i have 2001 c5 . i have prolem with expansion tank . have replaced but still loseing water (about 2-3 ltrs every 100 mls)
also tried replaceing pressure cap twice.
not leaking any where else only around cap/tank area

clowesy65, December 2007

It sounds like your C5 has excess pressure in the cooling system, if the coolant is still spewing out if you've replaced the cap. I would suspect cylinder head gasket problems which would cause this. Ask a capable garage to 'sniff' the air above the coolant with a gas tester - this immediately shows if there are any gasket leaks. Water pump leaks also aren't unknown on these.

John, December 2007