W212 2009 CDI Engine Temperature
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Joined: Nov 2012
Posts: 39
Likes: 2
From: croatia
W211 06"
W212 2009 CDI Engine Temperature
Hi, im lately having issues when driving vehicle in morning (any time of day - cold start is what it needs), as I am driving normally engine temperature is rising normally but when it reaches 80oC (not 85-90oC standard working engine temp.) the engine temperature goes a down bit to around 60-65oC then it needs some time to back again and to reach 85-90oC, not sure what is going on, i went to 3 very experienced workshops mechanics and they are not sure what is the issue, but all of them say its thermostat, but i already replaced 3 brand new original mercedes thermostats and this issue is still going on.
Heating in vehicle is working okay, anyone have idea what could be wrong?
W212 2009 E250CDI OM 651 924
Heating in vehicle is working okay, anyone have idea what could be wrong?
W212 2009 E250CDI OM 651 924
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Joined: Jan 2009
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From: V E G A S
1922 Ford Model T / no OBD
Do you have classic thermostat, or electrovalve controlled by computer?
Could be your temp sensor is acting. Did you verify it with scanner?
Could be your temp sensor is acting. Did you verify it with scanner?
Last edited by kajtek1; Apr 25, 2019 at 11:53 PM.
Thread Starter
Junior Member
Joined: Nov 2012
Posts: 39
Likes: 2
From: croatia
W211 06"
Dont have rooms in split :P
Thermostat Housing Genuine OEM A 651 200 28 00If you look at part i think it have 2 sensor only, no electrovalve (not sure)...How do you mean verify with scanner, you mean diagnostics?Il upload video tomorrow on how issue looks like
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Joined: Jan 2009
Posts: 9,224
Likes: 1,798
From: V E G A S
1922 Ford Model T / no OBD
I check the part number and it sure come as a nice piece of puzzle.
Pelican parts confirms that as traditional thermostat.
Why I ask, before paraffin-driven thermostats don't misadjust. When they fail, they either stay open or close, so when you have complain about 10-20C difference, that most likely is something else.
Hook up scanner and compare scanner reading to dashboard reading.
MBWorld Fanatic!
Joined: Jan 2009
Posts: 9,224
Likes: 1,798
From: V E G A S
1922 Ford Model T / no OBD
Man, you need to cure those shaking hands 
Your thermostat does act funny. It is normal that when opening, slight delay can make temp going slightly higher and then drop couple degrees, but your drop 20C,
We have the same engines, but for different markets they have different programming. Still my OM651 takes like 5 miles =8km to get to 80C starting in warmer temperatures than 20C outside.
Than my thermostats stay firmly at 85C (have 2 of the same models).
Your symptoms would indicate air bubble in the system, so that is what I would check to start.
Than dashboard gauge is dummy gauge, so for real troubleshooting I would use a scanner.
Your thermostat does act funny. It is normal that when opening, slight delay can make temp going slightly higher and then drop couple degrees, but your drop 20C,
We have the same engines, but for different markets they have different programming. Still my OM651 takes like 5 miles =8km to get to 80C starting in warmer temperatures than 20C outside.
Than my thermostats stay firmly at 85C (have 2 of the same models).
Your symptoms would indicate air bubble in the system, so that is what I would check to start.
Than dashboard gauge is dummy gauge, so for real troubleshooting I would use a scanner.
Thread Starter
Junior Member
Joined: Nov 2012
Posts: 39
Likes: 2
From: croatia
W211 06"
Man, you need to cure those shaking hands
Your thermostat does act funny. It is normal that when opening, slight delay can make temp going slightly higher and then drop couple degrees, but your drop 20C,
We have the same engines, but for different markets they have different programming. Still my OM651 takes like 5 miles =8km to get to 80C starting in warmer temperatures than 20C outside.
Than my thermostats stay firmly at 85C (have 2 of the same models).
Your symptoms would indicate air bubble in the system, so that is what I would check to start.
Than dashboard gauge is dummy gauge, so for real troubleshooting I would use a scanner.
Your thermostat does act funny. It is normal that when opening, slight delay can make temp going slightly higher and then drop couple degrees, but your drop 20C,
We have the same engines, but for different markets they have different programming. Still my OM651 takes like 5 miles =8km to get to 80C starting in warmer temperatures than 20C outside.
Than my thermostats stay firmly at 85C (have 2 of the same models).
Your symptoms would indicate air bubble in the system, so that is what I would check to start.
Than dashboard gauge is dummy gauge, so for real troubleshooting I would use a scanner.
I also noticed when watching constantly rising temperature in given time and speed of vehicle and its also warm outside (spring time) engine temperature is going same speed upwards then when drops from 80oC to below then sometimes it takes almost 10-15 minutes to go to 90oC.
Its like around 80oC is some kind of barier for engine temp.
Yes i will update how things progress...
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Thread Starter
Junior Member
Joined: Nov 2012
Posts: 39
Likes: 2
From: croatia
W211 06"
UPDATE:
car mechanic tested vehicle when it was cold start and when temperature started to drop on dashboard the diagnostics was showing the engine temperature didn't go down...
He couldn't do more and suggested me to go for vehicle electrician.
Vehicle is now at electrics specialist and gonna see what happens.
car mechanic tested vehicle when it was cold start and when temperature started to drop on dashboard the diagnostics was showing the engine temperature didn't go down...
He couldn't do more and suggested me to go for vehicle electrician.
Vehicle is now at electrics specialist and gonna see what happens.
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