W204 2011 Facelift OM651 - Temperature issue

[mrmb]

Hello Guys,
Today on the way to work, for the first time I have notice a longer time for the coolant temperature to go to its warmed position which is around 90 degrees. It took the car about 20km to reach that position and for the most time the temperature was stuck around 70 degrees. I will monitor this on the way back to home today afternoon. My questions is, could it be a thermostat that had a struggle to open, or it opened to early?

 

[mercedes13156]

Diesels are notoriously slow to heat up. Mine used to take about nine miles of gentle downhill driving before it was up to temperature, even in the summer. In the winter it took an additional couple of miles of getting up to 70mph to settle at 90 degrees.

If the thermostat was opening early, or stuck open, you'd probably never see 70 degrees, far less 90. If it was stuck shut, the oil would take the brunt of the heat and dissipate most of it through the oil cooler, however, in those circumstances, the engine might overheat.

On these engines, it's a relatively simple job to replace the thermostat.

 

[mrmb]

Thanks from the reply. I have checked that again when I was going back from my work today. Everything was OK, I think it was one time weird occurence, however I will monitor it for a while.

 

[Uncle Benz]

Do check your coolant level please. These engines are notorious for coolant leaks from both the plastic water pump and the coolant outlet on the cylinder head that holds the fuel filter. The position of the coolant temperature sensor means that if it runs low on coolant the sensor measures the temperature of the air above the coolant, and then reacts slower than if it was in the coolant itself.

 

[mrmb]

Hey UncleBenz. Thanks for the advice. I am aware about the leaks on this engine. After cold winter that we had in Ireland I have noticed that my coolant went down a bit. I went to the dealer, bought a bottle of their premixed coolant and topped up about 200ml. So far everything is fine with the coolant. It is about 1cm down the top black cover. At my friend's garage I have put the car on the lift to check for coolant leaks but I could not find anything.

 

[Uncle Benz]

Just shine a torch down near the fuel filter. The coolant leak from here pools on the top of the intake manifold and rarely shows a drip below. It tends to dry again with the residual heat after the engine is stopped, and leaves a white/green crusty residue.

The cooling system on these can be a bugger to bleed, and air can still be trapped even though the reservoir appears full. There is a star procedure to excercise various bits to purge the air out iirc.

 

[mrmb]

Thanks for the info. I have taken a look at the engine bay. I could not see any sign of the leak under the filter. I have the SD C4 Chineese clone for my personal use as mechanics in Ireland are useless and I can fix more myself than they can hahah. Would you be able to provide me that procedure just in case if I will be doing anything with my cooling system as changing the water pump etc. so I will know how to bleed the system right?