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Expansion tank/rad issue STi S202

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Easy guys I'd be grateful for any advice. Have looked about and have seen this issue on other forums but no solution is ever revealed. Just want to get it sorted early with minimum faff! :)

trying to keep it concise:


drove easy for 20 mins or so after a good warm up. Parked up no prob. Left it for half hour came back, warmed it up, easy driving then got into the motor way giving it some beans before I pulled intonB&Q


parked up got out and there was steam coming out the front with a sweet smell of anti freeze! Underneath of bonnet passengers side above the expansion tank seemed to be the most soaked with coolant, proper dripping from the right, but generally everywhere!!


called aa n the guy seemed confused. Took off the header tank cap and dos a pressure test. No leaking from anywhere, not the rad. Did it whilst engine on too, revving pretty high, no issues! 

Dried it up drive it home steadily, 20 minute drive with motor ways. Aa followed. Got back n dry as a bone. Left it to coolndown for a few hours then warmed it up and gave it a quick 2 mile sprint up n down the hill. Boost fully engaged on several occasions. Git back, coolant everywhere again, from the same place from the looks of it. 

Cleaned it up and left it a few days. got a new genuine sti 1.3 tank cap. Switched them over, Warmed it up, gave it some beans up n down the hill again. More coolant! :( 


It's not over heating at all. It seems it's fine if you drive steady with no boost, but once you get going the expansion tank vents out the top around where the tube goes in. It's always wetter on the right hand side. The aa guy topped the expansion tank up because it lost a fair bit on the A12. I've not done anything to the motor since I've had it and as far as I can tell it's all completely standard mechanically.

going to get a sniffer test for HG but anyone heard of this before and know the direction I need to be heading, please link a brother up!! 


:) thanks in advance 




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Could be a blockage or faulty thermostat but seeing as it only does it on boost you could well be right.

Sniffer test would give you a definite answer but unfortunately it does sound like typical early headgasket symptoms to me [emoji53] .

under boost the failing headgaskets allow the heads to lift which in turn pushes combustion gasses into the coolant , creating excess pressure in the cooling system.

Has it been mapped for the lower octane uk fuel ?

If it's not broke .....upgrade it 😊

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doin exact same as my wrx hatch was,ok driving slow with little rev or standing still,give it some revs and blows coolant out the overflow bottle,exhaust gas gettin in cooling system,does not show its over heading either my gauges said all was well but when you look't their was no coolant left in system only what was left in expansion tank,head gasket problem.

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Thanks for your input everyone!

I'm getting a sniff test done on Monday to rule out the HG. I have not be experiencing any performance issues and the engine seems perfectly balanced still and, as such, I cant see it being the HG. I'll know for sure Monday!

Speaking to a few people that know a lot more than me about this stuff, I am starting to convince myself there is a lose clip on/a leak in a pipe on the cooling system somewhere. It should have shown up when AA did the pressure test on the header tank but I seem to recall that he ran it at 15lbs and im told that is nowhere near enough to properly test the system on an engine like this! Anyone know what load the pressure test should be done at?

I am starting to look around for replacement pipes just in case. Can anyone make any recommendations on that front?

Im pretty gutted generally as it had been running a dream and was going to my first meet in Chelmsford this Saturday. I could take my ST but will just get funny looks no doubt :(

Cheers people.

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  • 3 weeks later...

For anyone interested, it transpired that the pressure test done by the AA was nowhere near high enough for the engine's capacity. A further test at much higher pressure revealed a leak in the top of the rad.

Getting a replacement rad was tricky to say the least. Eventually went with a Mishimoto as recommended by SVA imports, although it was an awful fit and Redline tuning in Basildon had their work cut out to get it on.


Anyway, she's now back on the road! :2guns:

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I have found all the mishimoto parts i have had so far have been poor.no big part.just 2 sandwich plates.threads were gone on 1 the other was ok.water temp housing.had to run tap in threads as paint in it .silicone hose for my hatchback was a b***h to fit.and a think their over priced as well.

Sent from my LG-D855 using Tapatalk

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