UberFusion

On my wife's 2012 ML-350 Blutec the "low coolant level' message light has started coming on.

I've checked the coolant level and it's right up to the proper level. I quickly checked with our repair guy (who recently serviced the vehicle, checked everything and topped up all the fluids) and he thinks he thinks it's probably the sensor...

I looked around on the web and can't find any good data on this sensor, what it looks like and where it's located, how to check it, etc - figuring I'd have a look at it myself (fairly handy with these types of things)...

Can anybody shed a bit of light on this and provide some info / suggestions...

Hopefully it's maybe a bad connection or if defective I could order in a replacement sensor and swap it out myself...

Many thanks and regards - and Happy Holidays.

UberFusion

Had a good look at the coolant expansion tank where I'm pretty sure the sensor is located - and I think the sensor is mounted underneath the tank...
The tank is pretty well bolted in from underneath but I notice there seems to be an access panel (about 6"x 8" in side) right underneath in front driver's side plastic wheel well.

So my question is now - how do I pop open this access panel?
I quickly tried putting a flat screw driver under the panel edge but I didn't want to put too much pressure on it for fear of breaking something...

Hopeful someone can provide some advice for opening the access panel...

UberFusion

Was able to open up the access panel by prying out the plastic fastener and then sliding the panel to disengage it from the opening...
but it doesn't allow much access to the coolant expansion tank.

Have now determined that the coolant tank sits on some rubber mounts underneath and the tank is held in place by a single bolt behind the tank ... so tomorrow I'll remove the bolt and ease out the tank so I can get a better look at the bottom of the tank and hopefully figure out the level sensor...

350MH83

That's a wild guess, but what if the sensor is a resistivity sensor (reads low resistivity when in fluid, and high resisitivity when out of fluid), and the MB technician topped it up with some weird fluid that increases the coolant resistivity? Im saying that because this happens a lot with windscreen washer... They use resistivity sensors, and some after market liquids will trigger a false positive.

UberFusion

Thanks for the comments 350MH83 - interesting theory. I'll follow up with my repair shop to see if this could be an issue...

This morning I undid the nut (on a threaded stud at the back of the tank) that holds in the coolant expansion tank and tried to ease out the tank but it stills seems to be holding tight. The tank is mounted underneath on two rubber mounts which I think are just pressure fitted into the frame below - but I didn't want to use more than gentle pressure in case I broke something. Hope someone can provide some advice on easing out the tank...

While working on trying to remove the tank I did find 2 small wires that go up into some kind of a 'fixture' on the bottom of the tank - which I presume to be the elusive level sensor - but the tank needs to unmounted/removed in order to get better access to the sensor wiring/fixture...
... so I'm back to figuring out how to remove the tank...

Cheers - all the best for the New Year.

theboogers

My 2014 350 bluetec w 8k miles is also showing low when temps are colder. Seems a couple of people are having this problem. I will not be taking it for service for a few months but hope there is a answer.

Kartergreg

I had this issue with my 2013 Bluetec several months ago when the outside temps dropped. I added a little more than half a cup of distilled water to the coolant reservoir and that solved the problem.

Just curious, did you try adding any fluid to the reservoir first?