Do you know what your describing? The coolant reservoir is in the left hand guard with a little funnel sticking out, same as GC8 WRX.
That tank forward and above your manifold on the right is the header tank and is part of the cooling system, its not a reservoir. If the cap on the header tank has a damaged seal you need to replace it as this has probably bypassed and pumped all the coolant out as soon as the system built any pressure.

Just to clarify, you check your coolant level by looking at the level in the reservoir, not by opening any pressurised caps, they should only be opened to replace coolant or carry out repairs, or as in your case it has lost all its coolant and you need to refill it.

Buy a new cap if the seal is stuffed, take it to Auto One and get them to match it if your not sure, flush out the system, bleed it up properly, and try and see if it's still using coolant.

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Its just the internet dude, its not real.
F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i

hey guys thanks for all the help
i sorted it out yesterday all it was, radiator cap was rooted so replaced with new no more over flow..
took her for a long drive yesterday not one drama..

thanks for all the feedback very helpfull

Get the boost back up to stock boost levels. No need to drive around at nearly half stock boost level.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]

Bumping this for quick opinions.

After my first few laps out at collie today, while cooling down my coolant overflow bottle overflowed and spat a bit of coolant everywhere. I checked my gauges and it was still reading on the low side of the good area. I kept a very close eye on the temps for the rest of the day and it never looked to be getting above normal.

However, whenever I pulled in to cool down the overflow bottle was full to the brim and looked like it was bubbling away. I checked it before the event and it was midway from the high and low levels.

Anything to worry about?

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Twin scroll Pig Bi-Squeeling

if it continues to happen, headgasket or a dicky rad cap.

if its a once off- wouldnt worry about it.

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Long live the WRC

I would be replacing the cap first, or at least get it tested before jumping to the conclusion that it's the head gasket.

Generally if it's a head gasket the temp will skyrocket as soon as you start hammering it so probably pretty safe that it's just the cap or something small.

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Beaten up old 98 Gen 2 Liberty, 13.0, stock V3 STI running gear.
07 Transit motor home
69 VF & 70 VG Valiants needing full restoration
Yamaha Zooma 50cc rocket hopefully going with the Transit.

What model car do you have mate. Every time i do collie, or any hard driving, both my current car and my old one will empty the overflow bottle, making it go all over the battery area. I think in gc8's it is the design and size of the overflow bottle, combined with the cornering g's

Anyway, as said above. if it is a head gasket you would have known about it very quickly with overheating, even if it still had coolant in it.

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Version 6 STI

It's an 06STi. It didn't overflow until I got back into the pits. I had 5 or 6 more runs after that and it didn't overflow, the bottle was very close to it though. No problems on the drive home and looks back to normal now. Guess it's nothing major. Perhaps look at a new radiator cap.

Cheers folks.

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Twin scroll Pig Bi-Squeeling