Waterworks

[Snakehips]

Good evening and a happy bank holiday to everyone. Can anyone shed any light on my waterworks. My water level in the expansion tank on the top mark then after a run out my water level has dropped down to the bottom mark then after another run out it is back to the top mark.i dont appear to have any leaks but I cant figure out what is happening. Any information would be much appreciated. Thanks snakehips

[Gaz mr-s]

It is a bit of an unnatural-wonder. For a trend, look at it when cold.  Sometimes the o rings on the radiator valves can let air in, it's believed. Undo a few frunk clips on the left corner as you look & burp the radiator when it's hot. Does your rad' get hot both sides?  If you get a good burp of air repeat the process next time it's hot. If you get air, do it again.  If you have air it will affect the tank level.

[Ardent]

Not uncommon.

They can appear to have a mind of their own.

Monitor for now. Burp it as suggested.

[Snakehips]

Thanks gaz radiator is ok hot on both sides Ive tried burping it i do  not appear to have air in the system no leaks
or overheating. I just don't understand it.

[Gaz mr-s]

Thanks gaz radiator is ok hot on both sides Ive tried burping it i do  not appear to have air in the system no leaks
or overheating. I just don't understand it.

Just be grateful then.   

[Jay]

Shouldn't be anything to worry about, quite normal behavior.

It's just the coolant expanding and contracting due to heat (the bottle is called a expansion tank for this reason).

So long as it returns to the same level you can relax.  If topping up is required it could signal a few things so you're right to keep an eye on it 

[Joesson]

To my thinking the system contains a volume of water that does expand and contract according to it's temperature. While I have experienced the yo yo effect described, more recently after a good flushing of the system, when I measured the actual volume of fluid in the system and then refilled with all but  half a litre of the determined quantity and then ran the car a few mile I found that the last amount would go in. Since then the level has consistently remained   around the maximum level.
My conclusion is that the system is prone to entrap air and careful, persistence can get it out.

[Dev]

All that is needed is to fill the coolant when its cold to the proper level. The expansion tank will go up and down as a normal process of operation due to expansion of the hoses under 1 bar above atmospheric pressure to raise the boiling point. The expansion tank also serves another purpose and that is to filter out any air in the system.

 If there is any suspected coolant consumption it should read when the car is cold as a base line of comparison.