Expansion tank stealing water

[markcro]

My car is the exact same when on track. It can takes days or even over a week for the radiator to draw the coolant back in. But then I have to top up the expansion tank to make up for the coolant that spilt out of the overflow. But it has been like this for years now. Not a bother on the road. So I'll be interested in seeing what you find.

[skyshack]

Coolant overflow issues that only happen under high load are usually down to a cracked head. The crack only opens up when engine gets "fully" warm.

[markcro]

Is there any checks that can be done for this?

[green_rs13]

take the head off and have it pressure tested. although if its doing this then get a 'sniff test' done then you will know if combustion gasses are entering the coolant system, if they are then the head is coming off anyway.