Erratic temperature gauge

[C220jim]

Hi guys I'm a newbie to the forum so please bear with me,
I'm having issues with my temperature gauge on my 2011 c220 approx 50k miles, on my daily commute to work my temp gauge seems to fluctuate about 9 miles into my journey, the gauge will be sat at around 80deg (which I think should be higher by that distance) it will drop approx 10deg and then will gradually start to rise up again and will eventually reach 90deg, once engine up to temp the heaters are red hot and even when warming up the fuel efficiency doesn't seem to be dropping off
Could this be the thermostat starting to fail?
Any help would be greatly appreciated


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[steveq]

Hi,

I am having much the same issue with my W204 C220 CDI with 56K miles for the last week or two.
The temp goes up to normal (just under 90deg), then drops back to 75 or so then slowly gets back up to the normal.
I suspect that it is the thermostat that is starting to fail but it could be the water pump. The water pump has a thermal coupling which might be causing this (I think).

On a previous Merc the thermostat went faulty but the symptoms were that the car never go up to normal working temp. I replaced the thermostat and all was perfect.

 

[C220jim]

I've replaced the thermostat the other day with a genuine one, still doing the same if there is a thermos coupling on the water pump is that something which can be replaced separately or is it a complete water pump assembly?


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[steveq]

The symptoms I am experiencing (and sound very similar to yours) are very different to what I noticed on my previous Merc -- car never got up to the correct temp and stayed at around 60 deg. That was solved by replacing the thermostat.

It is very frustrating for you to have replaced the thermostat and the issue persists.

I believe that the water pump must be replaced as a unit. I found a YouTube video of it.
Here is the link: https://www.youtube.com/watch?v=02qMFn91jV8

By the way -- how was the job of replacing the thermostat?
I looked at it and there appears to be a lot of ancillary items that need to be removed to get at the thermostat.

 

[C220jim]

Hi steve wow thanks for fast reply, the thermostat took me about an 1 1/2 to replace its a bit fiddly with the rear and bottom hose depending how the spring clips are, if you haven't got some spring clip pliers I would invest in some think I paid about £25 for a set of them, the air intake pipe and the belt cover come off easy enough for that little bit extra room I'd take out the oil filter and out some rag in the housing
Luckily i get on well with the pets guy at my local dealer I have emailed him this morning with the symptoms we are experiencing and he's gonna wave the email under a master or senior techs nose and ask him for a bit of assistance
The water lump and new aux belt aren't too expensive either although a do get a bit of discount but the water pump is done on an exchange basis which helps keep costs a bit cheaper


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[C220jim]

Steve, coolant pump switchover valve mean anything to you?


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[C220jim]

I've replaced the thermostat the other day with a genuine one, still doing the same if there is a thermos coupling on the water pump is that something which can be replaced separately or is it a complete water pump assembly?


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Steve
Has your alarm been going off at all? Mine has just started to do so, I am wondering whether battery voltage could be an issue....


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[steveq]

Steve
Has your alarm been going off at all? Mine has just started to do so, I am wondering whether battery voltage could be an issue....


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Hi, I haven't had any other issues like alarm going off.
Regarding the coolant pump switchover valve -- I haven't heard of it before. I presume it is the device that triggers the water pump to actually pump water.
These OM651 engines are complex.
I have noticed that the car loses some coolant - maybe a pint every couple of thousand miles. No obvious signs of coolant around the water pump or anywhere.

 

[C220jim]

Hi, I haven't had any other issues like alarm going off.

Regarding the coolant pump switchover valve -- I haven't heard of it before. I presume it is the device that triggers the water pump to actually pump water.

These OM651 engines are complex.

I have noticed that the car loses some coolant - maybe a pint every couple of thousand miles. No obvious signs of coolant around the water pump or anywhere.

I've ordered a new water pump and valve as a precaution although it's not overheating it's doing my head in as I know it's not right, but will check battery voltage as a precaution before I start replacing either pump etc
Is yours still playing up?


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[steveq]

Hi,

I have been paying more attention to the temp gauge recently.

I did a 10 mile trip yesterday. The temp gauge went up to about 80 deg after 4 or 5 miles, then fell back to 70 deg, then climbed back up to normal (around 90 deg) by the time I stopped.

The way the temp gauge falls back to 70 is a new feature.

My experience with thermostats was on my previous W211 which had more severe symptoms. The temp never got above 60 deg. I replaced the thermostat and the temp went up to normal very quickly and never budged.
Actually I did also subsequently change the water pump on that car but that was due to a noise from the front of the engine which I traced to the water pump bearing. The car had about 120,000 miles on the clock by that stage.

The symptoms on my W204 are different and sound similar to yours.

Maybe it is the coolant pump switchover valve?

Is your car losing any coolant?

 

[C220jim]

I'm not loosing any coolant ATM and there are no fault codes stored either this is a very strange one Mercedes have suggested water pump hence ordering one but will check battery voltage as that could and it's a long shot be the issue I shouldn't think yours is the original battery like mine?


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[steveq]

Hi,

I checked both batteries (the big one under the bonnet and the small (stop/start) one in the boot) and they are both badged Mercedes.

I only have the car just under 2 years so I can't be absolutely certain that they are the originals but I would be 90% sure. I certainly haven't changed either.
The big one under the bonnet was reading 12.35 volts when I checked just now and I haven't used the car since yesterday.
What does yours read?

 

[C220jim]

I haven't drop tested mine but I loaded up the hidden screens within command as it will show you battery voltage, mine was reading a low 12v but defo was charging so I will put the battery tester from my work on it first thing in the morning.. I'm still thinking water pump is a possibility as the pump could be stuck engaged and therefore over cooling but an expensive thing to replace on a whim


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[C220jim]

Hi,

I checked both batteries (the big one under the bonnet and the small (stop/start) one in the boot) and they are both badged Mercedes.

I only have the car just under 2 years so I can't be absolutely certain that they are the originals but I would be 90% sure. I certainly haven't changed either.
The big one under the bonnet was reading 12.35 volts when I checked just now and I haven't used the car since yesterday.
What does yours read?

Steve, checked my batteries today on the tester at work and they are both fine state of charge was ok on the big battery too, tomorrow is d day I'll either make the call to do the pump or I'll replace the valve and go from there will let you know what I find


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[steveq]

Hi,

Any further developments?
I noticed that you had started a new thread regarding your temp gauge dropping when you drive hard. I tried that on my car but it didn't seem to effect the temp gauge (maybe my definition of booting the car is different to yours though).
I think you said that you changed the Coolant Switchover Valve but that didn't resolve the issue.

Did you replace the water pump?

Thanks,
Steve