OM651 - Coolant Temperature Sensor Problems

[paul73mt]

In my own experience I find that the first thing people do when the car takes longer than usual to get up to temp is blame the thermostat. So they change it and hey fault fixed. But what they actually done was replace the thermostat THEN put in fresh clean new coolant fluid to the exact mixture that it is supposed to be. So majority of time it isnt the actual thermostat. People tend to top up with coolant and keep doing it. The mixture ends up that lean that its almost 100% coolant. The chances of that getting up to any kinda of temp close to your 80/90 are quite slim. What I do when I get a car in with similar complaint is flush the coolant system a few times and simply mix the proper coolant concentration according to the car and the problem is solved 99% of the time. The ones I have had to change thermostats on are ones that are stuck closed and cause more serious problems. I suggest flushing system and replacing ur coolant 1st properly before moving onto the thermostat.

What about when a car has been into MB and they have tested the coolant to see its ratio, They have tested the cooling of the car and found to be ok, but this was done when it had already been at its normal operating temperature. Does anybody know if you can force the thermostat open with star via the ecu ???

 

[paul73mt]

Since last Monday morning, my Merc is displaying the exact same symptoms as described above... from a cold start, external temp@ 12c, staying at low 60's for 10-12 miles before climbing up to the 90 mark, but staying at that temp from that point onwards ( unless stopped for awhile and allowed to cool down ) Same thing happened last night, stayed at the 60 mark, despite climbing a serious hill, before hitting the 90's. So Thermostat I guess. Does anyone have the correct part Nr for the 2010 E Class W212 2.1 diesel, with OM651 engine? Watched a video on You Tube last night, showed a Thermostat being replaced on a OM651 Engine...does not look that complicated, but would be nice to talk to some one here on the forum who has actually done a replacement. There is always something you will meet when doing the job yourself, that was NOT shown on You Tube .. LOL As another possibility, could be faulty sensor?

Mine would always go up to or just over the 80 degree mark then go up n down but not normally any lower than 70.

My thermostat is this one: Genuine Mercedes-Benz OM651 Engine Cooling Thermostat A6512001500 NEW | eBay

If you email then with your chassis number Michael will confirm, They also do the coolant 5L was £36 (red in colour) so if your gonna do a 50/50 mix that should cover you quite well.

 

[Justintyme]

Mine would always go up to or just over the 80 degree mark then go up n down but not normally any lower than 70.

My thermostat is this one: Genuine Mercedes-Benz OM651 Engine Cooling Thermostat A6512001500 NEW | eBay

If you email then with your chassis number Michael will confirm, They also do the coolant 5L was £36 (red in colour) so if your gonna do a 50/50 mix that should cover you quite well.

Thanks Paul, that's the Thermostat I will go for. I had already bought 5 ltrs of Comma Xtream anti freeze concentrate. I was in any case going to do a complete flush and change...there is a small leak occurring, 1.5 lites since January this year, covering 7'800 Klms. Afraid of adding more antifreeze, while not knowing which kind of coolant was already in it ( and knowing the dangers of mixing fluids !!! ) I only topped it up with ordinary water. So now the flush, change and thermostat will all be carried out at the same time. Hitec has posted a very interesting article ( see above ) about the antifreeze becoming too "Undiluted" and this could give the same symptoms as listed above. We will see. If I open the drain screw on the bottom of the radiator, will ALL of the coolant drain out through this? Or are there more drain points in the system?
Thanks again for your help, Paul.

 

[HITECH]

The more u top it up with water. the more likely it is to boil away the thinner it gets. Then the level gradually goes down. This is why it is very important to mix to the ratio that is recommended. The so called tests by the dealers to test the ratio of the anti freeze are a complete and utter con. they pop the cap off the expansion tank and if its to level they pop it back on and tick the box. Im offering some advice on this from recent experience with a engine core plug corroded and leaked ( or freeze plug as they are better known ) i would top up with coolant. temp would take longer to get up. the leak it got worse i decided to stop topping up with coolant as it was leaking out anyway. started topping up with water. it started getting thinner in which case the temp started getting up quicker but it would boil away. All the 3 weeks i lived with this before changing the core plug i observed the diffirent effects this had on the engine temp purely to watch closesly that i didnt fry my engine. Just like to add the coolant system got well flushed out good n proper before a clean mix of coolant went into it after the core plug was replaced. It takes about 5-7 miles to get up to temp and thats actually perfectly normal. Then it sticks right on the 80 steady unless im in a rush and then it sits just above the 80

Good Post, Hitech. Because the fluid is going to be replaced anyway, do the change and flush first, drive and see what are the results. In my case though, since I got it last January, twice the low level warning came on, and each time I topped it up with 500 ml water, so I presume that the mix has been thinning rather than becoming more antifreeze pure. I had already bought 5 ltrs of Comma Xtream 48 concentrated, as a coolant change was planned, ever before the temp started to act up. So now I will drain, flush and refill. On the U tube video I watched, the drain is shown as being on the bottom of the radiator, (Red Cap) with outlet beside it to take a plastic pipe. Will ALL the water drain out via this pipe? Or is there other outlets as well? Far as I know, the total capacity is 10 ltrs, so if I measure what drains out, and it comes to 10 ltrs, it will be a complete drain?

