Temp Gauge fluctuation warm up from cold start

[Lafetoo]

I am newbie here, just bought a 2015 E250 CDI FL(om651), my temp gauge has shown fluctuation symptom during first 15-25 minutes (15-20 km) of warm up, which goes up to 82 then drops back to 70 for 2-3 cycles before stick with 90 degrees, been searching weeks without a clue, dealer has changed thermostat under warranty but make no difference, dealer comment this is "normal".
I owned numbers of vehicle before, none of them behaved like this and took this long to reach optimal temperature.
Can anyone share their experience or is it really consider "normal" for mercedes CDI engines? or any fix /solution?
Many thanks

 

[Daveuk]

My heaters blow warm really quickly but I can also drive a fair distance before the temp gauge gets right up it usually sits on 1/2 for ages even in summer it’s done this but then I wonder if it’s because the cars under no load and cursing at 60mph at 1500rpm on the runs where I’ve noticed it.


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[whitenemesis]

You may have a supplementary electric heater which will heat incoming cabin air until the coolant is warm enough.
You may also have a failed coolant thermostat, engine should reach operating temp eventually no matter how much "cursing" one does!

 

[Daveuk]

You may have a supplementary electric heater which will heat incoming cabin air until the coolant is warm enough.
You may also have a failed coolant thermostat, engine should reach operating temp eventually no matter how much "cursing" one does!

It does get to temp eventually I’ll see how long it takes next time I drive it.


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[grober]

The OM651 has a switchable clutched waterpump[ electrically controlled-pneumatically operated iirc] it can be switched off to help engine warmup after a cold start- perhaps this is what you are seeing? ps they known to go faulty
http://autocats.ws/manual/sdmedia/mediadb/mb_Acrobat/einf/204/einf_br204_cdi_OM651__en.pdf

 

[Lafetoo]

I beleive a faulty water pump will most likely cause overheat or coolant leaks, have no idea if it may cause temp fluctuation durimg warm up period. CMIIAW.

 

[grober]

Water pump failure

 

[Lafetoo]

Water pump failure

The car has got no overheat issue, only fluctuates below 90C during warm up from cold start.
Do you mind to elaborated more detail how an water pump failure will cause this? Please.

 

[grober]

Post 4 on that link I posted describes very similar symptoms to the OP's symptoms.The pump isn't failing but might be switching on and off initially as the engine warms up??

 

[Lafetoo]

I see, wondering how do I convince dealer to do a warranty replacement as it has no sign of overheat and leaks.

 

[grober]

AFAIK there is no formal documented MB recall for these pumps altho the problem is known, and at over three years old the car will be out of manufacturer warranty. It might be the pump or its controlling circuitry- an electrical fault should show up with a fault code but anything pneumatic won't. Your dealer is either unaware of the pump problem or refuses to acknowledge it. I can only suggest that you approach them again and see if they will share the cost of a replacement/repair?

 

[Fununcle]

Had the coolant pump replaced on my 5 year old c180 free of charge by mb earlier in the year, it is a known problem on those engines, maybe is on yours too?

 

[Lafetoo]

Had the coolant pump replaced on my 5 year old c180 free of charge by mb earlier in the year, it is a known problem on those engines, maybe is on yours too?

Did your car had the same symptom as mine before the water pump changed ?

 

[Fununcle]

No, none at all. Had to go to mb for the airbag recall and was asked if they could keep it to change the coolant pump, it was weeping apparently and the failure of them is a known problem. Dont know if this is the same on yours but hope you get it sorted.

 

[Lafetoo]

No, none at all. Had to go to mb for the airbag recall and was asked if they could keep it to change the coolant pump, it was weeping apparently and the failure of them is a known problem. Dont know if this is the same on yours but hope you get it sorted.

Thanks for your advise, will post update when I get this done.

 

[Daveuk]

I am newbie here, just bought a 2015 E250 CDI FL(om651), my temp gauge has shown fluctuation symptom during first 15-25 minutes (15-20 km) of warm up, which goes up to 82 then drops back to 70 for 2-3 cycles before stick with 90 degrees, been searching weeks without a clue, dealer has changed thermostat under warranty but make no difference, dealer comment this is "normal".
I owned numbers of vehicle before, none of them behaved like this and took this long to reach optimal temperature.
Can anyone share their experience or is it really consider "normal" for mercedes CDI engines? or any fix /solution?
Many thanks

I watched mine the other day when I left work it’s a steady climb to normal temp but took about 16minutes till it was at normal temp but car wasn’t under any load and sat at 50-60mph


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[DrNick]

My 2014 E250 petrol (so not a CDI) had a failed water pump (symptoms, car overheating randomly - there's a thread on here about it). When it was replaced it cured the overheating, but since then I've noticed that it does the same as yours, in that it can go up and down a few times before it sits at the 90. I was just thankful it was no longer overheating so am not concerned.

