M270 1.6 petrol whining noise and overcooling engine

[Daniel@1]

Good morning everyone and thank you for having me on board!
I own a B Class B180 M270 1.6 Petrol 2012 plate, which I bought 4 years ago, I did 70k miles without any problems( apart from the one listed below). Used only MB oil every 7k miles. The car has 126k miles now. Around 90k miles started to do like a whining noise around accessories belt area and engine overcooling ( more than 30 min time to heat up, and temp gauge dropping from 90 degrees to 80-60 then back to 90 dependingon the speed). Had the stat changed at that time, which didn't get the problem solved. Now the whining noise is getting worse and and engine overcooling too. Suspecting the fail safe vacuum valve from the water pump for the overcooling problem and the noise probably an bearing from the water pump.
Coudnt find any posts yet!
Did anyone had a similar issue and get it sorted?
Thank you!

 

[ajlsl600]

Moss behaving cooling fan?

 

[Daniel@1]

The cooling fan works fine, kiks in only when the AC is on or when the engine heats up! the car would overheat if the fan would not work, plus it will bring a fault code if it wouldn't work.
Just thinking the stat is ok since the return hose from the radiator is cold until about 80 degrees or so, and the hot air inside the cabin is ok too. On this engine the water pump is controled by a vacuum valve which stops the water flow until the engine warms up. From what I have read it also has a fail safe mode which, in case that something goes wrong with the pump ( whining noise in my case, which I belive is from the water pump) the vacuum line will keep the flow continuously open to prevent overheating and for this reason the engine will warm up slower than it should.
Not sure if I am right, I might be wrong, that is why I am hoping that someone else had the same issue and got it sorted by replacing the water pump. The pump is quite expensive, and I dont want to replace the original one if there is nothing wrong with it.
The whining noise from accessories belt area is gone once I remove the belt, the idler pulley, the tensioner and the belt are new. The alternator pulley works fine, spinning one direction only if I block the rotor, and the noise doesn't change if I swich the ac on and off so the ac compresor works fine. Unable to check the water pump, couldn't find anything onlyne that shows how to test it, it is a very unusual water pump ( pic below)
Thanks
Dan