Marko2011

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

Plutoe

Very strange however I would make sure your thermostat and sensor is functioning properly
PS: do you have any rooms in split?

kajtek1

Do you have classic thermostat, or electrovalve controlled by computer?
Could be your temp sensor is acting. Did you verify it with scanner?

Marko2011

Car is at mechanic right now and he will do complete test, we gonna see.
Dont have rooms in split :P

This is the part:
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

kajtek1

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.

Marko2011

[url=

You Tube

]Video of issue - youtube[/url]

kajtek1

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.

Marko2011

I know camera is not stabilized and cant do anything with that, roads are what they are here.
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...

Marko2011

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.