Bear with me while I explain this headache!

One issue I have with MY07 wrx 2.5l is there doesn't appear to be any flow from the coolant tank, air in the cabin is stone cold constantly and the inlet and outlet hoses that pass from the engine bay to the inside behind glove box are also stone cold.

Coolant clearly needs to be replaced due to a grey colour.

Now after burping the car for half an hour I went for a drive and had mildly warm air blowing for a minute until returning stone cold. when I got back and checked the coolant tank, the tank was literally brimming to the top.

I have heard possible HG, but I have no smoke and no overheating issues from the engine. the coolant appears a milky gray. there are no smells of coolant in the echaust or cabin suggested by a HG. also there doesnt seem to be any engine temp issues or overheating even after hard driving suggested by HG faliure.

There is very little info online about this problem with this model but someone must have experienced this and found a soloution.

Problems could be -
Air Lock,
HG,
Thermostat fail.

Please any advice would be greatful as its not nice in winter not having heating on tap and more concerning coolant isnt leaving the res and isnt flowing freely.

im thinking of draining the coolant and refilling the system but concerned ill be wasting coolant and the problem still exist. im sure a coolant change wont resolve this.

 

Wasting coolant? Its like a tenner.

milky grey is not good.

Ill put a tenner on headgaskets right now...

 

sorry what I mean more concerned wasting time flushing it to put more coolant in and create more issues with airlock as these pain for airlock apparently

 

Follow Alcazars method and you wont gonwrong.

takes 10 mins

 

So today I changed the coolant and a new thermostat, dodgy previous owner removed the origional thermostat, cleaned out the coolant res of oily residue built up in there, ill keep an eye on it in the meantime but there is now heating in the cabin, ill be ordering a gasket test to see if it is the gasket or not.

 

Air lock they are well known for it I would say head gasket is the bottom hose cold as well

 

Thermostat was removed for a reason

And to have oily residue tells me that combustion gases are getting in, which tells me hg fail.
A gasket test/block test won't always show unless it's past gone as only on idle.

Take it for a good *** blast on boost and check again, when on hard boost the gases will enter and if it does then...........well rebuild time.