 

[Justintyme]

The more u top it up with water. the more likely it is to boil away the thinner it gets. Then the level gradually goes down. This is why it is very important to mix to the ratio that is recommended. The so called tests by the dealers to test the ratio of the anti freeze are a complete and utter con. they pop the cap off the expansion tank and if its to level they pop it back on and tick the box. Im offering some advice on this from recent experience with a engine core plug corroded and leaked ( or freeze plug as they are better known ) i would top up with coolant. temp would take longer to get up. the leak it got worse i decided to stop topping up with coolant as it was leaking out anyway. started topping up with water. it started getting thinner in which case the temp started getting up quicker but it would boil away. All the 3 weeks i lived with this before changing the core plug i observed the diffirent effects this had on the engine temp purely to watch closesly that i didnt fry my engine. Just like to add the coolant system got well flushed out good n proper before a clean mix of coolant went into it after the core plug was replaced. It takes about 5-7 miles to get up to temp and thats actually perfectly normal. Then it sticks right on the 80 steady unless im in a rush and then it sits just above the 80

I agree completely Hitec, and the only reason that I used plain water was I could not find out what type of antifreeze was already in it....and there are some horror stories on the forums about mixing different types of antifreeze, so a complete flush and change is the plan. During the flushing process I will add some leak finder fluid, and see if I can pinpoint the actual leak. Nothing very visible that I can see, save a very faint watermark underneath what I presume is the water pump. Was it a difficult job replacing the core/freeze plug? Did you do it yourself? When I am refilling it, I will test the specific gravity of the mix,,,,,and that will be a good reference for topping up in future.

 

[HITECH]

No I didnt do the freeze plug myself. That was a NIGHTMARE to get the whole thing out as one on mine was actually a threaded plug which had molded itself into the internal thread. Had to remove the DPF and the CAT to just get to it. It had to be heated up by another mechanic and then what was left was the outer lip molded onto the internal thread. that required more heat and physically ripping it out. Its a tricky thing to do because its important not to overheat the block or wreck the internal thread for the new one to screw into. An important tip before removing the left over bits of the cap stuck in the internal thread is ENSURE THAT ALL OF THE WATER IN THE COOLANT SYSTEM IS ALL GONE because if its not then u wont get any heat onto the bits that are left to heat them up and rip them out. Your car sounds like its newer and lower mileage so its highly un-likely but like mine if its been mis treated by a previous owner and there has been no coolant in the system at one time or other then its a strong possibility could be a freeze plug. If u give me your email i will send u some pictures of this nightmare job and the access hassle. I dont think anybody else in this forum has actually changed a threaded freeze plug. Only a press-fit one which are easily removed with less hassle. One good thing was I manually cleaned out my DPF which was giving me no problems anyway. The soot content before was something like 15% and the ash content was 3 grams. After i cleaned it out and re-fitted it, both were at Empty 0%. Well the ash content was 0 and the soot content was reading -3gms. So it was actually a lot lighter after being cleaned out than it was originally when it was brand new. I strongly recommend cleaning out ur DPF if u ever take it off ( if u have one ). The trick with it is ENSURE THAT IT IS DRIED OUT FOR LONG ENOUGH WITH COMPRESSED AIR. And u give it a good hammer or bang as ur jetwashing it out after a soak in turps/acetone because if u dont give it a good hard hit with hammer or bang it off the bench/ground you wont actually dis-lodge the ash/soot properly. I was quite impressed with the result after doing it. some turbos on the mercedes cars have just 1 red turbo seal that the air intake fits over like the w03's and some of the newer ones. The gravity tests for the coolant are extremely unreliable. I personally prefer to put n the coolant myself on any job then i know that whatever happens to the customers car, that part of the system is 100% when its picked up.

I agree completely Hitec, and the only reason that I used plain water was I could not find out what type of antifreeze was already in it....and there are some horror stories on the forums about mixing different types of antifreeze, so a complete flush and change is the plan. During the flushing process I will add some leak finder fluid, and see if I can pinpoint the actual leak. Nothing very visible that I can see, save a very faint watermark underneath what I presume is the water pump. Was it a difficult job replacing the core/freeze plug? Did you do it yourself? When I am refilling it, I will test the specific gravity of the mix,,,,,and that will be a good reference for topping up in future.

 

[pembssurf]

+1 for stat. Same engine here and on my second stat in 3 years with the same symptoms. Weakest part of the whole engine. That being said it’s a cheap easy fix.

