Another coolant warning question W211 e320 CDI

[MarkOC]

I’ve trawled the internet looking for answers and while I’ve implemented some of the suggestions, I’m still having an issue.
So, coolant, visit workshop warning comes up on the dash. It wasn’t getting particularly hot so I changed the thermostat. Now it gets hot but the fan works intermittently once it reaches temperature. Sometimes it will run for a few seconds before stopping, other times it will run, the speed will vary, but it continues to run until it decides to stop which is when the warning comes up again on the dash. I’ve unplugged the temperature sensor at the thermostat and the fan runs flat out, plug it back in and it stops, which I believe is correct. Also if I turn the aircon off while the fans running, it will stop and the warning comes up. So, the fan works, the temperature sensor on the thermostat is new and appears to be okay. There’s plenty of fluid in the reservoir. I’ve heard there may be another temperature sensor somewhere. The only examples I’ve seen are of a V 6, and they are on the front of the engine. Mine is a straight 6 diesel so I’m not sure if mine has this extra one or not. Any ideas, advice, suggestions or help would b Ed greatly appreciated. Thanks.

 

[onefortheroad]

Did you use a genuine mb thermostat ?

 

[malcolm E53 AMG]

Did you use a genuine mb thermostat ?

Ditto - my first thoughts

 

[MarkOC]

No I didn’t, does that make a difference? I assumed a quality pattern would be okay. I try not to use cheap ones.

 

[malcolm E53 AMG]

No I didn’t, does that make a difference? I assumed a quality pattern would be okay. I try not to use cheap ones.

Not with MB it has comms with the engine ECU

 

[MarkOC]

Okay, I’ll give it a go and see what happens. Thank you.

 

[alexanderfoti]

If its "coolant, visit workshop" it sounds like the fan controller is starting to fail.

 

[supernoodle]

You don't need to pay over the odds for a "genuine MB" thermostat for the priveledge of a pretty box. Covered many times before, MB would source from one of the Tier 1 suppliers like Gates, Mahle, etc.

I put a £25 Mahle thermostat on my S211 several years ago, it's fine.

The only connection to the ECU is the temp sensor which is just a NTC thermistor. The most basic sensor.

 

[MarkOC]

Okay, so I used a Magneti Marelli thermostat housing and sensor. Are you telling me it will make no difference if I use a MB one or a Mahle etc?

 

[onefortheroad]

Okay, so I used a Magneti Marelli thermostat housing and sensor. Are you telling me it will make no difference if I use a MB one or a Mahle etc?

Have a look on your old thermostat and see if the sensor unclips , try swapping it with your Italian thermostat. If the fan still isn't working properly then the issue remains.

 

[MarkOC]

That’s been binned unfortunately. I’ll see how much a MB sensor is I think and go from there. Thank you.

 

[onefortheroad]

That’s been binned unfortunately. I’ll see how much a MB sensor is I think and go from there. Thank you.

One thing I've learned about mercs is they don't care for anything electrical that's aftermarket. Especially abs sensors, yes the thermostat maybe made by other firms ,but not to a mercedes set standard , this is why you pay a premium and don't pay twice.

 

[supernoodle]

Okay, so I used a Magneti Marelli thermostat housing and sensor. Are you telling me it will make no difference if I use a MB one or a Mahle etc?

I am, but obviously not every one agrees. If you want to check the temp reported by the sensor you can see it in a diag tool. Even a cheap OBD2 tool will show you the coolant temp.
Even without that, just measuring the voltage at the sensor will give you a clue. If that's consistent and your fan behaviour isn't, probably not the thermistor.

 

[onefortheroad]

Also check the wiring and especially the connector plug lives, for rot at the fan module . Seems weird how it's all came about since changing the thermostat or is it coincidence??

there is 4 pin connector that goes to the fan and its module
1 thick(red): +12V (always on)
2 thick(black): ground
3 thin (black with red stripe) : +12V (when ignition on)
4 thin (green with blue stripe): signal wire (low voltage PWM signal)

 

[MarkOC]

Okay, thanks for the info. Looks like I’ll be busy at the weekend.
Is there an additional sensor somewhere or is it just the one on the thermostat housing?

 

[ajlsl600]

One thing I've learned about mercs is they don't care for anything electrical that's aftermarket. Especially abs sensors, yes the thermostat maybe made by other firms ,but not to a mercedes set standard , this is why you pay a premium and don't pay twice.

Don't really agree, all to own. There is aftermarket and there's aftermarket. To date over 25 yr and 6 benz I can't recall a febi bilstien issue.
And I only ever had one dud disc which was changed without prob.
Currently I am at benz and febi wheel speed sensors. We see.

 

[onefortheroad]

Febi to me says Chinese. I don't see a connection between an electrical sensor and brake discs

 

[ajlsl600]

Plenty on benz actually made in China brake disc was my only example of having to rtn febi product.

 

[MarkOC]

So I got around to replacing the temperature sensor for a an MB unit. No change. What I have noticed is that it doesn’t matter what the temperature is, if I turn the air con off it flags up straight away. Leave the air con on and it seems to wait until the engine is hot before the warning comes on. I am very confused with this.

 

[alexanderfoti]

It's the fan/controller