When I boot it my coolant temp drops on my gauge (c220 2011)

C220jim

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Jul 21, 2017
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30
Car
2011 c220 Amg
When I accelerate hard and then coast or slow down to normal speed my coolant temp seems to drop off on the gauge any help would be great
I've already changed the thermostat and changed the coolant switchover valve


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ivan1983

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Aug 21, 2012
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Middlesex
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R129 500SL, W140 S500L, R170 230K, 530i Touring, ZZR 600 W126 380SEL now gone :-(
Does it ever get too hot, I had a car where the water pump was on its way out. It would slowly start to creep up in temp, to keep this under control I would drop a gear and let it rev high which would bring the temps down....
 
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C220jim

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Joined
Jul 21, 2017
Messages
30
Car
2011 c220 Amg
The temp may have crept up a couple of degrees, but I took it out earlier and it's dropping off slowly even normal driving, it's almost as if it's cooling too well ....


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LvR

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Apr 18, 2014
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55
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South Africa
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A160 W168
What is the real-time info on STAR like for the engine while driving?

You can see exactly what the temp (and a horde of other parameters) is doing and whether the ECU is the culprit (activating coolant valve for no reason) or some other mechanical issue is in play.

If its over-cooling the thermostat is definitely part of the problem imo ................... it may be new but it could be out of spec or faulty.

I would start with STAR..................
 
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C220jim

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Jul 21, 2017
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30
Car
2011 c220 Amg
I don't have access to star so I guess it's a dealer job?


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LvR

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Apr 18, 2014
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South Africa
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A160 W168
I guess.

I don’t know how sensitive and accurate the in dash temp meter indication is on that particular set-up ............... and also how the ECU has been told to control the cooling fans (STAR).

On my W168 I can for example set the slow and fast running cooling fan speed switch points individually and in quite a wide range - now depending on how sensible the points are chosen, I could easily cause your observed cooling gauge behaviour on my vehicle if I wanted to.

I really do think somebody needs to speak to the car via STAR and then interpret what you are reporting while looking at real-time values.

Also ....................

When I accelerate hard and then coast or slow down to normal speed my coolant temp seems to drop off on the gauge
That is a very subjective statement and may actually be totally normal behaviour imo - eg - if the gauge is quite sensitive and accurate, I would say it could be absolutely normal if there is no tight integration of the pump switch point and thermostat temp as long as the temp doesn’t drop far (more than about 5C?) below the thermostat regulating temp.

If this bothers you a lot I suggest get a cheap Bluetooth OBDII dongle for the car and make it talk to your cell phone via cheap software like Torque Pro in order to do some of the stuff STAR can do - with it at least you have access to the actual ECU's temp signal rather than the dash temp gauge signal that is often separate
 
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C220jim

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Joined
Jul 21, 2017
Messages
30
Car
2011 c220 Amg
The thing is this isn't normal behaviour for the vehicle I pay attention to my gauges probably more than I should but this issue has recently developed, I guess it's time to book it in with the dealer and hope they can find something, the temp is clearly dropping on the gauge not instantly but progressively drops and then will gradually rise back up, this sort of fluctuation isn't normal for the car
I've read real time ect but unfortunately wasn't able to get the car to fault whilst the reader was plugged in


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