Coolant level drops when engine running?

[Teg]

Took a short drive in the S2 today.

Had the coolant level light come on. Whilst the engine was on I checked the coolant level, it was too low. But when I turned the engine off it rose back up to the correct level.

Whats causing this? is something blocked?

Thanks

[Monkeymagic]

Technically as the pressure rises the level will drop very slightly. And rise once cooled. However if it's a considerable amount it may indicate exhaust gas getting into coolant.
With cooling problems I'd do a pressure test on a cold engine checking for external leaks.
Then I would do a sniffer test following the instructions to see if there is any indication of exhaust gas getting into the coolant.

[Teg]

Thanks for this. Yes its a fair drop. So would that mean the head gasket is going?

Thanks

[Monkeymagic]

It may be an indication. Do a sniffer check and take a systematic approach.

[Teg]

Just checked, the coolant smells a bit like its burnt? guess that is exhaust fumes.

Its not blowing steam or blue smoke out the exhaust.

[Tony Stark]

If it fails the recommended 'sniff test' remove the spark plugs and lay them out in order 1-5 to see if you have an odd one out looking at their colours. Its not imperitive but good to know which cylinder has the issue before any major work should it come to it.

How does it start and run initially after being left over night? (with pressure in the cooling system).