Rover V8 Overheating - Expansion tank dry

[Chuck21]

Hi folks. My buddy has a Cobra rep on a Rover V8. It overheated on a drive, no issues driving but water temp through the roof. Took a look and no obvious leak but expansion tank dry. Is most obvious issue a minor leak from a hose or similar that wasn’t noticeable as it would just evaporate in/from the engine bay?

Any advice welcome, thinking we just fill up from the header tank, start her up and watch for leaks?

[paintman]

When was the coolant checked before the overheat? Would give some idea of how fast the water loss has been.

Be an idea to pressure test & see if there are any visible leaks.

Problem when hot is that any small water leakage may evaporate instantly.

FWIW I've just dealt with one on my RRClassic V8.
Pressurised the system cold to 15 psi using one of the vacuum/pressure pumps (I've got a mity vac hand operated vacuum/pressure pump) & watched for leaks.
Turned out to be a hoseclamp on the water pump to inlet manifold hose needed tightening.

Hopefully yours will also be something simple & not a HG.

[Chuck21]

Thanks Paintman.

We drained it from the rad bottom hose (not a lot came out) and re-filled then ran it for a good while. There was the odd spike but overall it stayed in range. As you say I think the next step is to fully pressure test to make sure there aren't any other issues.