RichieBoy

Had some weird cooling issues with this car in the past replaced the thermostat water pump and expansion tank

In the images attached my temperature gauge is at the highest it gets and the lowest it gets depending on where I’m driving. If it’s highway or through the streets.
is it normal for the gauge to fluctuate that little bit? Or is it supposed to be locked and not move?

This is the lowest

Highest is right on that line that it’s on

CaliBenzDriver

the first thing to know is the temp gauge is software driven. Temp displays adds to the dashboard looks... It's part of what savy buyers like in a German premium car. So don't sweat too much about funny gauge.

This topic has been super well covered by master @S-Prihadi who discovered this idiot gauge with us.


> Things you can do regarding engine TEMPS:

1. Scan your live temperature data
2. Replace engine radiator after 120kMi
3. Burp circuit to help coolant circulation
4. Check the A/C condenser allows air through
5. Keep moving for cooling air circulation
6. Upgeade to Amsoil for best viscosity specs
7. Easy on the redline rush

RichieBoy

have all live data . If I’m on the highway and open it up it drops to like 180f and the highest it gets is 226f
normal driving on the highway sits at 215f never gets above 226f and car has 82000 miles

And usually the car sits at 215-218f

CaliBenzDriver

The deal here is Bosch ECU actively manages the engine temperature to expedite warmups.

The engine features a thermostat remote controlled by the ECU through a thermostat heater. Temperature is dialed according to variable ECU preferences.

The coolant pump impaler is reputed to be undersized to "help save gas" but comes with a secondary/stationary electrical helper pump that can run to help circulation needs.


In a nutshell:
The gauge lies a little because the temperature swings are managed. by software objectives....
What could go wrong, right?

The fancy thermostat can get slow to open...
Check engine ECU for active DTC
Measure thermostat heater coil: not open/infinite

I don't know that this particular system is built for premature failures.
So this may be A-okay as is...
🤞

ChrisHimself

thats exactly what my car runs at, it runs a little cooler at night at 90mph but thats the operating temp. Oil pressure and temp gauges are usually really bad at telling you what the actual temp is like others have said. My coolant hose popped off (REIN water pumps are ***, the clip and casting were off) and it didn't tell me anything useful until the fans were roaring and then the temp only went up like minutes after I shut the car off.

if your car is operating properly it pretty much runs at the temperature the ECU tells it to at all times via thermostat/fan regulation which is all DME/MAP controlled. Mercedes are such control freaks that it mostly has ONE temperature, until something is very wrong. Having the car run cooler is nice but you wouldn't notice it for the most part because the ECU would just cut the fan and close the thermostat to bring it back to the magic number where everything works properly.

RichieBoy

ok so u think I’m fine and I’m just over reacting lol

ChrisHimself

yeah man just make sure it's filled to capacity with the right stuff and/or whatever universal HOAT without silicates at the minimum.

if you have a problem with the thermostat it'll code. It's ECU controlled, hell everything is on the car.

cars are particular about type of coolant since Europe is super strict on environmental stuff, so the coolant pour is designed to last 10 years, 125k miles which is nutty but I've seen it. Once the coolant degrades or you're mixing with substandard coolant, you can notice a dropoff in efficiency and corrosion resistance (it turns brown) but if your stuff is bright and clear nothing to suspect there.

If you're looking for something to do on the car, Continental DWS06+ or Michelin AS4

RichieBoy

ya i replaced the thermostat and bleed it like 1000 times lol and vacuumed the system

BenzV12

I have not paid that much attention to my gauge but mine also fluctuates a bit but not that much .Sometimes, I hear the fans kick in when I get out the car I think the car knows when to activate those fans assuming the engine gets hot and needs to be cooled down

Raj1471

My temp gauge fluctuates a little as well. Every now and then I check the expansion tank to make sure that the MB spec coolant is sufficient and top off if necessary.

Chevota

I watch what computer says the temp is, which I'm sure isn't 100% accurate but it's a zillion times more accurate than the dash gauge. I can watch the ECU temp go from say 185 to 230F but the dash barely moves and never registers above 100C.
I think there is some kind of international automotive agreement to make sure the dash temp gauge is as inaccurate as possible, and maybe even awards given for the most inaccurate. If you want anything resembling accuracy you need to buy an actual mechanical gauge, like AutoMeter or whatever. Even the cheapo mechanical gauges I've tried are pretty much spot on.
Or use an OBD dongle and app to read the temp from the oem sensor. Just a cheapo dongle like on Amazon for $10, plus and app like Torque Pro, or the free version, can get you that. Then you can compare to the dash gauge and est temp. Like 90C =100C, 91C = 225C, 93C = 250C. I know it sucks, but it is what it is. And they do get hot at idle. The fan doesn't come on until the last minute, and only enough to prevent disaster. The spark timing is retarded to make it run hot, on purpose! You can thank the EPA.

Gas gauges are normally similar, but not nearly as bad. Again, the gas level via the ECU is far more accurate and can be read via an app. I've been watching mine and it's pretty frikkin accurate. If it says the tank is 20% then it takes almost exactly 80% when I fill at the pump. The gauge on the dash not so much, but a 100x better than the temp gauge.
The tach is not accurate either, in my car, but I don't have an accurate tach to compare it. I know it's wrong for other reasons, like bouncing off the rev limiter set to 6300 when the tach never hit 6k. I don't believe it's wrong on avg, it just doesn't respond quick enough, so when you floor it you could be >500rpm higher than what it says.
The speed is more or less accurate, but like all car mfgs they add ~1% for butt coverage. So with slightly larger tires in back I'm just about spot on. The speedo is an average of the front and rear, at least mine is, so it took 2% more rear tire to net 1% at the speedo.