get burns from the heater vent? I have noticed that when it's cold out the heater can actually be inadequate.

I also noticed significant temperature excursions when warming after a coolant change. It is generally more stable during ordinary driving.

Very curious whether your problem is fixed.

 

As soon as the Ohio weather warms up I will know more about if the car with the Overtemps are fixed??
You are absolutely correct that idiot dash gauge does react whatsoever like the Star system which is good because that would be literally jumping up/down. The voltage being sent to the stat also ranges quickly from .4v to 1.0v and the temp reacts super quickly .. not what I expected. If this does fix it I am going to say with 60-70% surety/educational guessing it was the Stat. My reasoning would be I just did not see anywhere near what I saw today in voltage changes and temp changed with it .
Also the drop in temp and it stays there with the engine idling running the heater fan … that reallly stumped me .

 

Weren't you seeing the temperature problems just a couple of weeks ago? Was it warmer then?

It is a tricky situation because you are matching the temperature at the thermostat versus that at the sensor, on the opposite end of the engine.

If the water pump impeller has rusted away, that might cause your symptoms. The coolant simply isn't being moved forcefully, so excess temperature is seen at the back of the motor.

 

Today was getting worried about the exact issue “ water pump” . I kinda of wished I would have removed it? As I was running errands I used the IcarSoft hookup instead of the Star system. Pretty much the same readings. Going along at 96C then for no reason it might drop to 75 and stay there especially if I am at under 15%?load ( heat management info) . I was driving for 3-4 miles at 75C and all of a sudden within a 2 mile spell it climbs to 96C. It will also drop that quick ?? You can see the stat voltage changing between .5v (open) to 1.1v (semi open) I believe 1.8v at startup is closed ???
I have asked my buddy who I sold the 2008 GL550 ( fuel pump replacement)? to put his Icarsoft on it and see if it goes all over the place.
To your original question … yes it was warmer when the original problem of overheat warming came on and i was running the ac.
I just can’t believe a motor could heat up that fast with such a small load going on . Driving around with the info on the Icarsoft is nothing short of maddening !!!

 

That's pretty much the behavior I see when I launch Torque and monitor the temperature. It is unnerving. 80C to 100C and back, with little rhyme or reason. No wonder they made the gauge fake; people would freak out if they paid any attention.

I'll have to try monitoring the temperature while turning the AC and heat on and off.

The voltage applied to the thermostat is only to make it open at a lower temperature. It adds extra heat to the wax motor element. If you disconnected the plug on the thermostat, the engine temp would be stable at a little over 100C. It starts to open at 100C.

The water pumps on these motors are normally very long lived. The only reason I can think yours would have failed is if the impeller had rusted because someone consistently ran straight water in there.

 

Ok that definitely makes me feel better.. yes very unnerving like wtf do I pull over 😂… it changes so dang fast too!

 

Gauges have had a "buffer" built into them for years. On my '97 BMW - I found it takes 50*F of rise before the needle starts to move above "normal". My '98 Suburban's (diesel) needle moves accurately and consistently.

As noted, though, the reason behind this buffer is simply to avoid the dealerships getting the question of "Hey, something is wrong with my engine - the temp needle keeps moving around".

Umm... yeah, that's EXACTLY what is happening inside the engine - but the buffer is made to appease the masses.

 

First sorry for the long drawn out postings.. I guess this happens when you are retired and really want to know what the heck happened.
OK under the old kitchen stove thermostat test.. we use to do this back in the 70’s looking for the thermostat that opened the soonest for cooling.
Also after I took the thermostat apart it definitely looks like orange RTV gasket sealer ?? Will be testing the system later in the day as it warms up to run the AC.
On the stove at 207 did not open.. at boiling water just above 210 it was trying to open ???

 

Sorry for what... for good information?

Based on what Eric mentioned above about 100*C and your stove test, it looks like that t-stat is good.

 

OK warmer day today around 73-75.. Ran the 550 a few miles than parked it and idled with AC running when the coolant temp hit 97C the fan went from 25% to 35% bringing the temp down to 88-89 very quickly .. for the next 30 minutes the coolant temp sat right around 90 with the fan going between 30%-35..
Shut it off and 30 minutes later drove 20 miles and things are looking good.
I cannot say for 100% certain which fixed the coolant sensor or thermostat but I was not happy with the thermostat stove testing … the stat definitely did not open all the way even at boiling.
Hopefully onto other fun stuff like going to some baseball stadiums real soon… Pittsburgh, NY and St. louis this summer!!!!
Still would love to know what the heck this orange stuff is??

 

I'm not sure what the stat is rated for - in terms of what temp it should be "fully open" at. It would probably help to know that.

Did you happen to do the stove test to the new stat to see how it functions?