Caterham expansion tank

[Connrod]

Hi
Wondering if anyone can advise I have a 2011 supersport ex racer I am getting ready for the road, it has the sigma 150 engine,is it normal for the expansion tank to fill when it has been running for some time it returns to normal once the engine has cooled down, not sure if this is a symptom of something else eg head gasket, but it's not showing any other symtoms

[Mr MXT]

Not a Caterham owner, but that’s the very purpose of an expansion tank isn’t it?

[Connrod]

Yes you correct but I've never seen one full when its running the level usually rises a little it may be how caterhams run as I'm not that familiar with them.

[Mr MXT]

My Duratec Westfield does that if it’s overfilled.

[Tazio77]

It may just be trapped air, and need bleeding