subaru coolant expansion tank problem

[andycook]

Hi
- not a 4runner issue this time, but my subaru forester.

I always keep an eye on coolant levels in both cars - radiator and expansion tank.
recently in the subaru after long drives, when its cooled down, the coolant level in the expansion tank reamins high. Its not been overflowing.
And when i take off rad cap, the coolant level is low!. I have to draw off coolant in the expansion tank and this fills the radiator level back to correct level.
i have put a different rad cap on, and same issue.
there is no gush of air trying to get in the radiator when i remove it, so its not under vacuum, the top hose isnt collapsed on cooling.
the pipe to expansion tank isnt blocked!

So am I right in guessing there must be a leak, so air is being sucked into the system on cooling, and not sucking coolant back in from the expansion tank?

oil isnt milky and no sign of oil in the coolant,

a strange one!

[darkdezigns]

my money wud be on thermostat sticking

[andycook]

cheers breakdowntruck2 -

out of interest - mechanically how would a sticking thermostat stop the coolant draining back into the radiator from expansion tank on cooling ?

and explain the apparent vaccuum on cooling and coolant contraction - being lost?

i also managed to find some air in the system, by burping the system, i could hear the air bubbles being released from somewhere and bubbling up through the radiator

[Garygadget]

have you checked the inlet and outlet on the expansion tank ...1 or other could be blocked ??

[charvell]

sorry for being dim today, are you loosing any coolant? and is it smokey from the exhaust ?

[darkdezigns]

thermostat sticking,wud cause pressure to build when hot,and drop when cold,u would prob find if u sat in traffic it wud overheat,but not all the time yr moving,