Help please, coolant concerns

[steelnads]

Hi folks, My griff 500 engine has just undergone a rebuild following cracked heads. These were repaired but I am concerned because the coolant level drops in the expansion tank by 2 or 3 mm every 100 miles and also there are a few bubbles visible when peering in. There are no obvious coolant leaks.
Do you think I have a problem?

Thanks Steelnads

[JMorgan]

My symptoms before a major rebuild. Get it checked quickly. I had cracked heads but had them replaced not repaired. After my rebuild I have not topped up for 3000 miles or so. Loss maybe down to your system getting pressurized pushing water out. No expert but that's what my symptoms were and may not have anything in common with your problem.

[steelnads]

(How the hell do you measure it so accuratly anyway).
its easy when your paranoid
Thanks for the comments i will get it checked under warranty.