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I just replaced the thermostat (borg warner) and waterpump (pierburg/rheinmetall) few days ago. However, it seems the thermostat slow to open on cold start. It waited the temp to reach 102 degree C before thermostat opened. Once it opens, the temp stable at 85 degree or so for the rest of the journey.
First day ok, perhaps there's stil air trapped inside the cooling system, in the afternoon I add about 300mL of coolant in the reservoir to get the level to the max position.
Second day, it happened again, I add another 200mL of coolant to proper level
Third day, happened again (still waiting for 8 hours later in the afternoon before check and add coolant)
I tried to turn on the heater for 5 minutes and it is hot, so the coolant already circulate there (and it does lower the coolant temp further).
In the afternoon drive back home the temp never reach beyond 90 atough the car has been off in the basement of office park for 9 hours.
Is this normal? need several cycles to clear trapped air in the cooling system?
I had to look up what 300ml is. 10oz of coolant, that isnt much when topping off after working on the coolant circuit. I did the same when I worked on my cooling system.
The temp gauge going to 102 doesnt concern me, i've seen mine go to that temp before it lowers back down. My thermostat even says 100 degrees on it.
Are you sure it's at 85, not 90? The temp gauge on my W204 each small line is 5 degrees. My temp hovers at 90 mostly.
BorgWarner should be a repackaged Wahler thermostat, which makes the Genuine Mercedes thermostat.
Keep doing what you are doing. Check and top off the coolant if needed. Inspect everything you worked on to make sure theres no leaks.
I used OBD2 display to display coolant temp (and I also unlocked AMG menu, it does display the same number)
So I should not worry then? After opening it does operate stabile between 85-90C. On old thermostat rarely goes above 90C (it seems lazy/stuck partially open) as engine warms up took a while (10 minutes+), now is much faster. Perhaps the new thermostat needs breaking in or still pockets of air trapped somewhere... (I use 7L of coolant when after replacing the water pump and thermostat)
Its quite normal to add up to 500ml of coolant after thermostat replacement or coolant change, when and if no vacuum assist system is being used.
Up to 3 times adding coolant bit by bit...is normal on my M276.8 within the first under 200KM.
I just replaced the thermostat (borg warner) and waterpump (pierburg/rheinmetall) few days ago. However, it seems the thermostat slow to open on cold start. It waited the temp to reach 102 degree C before thermostat opened. Once it opens, the temp stable at 85 degree or so for the rest of the journey.
First day ok, perhaps there's stil air trapped inside the cooling system, in the afternoon I add about 300mL of coolant in the reservoir to get the level to the max position.
Second day, it happened again, I add another 200mL of coolant to proper level
Third day, happened again (still waiting for 8 hours later in the afternoon before check and add coolant)
I tried to turn on the heater for 5 minutes and it is hot, so the coolant already circulate there (and it does lower the coolant temp further).
In the afternoon drive back home the temp never reach beyond 90 atough the car has been off in the basement of office park for 9 hours.
Is this normal? need several cycles to clear trapped air in the cooling system?
On M276.8, looking at Xentry, 105C coolant temp target is often the 1st hottest temp it likes to achieve.
The target changes over time, but 105C is always part of the target.
.
Later on it will target 90C
And it will target 80C too sometimes
Above is from this test : https://mbworld.org/forums/e-class-w...mperature.html
NOTE : The duty cycle of R48 thermostat heater is opposite value. 0% means full power. 100% means it is OFF. Yes, weird.
If 82% shown it meant 18% duty cycle only is the power to the heater.
M276.xx is already using MAP controlled thermostat, M272 seems to be also already a MAP controlled thermostat.
That blackie small thing is the heater element and NOT coolant temp sensor.
Modern MB engines :
M276.8 ECM is programmed to run coolant hot for efficieny, just like BMWs.
That is why the analog gauge is a liar and will not show 105C.
Only via Xentry or OBD2 gauge, you can see true coolant temp.
I used OBD2 display to display coolant temp (and I also unlocked AMG menu, it does display the same number)
So I should not worry then? After opening it does operate stabile between 85-90C. On old thermostat rarely goes above 90C (it seems lazy/stuck partially open) as engine warms up took a while (10 minutes+), now is much faster. Perhaps the new thermostat needs breaking in or still pockets of air trapped somewhere... (I use 7L of coolant when after replacing the water pump and thermostat)
Speaking of trusting data... you're running
at 1440Rpm
with 12.5 Volts
with LTFT: 9.3%
with 102°C engine coolant temp
12.5V is likely a 12.6V with some chassis drop.
Nothing is unusual....
Last edited by CaliBenzDriver; Yesterday at 02:04 AM.
ok, now that you guys mentioned it, now I am sure that the ECU commanded it to have 99-102 C temp. Because those temp I saw always happen when steady cruising in the highway The temp decreases to 85-90 is few minutes after exiting the highway, then the traffic goes bad. Perhaps is for maximum efficiency on the highway.
My old thermostat probably stuck partially open and that's why I never saw temp above 90C )
Yea, that screen on the dash appearing to show 12.5v while it looks like the car is driving down the road seems off. Voltage should be more like 13.5v or above.
Temp gauge in the instrument cluster is hard to see though looks around 90 c.
As noted above the coolant temp sensor is located on the back of the left cylinder head. The electrical plug on the thermostat is the heating element used to control when the thermostat opens/closes.
The thermostat operates in 4 positions, not just simply Opened-Closed.
During normal operation the temp gauge on the dash will show a corrected, stable temperature. It will not show the actual coolant temperature read from the coolant temp sensor (B11/4). According to the manual for the M272 engine if the coolant temperature is 80 C- 115 C then the temperature gauge will show 90 C. But then you ask why am I seeing the temp gauge climb up to 100 C before it falls back down to 90 C, my guess is that there is some lag from when the instrument cluster makes the correction. I havent been able to find another explanation.
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The temp decreases to 85-90 is few minutes after exiting the highway, then the traffic goes bad. Perhaps is for maximum efficiency on the highway. 
