air bubbles in overflow on shutdown

[Greg5OH]

wondering if this might be a small hg leak? when i **** the truck down i can see little air bubbles slowly bubble up in the overflow from the radiator. TBH the overflow has been low forever and i never got around to filling it, could it just be sucking air when its cooling off, then slowly burps the air when its warm? i hasve yet to check it when actually running, and i should probably fill; that oerflow to confirm and do a leakdown check. Just had some free time and figured id ask!

 

[chris142]

bad cap?

 

[79jasper]

I would fill it up cold, then see.

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[Greg5OH]

yes, really i should fill it first then ask question. Cap should be good, got a new one last year and trested it not too long ago.