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Last Sunday my wrx over heated, I managed to spot the temp gauge and stopped imidiatediatley, I have had someone look at it and his conclusion was that due to the weather radiator caps can fail to release pressure, and since it has been running fine (driving very gingerly) however my local Subaru 'expert' seems sure it's a blown head gasket, dnt know who or wat to believe any advice would be much appreciated 

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Being a 2.5 i'd be leaning more towards the headgasket. best bet is get a sniff test done and see what the result is.

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HG quite likely, do gas analyser test on open cooling system and check head gasket seam for signs of oil residue/wetness
Leaks on these can start so small and only at certain engine temps and cylinder pressures they very hard fully pinpoint 100% due to minimal symptoms and test results .
Pressure test on cooling system, thermostat function and radiator flow/fin condition other things need ruling out .
 

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Would it still be driving ok though?? I haven't lost any coolant and drives fine,

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Is the 2.5 prone to hg problems? I assumed being a larger engine they would be a abit hardier?

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Plus I am getting a test done just unsure wether to carry on driving it 

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5 hours ago, bishaldinho92 said:

Is the 2.5 prone to hg problems? I assumed being a larger engine they would be a abit hardier?

 

2.5 has known issues with headgaskets and ringlands. They dont all go but a higher percentage than most engine types

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2.5 is indeed prone to HG issue in all versions .

If it not using water and not overheating then drive it but use some common sense if planning longer trips and realize this current heat wave could make things worse if out and have issues .

Most 2.5 odd heating issues always come back to HG given bit of time only had a couple that turned out more basic with thermostat and coolant sensor issues .

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Best bet is the sniff test that way you can rule out head gasket then do a pressure test that will expose any potential leaks  ,, is it air locking and pushing coolant into the overflow ? 

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early stage minimal HG issues that play up rarely at certain temps and cylinder stresses on the 2.5 many times test fine via gas probe sniff, liquid colour test and pressure test . If want 100% confirmation sometimes you got carefully wait and monitor and retest .

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comp tests can read fine too .
sometimes only way have available evidence for 100% diagnosis is give it little time .

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 Think I have cracked it i have a split hose that comes off just under the rad cap to a tee off to the expansion bottle, but can't find a name for 1, any ideas? Still got it booked in but not showing any common signs of head gasket ie goo on oil cap, white smoke or chocolate milk coloured oil on dipstick

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Smelling under the bonnet get ur nose and eyes up close the burning coolant will be pretty irritating to your eyes. That's what got me and helped me find mine. It was something as simple as a corroded hose clip, randomly on and off for a week I got random amounts of "vapour" once very prominent coming from under the bonnet. By the time my mechanic could look the hose clip completely failed so a £1 broken clip cost me £200(cost of towing, new coolant and labour) 

Even if small amount is leaking you will have some sort of sign water marks or wetness. 

Because of this I've order Mishitmoto radiator hoses, ancillaries and also intercooler along with tbolt clips 

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I drove it today after playing about today with it had steam coming from bonnet which like u said was irritating to my eyes, my friend and fellow Subaru owner had a look and we spotted the leak, just wondering what its correct name is to order a new one

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It's down to preference oh what you order, 

So hoses £300, the your probably looking £200 for labour and replacement coolant 

But priority would be to find the leaking hose and get clip replaced ASAP as if will go without warning 

Www.mishimoto.co.uk

 

Screenshot_20180715-000501.png

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Having sorted the hose I am still having overheating issues, had gasket test done nothing, had countless people look at it and can't seem to find an issue but it still every so often (not regulary) gets hot??!! Any ideas?

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In early stages of headgasket failure the sometimes only overheat when running at normal temps under boost , so don't always show up by a sniff test early on .

As when the coolant is running at normal temps (fan has cut in ,temp gauge in the middle) it's at its maximum pressure . This plus the extra cylinder pressure from air being forced in by the turbo (on boost) causes combustion gasses to seep past the falling headgasket,  pushing combustion gasses into the coolant and rising the coolant temps .

Subaru engines very rarely mix oil n water tbh .

Check the rad doesn't have a crack in the plastic near the overflow hose you replaced (common issue) 

Check top/ bottom rad and heater matrix flow and return hoses are getting hot when cars at normal running temp (fans cut in at idle) .as this might help rule out a sticky stat or airlock from the leaky hose .

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As stated few times headgasket tests means very little on these .

Thermostat wants checking for function and if decide replace it get oem or top quality as cheaper ones probably worse than old .

Want check radiator flow and cooling flow in general .

Want be sure coolant system got no leaks and holds pressure correctly .

My suspicion is early stage HG issue but could never diagnose it to a customer without more evidence .

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Had a very interesting conversation with an old boy down the pub on this subject tonight, was told check all spark plugs and make sure they are all the same colour ? If so it could be down to running too much boost , having had it on the rolling road the turbo is running maximum boost , he seems to think it will be pushing hot air back into the engine if overworked?

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The turbo wont be running it's absolute max boost.

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Only thing happen as turbo working near it's max is efficiency down thus charge temps higher with low density . If charge temps was ridiculously high you will have det and piston issues pretty fast .

Exactly when your overheat occur, always under heavy throttle and boost, cruising, in traffic ???
You best just being super thorough with hunting leaks, fitting new stat, testing flow and system pressure holding and if can't find fault give it little time until can .

Plug colours/deposits give you good idea on how it running and differing look indicates potential likely cylinder with issue/linked to issue . Will need a trained eye unless severe plug colouration/deposits .

3 things I see most for overheating is airlocks/small leaks and 'new' low quality thermostats and head gaskets, on the 2.5 roughly 8 out of 10 seem conclude as head gaskets .
 

 

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