 

[paul73mt]

The more u top it up with water. the more likely it is to boil away the thinner it gets. Then the level gradually goes down. This is why it is very important to mix to the ratio that is recommended. The so called tests by the dealers to test the ratio of the anti freeze are a complete and utter con. they pop the cap off the expansion tank and if its to level they pop it back on and tick the box. Im offering some advice on this from recent experience with a engine core plug corroded and leaked ( or freeze plug as they are better known ) i would top up with coolant. temp would take longer to get up. the leak it got worse i decided to stop topping up with coolant as it was leaking out anyway. started topping up with water. it started getting thinner in which case the temp started getting up quicker but it would boil away. All the 3 weeks i lived with this before changing the core plug i observed the diffirent effects this had on the engine temp purely to watch closesly that i didnt fry my engine. Just like to add the coolant system got well flushed out good n proper before a clean mix of coolant went into it after the core plug was replaced. It takes about 5-7 miles to get up to temp and thats actually perfectly normal. Then it sticks right on the 80 steady unless im in a rush and then it sits just above the 80

I see yours is a C220 perhaps the 250 and 220 have different 'normal' temps as mine sits at around the 90 mark (when it gets there ) my old C350 CDI also sat at the 90 mark

 

[Justintyme]

Time to change the antifreeze has finally arrived, so this morning I took the plunge.I ran the engine until it reached above the 80c, with the heating set at max, then drained it. I measured what came out, and it was a little over 6 ltrs. I was under the impression, that the capacity of the w212 2.1 diesel was 10 Ltrs, but all I could get was 6?? Anyway after draining it, I let it cool down a bit more, as I don't particularly like putting cold water into a hot engine..and then filled it up with clean water, same procedure, run the engine up to 80c, heating on max, and drain it again...same result 6 ltrs. So let it cool down a bit ( again ) and filled it with Comma Xtream G48 mixed 50/50 with distilled water, I kept topping it up as much as it would take, and then drove it, heating still full on. Temp rose to 90c, but after a while heating temp dropped, airlock, I guess? Anyway drove it home, let it tick over for a while before switching off. Allowed it to cool down, then topped the reservoir up. I guess that there is still some more air in the system, as it will still need 1/2 to 3/4 ltr to make up the 6 that was originally drained from it.
Now I just have a question concerning compatibility. The antifreeze I used Xtream G48 meets MB Approved 325.0 , and it is suitable for Merc's up to 2013. It's blue in colour. I also have a brand new litre of Mercedes Anti Freeze, A 000 989 08 25 10, also MB 325 spec. Are these two compatible with each other? any information would be appreciated. Or any comments about the process I used?
As suggested by Hitec, in a lot of cases, it's not the thermostat which is gone, but just the fluid, which has become too diluted, I will run it now for a few days, and check if it cures the temp issue it was displaying.
Best Regards, Justin

 

[Mr Filipov]

@Dickie Fix when I was with Mercedes I used to use a garage called Star Auto Services. They are based in Huntingdon, which is not too far away form you. While the garage does not look like anything special the guy there is very knowledgeable and the charges are very reasonable. In case you have not done the job it might be worth giving him a ring. Ask for Stuart.

 

[Dickie Fix]

@Dickie Fix when I was with Mercedes I used to use a garage called Star Auto Services. They are based in Huntingdon, which is not too far away form you. While the garage does not look like anything special the guy there is very knowledgeable and the charges are very reasonable. In case you have not done the job it might be worth giving him a ring. Ask for Stuart.

Many thanks for that. No, I've not changed it yet as it's been working perfectly since I gave it a damn good talking to and is getting up to 90 degrees within 5 miles. However, I have a new thermostat so am ready to go should it act up again and will give Stuart a call.

I know some have questioned the condition of the coolant, but this is a 3 year old car which has never needed the coolant topping up. Also, the coolant has a 10 year life, so it should be another 7 years before it needs changing.

 

[Mikegrieve]

Hi. Newbie to this forum
My 2015 e220 BlueTEC had the same problem with low temperature indication(and no green eco light) I got my local independant to swap the start assembly and what appears to be two sensors. All perfect for the first drive to home. Alas the very next day all the same problems returned. Due to lock down I've not bothered with this except when MB Loughborough serviced it last week I asked them to check if there's a fault and they said oh goody! £110 to put it on star to check it. This despite it being the big service at 55000 miles & £655.00. No help there, I won't play their games. Oh & 2 complimentary nox sensors fitted..
So my new sensors & star did nowt to help.
Any ideas please.
Mike

 

[Mikegrieve]

Sorry new stat and its sensors

 

[Tonygw]

MikeGrieve, Dont go to MB loughborough, go to MB automotive, just round the corner past B&Q. They will be half the price and will not charge for simply taking a look,. They are all ex MB mechanics and very very knowlegable... Been a few times and always come away feeling like they have done a good job. Very friendly to. I don't work for them and don't know them just had really good service there, so happy to recommend..
Oh and they have full access to the MB electronic service records, and star diagnostic information and only fit genuine MB parts (which they get from MB loughborough LOL)

only problem is they are VERY busy!

 

[Mikegrieve]

Thanks for that tip Tony. Sounds like a result to me.