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Does the coolant temp reading for the guage the same as what is read through a scanner? I monitored my temp this morning through a scanner for about 30 min and it fluctuated from about 90 to 105. However on the dash the temp pretty much stayed right around 90 C. I have been keeping an eye on it as a couple times the temp on the dash jumped from 90 to about 110 instantly then would instantly go back down. Suspecting a bad temp sensor or air in the system? Also on the last couple of times driving when starting after sitting at least 8 hours the temp was reading about 60C before being started.
Last edited by jschandler; Jun 9, 2021 at 10:42 AM.
My car reads just over 80C all the time, and it has fresh coolant. I am surprised by these MB gauges because every other vehicle I've owned always reads dead center on the temp gauge. Its just MB gauges that seem to read above dead center in various models. I suppose over 80C (90-100) is what is considered normal for MB vehicles. At least that is what I have been reading here on the forum.
Does the coolant temp reading for the guage the same as what is read through a scanner? I monitored my temp this morning through a scanner for about 30 min and it fluctuated from about 90 to 105. However on the dash the temp pretty much stayed right around 90 C. I have been keeping an eye on it as a couple times the temp on the dash jumped from 90 to about 110 instantly then would instantly go back down. Suspecting a bad temp sensor or air in the system? Also on the last couple of times driving when starting after sitting at least 8 hours the temp was reading about 60C before being started.
Hi jschandler,
I’m currently facing the same issues with the coolant readings through my scanner. Wondering if you managed to fix it or is it normal? Thank you.
for my case on my w221, upon cold start, with highway driving for the first 20mins, the coolant temp goes up to 110C the drops to 90C and does this for 3 times before stabilising at 90-95C. On next start up, coolant temp doesn’t do this anymore and will be solid around 90-95C.
Thermostat was replaced new and coolant system bled but this still happens
The gauge and scanner read from different sensors. Your scanner shows the real ECU data.
The gauge is buffered to look steady, so its 90 reading is "normal." But your scanner's 105 reading is the true temp.
The instant jump to 110 on the dash, and the 60C reading on a cold start, point directly to a failing coolant temperature sensor. That's your most likely culprit. Get the sensor replaced.
It rises steadily to 110C and drops to 90C steadily as well. Does this 3 times every morning after a cold start while driving. Just worried something is failing or not working as intended. No faults on cooling system and no overheating warning as well.
stopping at the red light or idling doesn’t spike the coolant temp
1. Is the thermostat genuine or after market and did you replace the housing as well?
2. Does the M272/3 have a separate sensor for ECU and Dash?
Engine COLD, loosen the expansion cap and start the engine. Leave idling. Set the cabin temp (including rear climate if fitted) to HI but set the fan to minimum. Once the thermostat has opened, wait 5 minutes before switching off. Allow to cool, check the level and top up as required. Refit cap.
coolant bled a few times and there shouldn’t be any air bubbles inside anymore.
starting to wonder if it is a normal occurrence to increase the engine temp or heat up the catalytic converter after a cold start. After the 110C to 90C movement 3 times, temp stabilises at 93C
coolant bled a few times and there shouldn’t be any air bubbles inside anymore.
starting to wonder if it is a normal occurrence to increase the engine temp or heat up the catalytic converter after a cold start. After the 110C to 90C movement 3 times, temp stabilises at 93C
I would think the secondary air pump is responsible for quickly heating up the cats on cold start.
Heres some info on the M272/273 thermostat thermal management functions:
The temp gauge in my 2010 W204 with M272 engine is very consistent. Steadily rises to 90 then will stay there.
Since the cold weather is here I notice if i turn the heat on before the engine gets to temp the temp gauge will go down a little then continue to rise. Thats probably the heater valve opening introducing cold coolant from the heater core into the system.
I have seen the temp gauge down around 80 once in awhile which stands out since im used to seeing it at 90. I see this when cruising on the highway around 70mph.
I took some photos to show the temp gauge. had the dash display showing the engine on time. Looks like it takes around 10 minutes for my engine to get to 90 and stay there.
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