Overflow tank acting weird

[vboyq]

hey everyone i have an s13sr20det in a s13 chassis, and the overflow tank stays almost at the "Minimum" line when its in the morning, after it has been sitting still all night and cooled off. But after a little bit of driving and the car warms up the tank rises with coolant almost to the "Maximum" line.is there a reason for this, is the car overheating, cuz i don't see the temp gauge move past the 1/4 mark EVER. as far as cooling mods i have about a 60/40 mix of coolant and water, a Koyo Aluminum Radiator, and a Permacool 14" electric fan thats wired to a constant on(i think its rated like 2800 CFM), and no fan shroud.i know the tank is supposed to fluctuate, but this just seems peculiar. it goes from almost empty to almost full

thanks, quang

[IveBeenBad]

it may be a bad thermostat... that tank is coolant overflow which happens when the coolant gets too hot and boils over

[Hijacker]

check your radiator cap and make sure it's not corroded (assuming you used the original cap).

[vboyq]

no i got a new cap.. i was thinking that maybe there is a air bubble trapped in there. not one big enough to over heat but, enough to "burp" the coolant out into the tank. wat do u think?