W205 c250d Auxiliary cooling pump

[jasper81]

Hi,
I have a 2016 C250d that keeps losing the coolant from the expansion tank on the passenger side of the engine bay. I beleive this is the turbo intercooler system.
I have replaced the pump as the initial one was broken. However after I vacuum fill the system it loses the fluid after a run, but the system remains pressurised (all the hoses are hard) until I take the cap off. When under the car you can unplug the 3 pin plug and re plug it back in and the pump seems to purge at full speed and the. Stop and pump slower. Sometimes
You can see the coolant residue around the tank, sometimes you can hear the cap passing as it’s relieving pressure and sometimes
There is no evidence of anything leaking.
Monitored the live readings today and the Inlet air temp stayed just above ambient , 3degrees outside temp circa 3-6 inlet air temp and the engine coolent stayed at 90 degrees on the 50 mile run. I have a new temperature sensor that fits in the line by the coolent pump hoping that this is not triggering the Pump to run to cool the charge air.
I can see loads of discussions on here so apologies if this is in the wrong place but can’t seem to find any diagnostics to confirm what to check next. Any help very much appreciated

 

[Oleks1992]

Hi,
I have a 2016 C250d that keeps losing the coolant from the expansion tank on the passenger side of the engine bay. I beleive this is the turbo intercooler system.
I have replaced the pump as the initial one was broken. However after I vacuum fill the system it loses the fluid after a run, but the system remains pressurised (all the hoses are hard) until I take the cap off. When under the car you can unplug the 3 pin plug and re plug it back in and the pump seems to purge at full speed and the. Stop and pump slower. Sometimes
You can see the coolant residue around the tank, sometimes you can hear the cap passing as it’s relieving pressure and sometimes
There is no evidence of anything leaking.
Monitored the live readings today and the Inlet air temp stayed just above ambient , 3degrees outside temp circa 3-6 inlet air temp and the engine coolent stayed at 90 degrees on the 50 mile run. I have a new temperature sensor that fits in the line by the coolent pump hoping that this is not triggering the Pump to run to cool the charge air.
I can see loads of discussions on here so apologies if this is in the wrong place but can’t seem to find any diagnostics to confirm what to check next. Any help very much appreciated

Charge coolers are known to leak internally, I'd take the boost pipe off the charge cooler and pressurise that coolant circuit and see if any coolant appears inside charge cooler

 

[jasper81]

Thanks for the response, I’m assuming the charge cooler is the rectangle box on the same side as the expansion bottle and under the expansion bottle and the oil filter. Looks a bit like the picture below.
The strange thing for me is the system hold a lot of pressure even when water has gone.
Will take the pipe off and take a look

Many thanks

 

[jasper81]

Hi I’ve removed the intercooler alloy pipe from the water cooled intercooler day that runs across the front of the engine, no water inside at all just a thin film of oil really. Changed the temperature sensor located in the pipe right next to the pump and refilled the system by vacuum filling. Pressure tested the system both hot and cold with no drop in pressure notes over 30 minutes. Purged the air from the system by pulling the plug off the pump connection and reconnecting this seems to start the pump on full speed and then it drops back, did that a few times and noticed that on key position 2 there is water flowing into the reservoir for a bit.
To be honest now I’m a bit lost as what to check next,
Did try to bridge the temp sensor plug to get the pump to run and and also when the pump was off the car tried to test it with 12v to the live and earth pin but no joy pump didn’t run on the bench or when bridging the plug, however when you plug the pump back on the car it starts up
Anybody have any ideas ??
I’ve changed the cap on the reservoir as well
Any help appreciated

 

[jasper81]

Did notice the temp sensor I got from Mercedes (£18) was a different number but this was the one for the location new one was A000 905 61 02 the old sensor was A099 905 3700 both say temp sensor but wondered why different numbers. Just as a heads up the intercooler pump is £110 exchange from
Merc so better than buying a second hand one