should'nt be asking this really due to run my own garage, but i've been having prob's with mt 06 2.5 hawk eye, drive normally all is ok , drive like a loon and the reserve tank fill's near to top of bottle, i've blead system and done a block test for head gaskets all ok, i did find the header tank cap wet at top leaking through the rivet on top of cap so replaced this , i've now found the rad cap doing same thing, so i've orded new for this. do you agree that if the cap is leaking slightly it won't be causing vacum to suck back coolant out of reserve tank when needed,engine never overheats and runs sweet, just level in reserve gets high and dose'nt go back down till i do it manually, the header tank is abviously low when this happens. and also do you top header to top or do you leave a little room for expension of coolant ??? any answers would be a help cheers . think i just need to replace rad cap,

 

I have been suffering this EXACTLY for the last 18 months and has been particularly bad recently.
I had to pour the expanded coolant back to the header tank, otherwise it would overflow and the heater matrix would gurgle a lot.
My header tank cap was originally faulty but recently the radiator cap was also faulty - I could hear air being sucked through the top under the label, when the engine was cooling down.
The other problem was the top rad hose had no rigidity to recover the expansion water through syphoning.
Turns out my top hose doesn't have a sleeve on it compared with all other newage cars I've seen.
I believe the sleeve acts to stiffen the hose and allow expanded coolant to be sucked back.
I've just changed the rad cap and top hose and things are back to normal.
Mines an 06 STi.

Nick

 

cheers for the feed back butty , i'll try a new rad cap cause it's leaking like yours was ' my pipe has a sleave so i'll leave that for the mo. any more problems i'll be back for more advise .


Rick

 

mine was the same once. normally the level should rise when the engine is hot and then the cap sucks the water back in when the engine cools.
once coming back from wales i drove the car like i stole it for a long time and the level went very high. i had to transfer it back manually just that once.
i have since chnaged the top hose as it had swelled a lot and had the beginnings of a split. it could just be me but the water seems to be sucking back in much better now.
not had any problems since.
check your top hose is not wider than normal, i,e compare it to the bottom one in diameter when hot or look for it balooning past the hose clip in the middle.