The cooling system on mine is complicated and I suspect as yours is the same vintage, it is too! There is a valve on the water pump that is used to stop water flowing until things have started to warm up. This is before the thermostat has a chance to get involved. There is also (apparently, though I've never looked) a vacuum operated shutter system that shuts off airflow to the radiator. To add to the complexity, the thermostat is electrically operated, in that it appears to have a heater in it to trigger its operation. All this is there to give a speedy warm up, but makes for a complicated control system. I was assuming that there was a learning system in place where it learned the best times to operate the various 'features' to give best warm up, and so after the overheating failure, all these parameters were all out of whack so the control algorithm would have to relearn it. I havn't looked recently so I don't know if it still does it.
Has it had any work done on the cooling system before you got it?

Alternatively, one or more of these devices may be sticking. For example, at start, all valves etc may be closed, engine starts to warm up quickly, controller tries to open a valve a bit to adjust something, valve doesn;t move, controller tries a bit harder, valve eventually pops open, cold coolant flows, everything cools down, controller backs off valve, doesn't move, backs off a bit more, closes, coolant warms up quicker etc, until when its fully warm, all cold start mechanisms are off and the thermostat takes over. If that's the case, lets hope they eventually fail in the open position. At least then it won't overheat!

 

[Rory]

I watched mine the other day when I left work it’s a steady climb to normal temp but took about 16minutes till it was at normal temp but car wasn’t under any load and sat at 50-60mph

On a chilly day mine takes 15 miles (20-25 mins) in that kind of flowing A road driving to get fully warm.

OK, it's a much older car etc, but wife has a VW Tiguan with their latest 2 litre deisel. Hefty electric heater will blow warm air near instantly, water temp shows 90C in 3 miles. But the reading is a "lie" - it's fed from the ECU and it's basically just saying "normal". However the cluster computer will show the oil temp. That takes about 4 miles to even register (at 50C). You're into the mid-teens on miles before the oil temp is also 90C.

 

[DrNick]

My 2014 E250 petrol (so not a CDI) had a failed water pump (symptoms, car overheating randomly - there's a thread on here about it). When it was replaced it cured the overheating, but since then I've noticed that it does the same as yours, in that it can go up and down a few times before it sits at the 90. I was just thankful it was no longer overheating so am not concerned.

The cooling system on mine is complicated and I suspect as yours is the same vintage, it is too! There is a valve on the water pump that is used to stop water flowing until things have started to warm up. This is before the thermostat has a chance to get involved. There is also (apparently, though I've never looked) a vacuum operated shutter system that shuts off airflow to the radiator. To add to the complexity, the thermostat is electrically operated, in that it appears to have a heater in it to trigger its operation. All this is there to give a speedy warm up, but makes for a complicated control system. I was assuming that there was a learning system in place where it learned the best times to operate the various 'features' to give best warm up, and so after the overheating failure, all these parameters were all out of whack so the control algorithm would have to relearn it. I havn't looked recently so I don't know if it still does it.
Has it had any work done on the cooling system before you got it?

Alternatively, one or more of these devices may be sticking. For example, at start, all valves etc may be closed, engine starts to warm up quickly, controller tries to open a valve a bit to adjust something, valve doesn;t move, controller tries a bit harder, valve eventually pops open, cold coolant flows, everything cools down, controller backs off valve, doesn't move, backs off a bit more, closes, coolant warms up quicker etc, until when its fully warm, all cold start mechanisms are off and the thermostat takes over. If that's the case, lets hope they eventually fail in the open position. At least then it won't overheat!

Noticed this reads like I think I'm describing your system. I'm describing my system. I've had a look at the link a few above that describes the features of your engine, and it is a bit different. It still has the electrically heated thermostat, but no radiator shutters and no actual valve in the water pump. It does however, have a vacuum operated shutter in water pump which achieves the same thing, which others have pointed out.

"The coolant flow can be stopped by vacuum via the switchover valve of the coolant pump, which is located on the left on the throttle valve actuator. In this case,a regulating valve slides over the impeller, thus closing the coolant feed" (taken from link a few above)
Sounds to me like this could be the culprit.

 

[Lafetoo]

Noticed this reads like I think I'm describing your system. I'm describing my system. I've had a look at the link a few above that describes the features of your engine, and it is a bit different. It still has the electrically heated thermostat, but no radiator shutters and no actual valve in the water pump. It does however, have a vacuum operated shutter in water pump which achieves the same thing, which others have pointed out.

"The coolant flow can be stopped by vacuum via the switchover valve of the coolant pump, which is located on the left on the throttle valve actuator. In this case,a regulating valve slides over the impeller, thus closing the coolant feed" (taken from link a few above)
Sounds to me like this could be the culprit.

Thanks DrNick, very detail explanation.
Yesterday, I found that the coolant temp behaved normal again without fluctuation issues, I started the car from cold drove 3 min to pick up something and stop the engine for 2mins while waiting, the temp was just like <40C, then start the engine and go straight to motor way for 40km, the gauge go steaily to 90C without fluctuation.
Second attemp, parked 4 hours later, on return trip start the car at temp again <40C, same thing happened steadily to 90C without fluctuation.
I guess there must be something within the cooling system algorithm!
Guess the system tries to enforce the thermostat to open at around 82C if the delta temperature is greater to certain amount , to avoid too cold coolant flush into hot system, that makes the fluctuation, it just my guess.!
Will observe few more days.