Has my HG gone?
 

Took the old bug out for a run today and it appears that the new radiator cap has not fixed my coolant issue so I think it could be a bit more sinister! What do you guys think?

Spec:
Forged 2.5 with cometic gaskets & ARP head studs, AVCS heads. MD321x turbo (T+) running 1.5/6 bar 440bhp
Symptoms:
Coolant in overflow rising after driving and not returning to original level on cooling.
Bubbles in coolant overflow tank when running (warm) and after driving for a few minutes.
Expansion tank level fallen once cooled - no loss of coolant it's all the the overflow just displaced by air.
No obvious exhaust smell in coolant, coolant looks slightly dirty but no oil film/ residue.
No obvious contamination of oil.
Possible slightly excessive moisture/steam from exhaust but car has been standing for over 2 months.
Car runs perfectly.

For piece of mind i'd get a sniff test

If coolant is being pushed into the plastic expansion bottle by the rad, other than the hot /cold level then you must treat as worst case (HG failure).
I had this but it started on track, after a few laps the bottle would be full.
If it is the HG it can get seriously worse with dire consequences for your engine.
Best to think the worst rather than hope it's not happening.
Trev

As above, any garage will do a sniff test. Doesn't cost the earth either.

How much if any do you have to top up the cooling system ?
As suggested above - get a 'sniff' test or a Cylinder leakdown test done on the engine.
How long ago was the engine built/upgraded.

Mick

bubbles in the overflow is not indicative of hg. this is normal in small amounts because when the water leaves the header into the recovery tube and overflow it changes from pressurized to atmos and boils giving bubbles.
This recovery system used on subarus is not brilliant - most car manufactured now use a half full pressurized header only now. e.g ford.
On a Subaru its usual for the level in the header to sit 15mm below the top as the recovery is never perfect. have you checked the recovery line for leaks/tight seals?

wouldn't the car be puffing put white smoke on start up ? or lose of power or are the subaru symptons different?

Engine has done around 14k miles and was built in 2010. The system doesn't need topping up at all, I occasionally reverse 'syphon' the coolant from the overflow back into the expansion tank to top that back up. I'll get the car booked in for a sniff and leak down test and take it from there.

it maybe just the gasket lifting under boost and not when driven off boost , I had this problem after my rebuild on a 2.5 , would only loose coolant under high boost but not normal driving !!

that's what started to happen with mine, but a few months down the line it died on the rollers and the whole engine had to be replaced. The cause was Hydraulic compression, when eventually the pressure from the cylinders, instead of pushing coolent out gets drawn back into the cylinder, the piston can't compress the liquid, so heads, block, piston, rod and crank take the hit.
Trev

yes either way its a engine out job...I've replaced it with a EJ22 2.35 forged ...heads are held down with RCM 14mm head studs so no chance of that happening again :)

moral of this story is do it once and do it right !!