I have a water hose that leads from the engine on the right side to the radiator, this keeps pressurising, if I loosen the top of the water bottle the pressure drops and the pipe is as normal, it will sometimes activate the coolant required notification as the bottle is empty until the pressure is released then it refills, to ups are required though at least once a week. This has started happening after what seemed to be pieces of a gauze filter were floating in the water bottle

 

When the engine is at operating temperature it is normal for the cooling system to be pressurised. If it was not there is a leak. The coolant pipes should feel hard with the engine up to temperature. There is a pressure release valve in the coolant bottle cap that prevent over-pressure.
The coolant level should not change in the way you have described.
I think you have air trapped somewhere and need to bleed the system.

 

Thankyou for you response, the only thing that is of concern, it's the fact that the coolant fluid low warning appears also

 

If you are adding coolant then I guess you have a leak....
The fun is finding it.....

 

Only when the bottle is low. When I've looked at the bottle when the warning has appeared, the bottle can be empty, when left to cool and then release the pressure the bottle will refill, also the pressure can still be there 5/6 hours after the engine has been off

 

So the coolant bottle empties when hot then refills as it cools ?
Is the coolant temp gauge stable at about 80C when driving ?

 

Yes that's correct and the gauge is always steady at approx 80

 

I cannot visualise that unless there is air trapped in the system, otherwise there would be no where for the coolant to flow to.

The w211 requires bleeding with special tools when the coolant is replaced.
So I know exactly which car you have : what's your vin ?

 

It is a bit of a puzzle.
YK11 LYA.
out of curiosity, do you think that if the gauze filter had broken into small pieces, they could of been pulled through with the water and created a blockage somewhere around the engine

 

So you have a W212 with a OM651 engine.
If there was a blockage then you would have coolant temperature issues.
The WIS has a complex vacuum method for draining and refilling the coolant !!
I suggest you go to MB or an indy, depending on the depth of your pockets, who can do the procedure properly

 

Thankyou very much for your time and input, I'll call at a couple of outlets and get prices, thankyou again
ian