I have just changed my coolant and the expansion tank was empty. My understanding is that it's supposed to be half full. I disconnected the hose from header tank and attempted to suck out the old coolant but none was present so I added about a quart with a large serenge (spell check) . If I knew the capacity I could get it right without removing fender well.
Thanks

Jack

 

After a little research, it seems some call the header tank where you fill up system, (expansion tank). For clarity, I'm asking about the tank behind right front tire behind wheel well cover.

Jack

 

With a good torch you can see the level in the tank through gaps in the A pillar region when the passenger door (for LHD cars) is wide open. Last time I had the wheelarch liner off I added green and red tape to the tank wall that I can see from outside.to mark the level I want to maintain.

 

Thanks astromorg, I'll check it out.

 

Thanks again astromorg, I checked and can see it very clearly. I need to add a lot more as it looks as though it's almost empty. Makes me wonder how many of us are running around with empty expansion tanks wondering why low coolant light comes on so often when it only takes a touch of fluid to top it off.

 

overflow is supposed to be almost empty when it’s cold

end of thread

 

Rubbish ...half full is correct ..how can it suck back if its empty . The pipe up to the expansion tank needs to be full for the expanded coolant to shuttle back and forth.
and the liquid in the overflow tank allows air to come out the pipe and be replaced with fluid.

 

To understand how the expansion system works and includes some excellent ideas and guides view this video from O&DR Modurol
See here:

 

It only sucks back into the header tank what the system pushes into expansion tank as the engine heats up. If it starts empty with a cold engine it ends empty after a heating cycle. If it starts half-full it ends half-full. If you check that the header tank is full when the engine is cold and then check that it is still full after a full heat cycle, then the expansion tank has found its own level and is working properly.
"Rubbish" is best avoided unless you're 100% sure that you know what you're talking about. 😉
Richard

 

If the tank is half full it will take care of evaporation for a long time. If you start out with an empty tank the level in the header tank will go down just a tad every heat cycle. That is was what I was experiencing. Now my tank is half full. I'll keep and eye on the header tank for a while and see how it goes. Also, if there is coolant in expansion tank it will cool the hot pushed out coolant and slow evaporation I would think.

 

Indeed. With 50:50 coolant mix, several decades I would guess. 👍

Richard

 

Half full is correct . Your car do what you like.

 

Anything else would be a travesty of justice. 👍

Richard

 

According to Jaguar (JTIS) the tank behind right front tire is a "Degas bottle"
And the tank with the filler cap are indeed the Expansion tank.