andythejock01wrx

Hopefully someone more knowledgeable that myslelf will come along and answer that for us.

ALi-B

iTrader: (1)

The 2.5 is less tolerant to overheating.

If you look at the OP's problem, he had a hairline crack in the radiator. If that had been left unoticed (which is very easy to do), the cooling system may air lock. The first time you'll be aware of it happening is when the engine loses power and overheats - by which time its too late, it will have popped the head gasket.

Same goes for a botched coolant changed. May seem ok at first upon intial filling, but then during a drive it airlocks, overheats and screws up the HG.

Failure of HGs on tuned/modified/remapped engines is a different case, as the engine is put under stresses it wasn't orginally intended to do. As such, the HG and cylinder head bolt torques should be considered when upping the engine's output.

skinner

My headgaskets whet on my car hawkeye.When mine went i found little bits of paint in the expansion bottle from the headgaskets so look out for that all so i could hear warter rushing through the matrix.The problem with the 2.5 engine is there is a lot mre torque and the head botls are not able to cope you can uprate your head bolts to 14mm which will help.Another problem is the cylinder walls are thiner on the 2.5 and the move around slightley helping to the problem.It is not a mith about headgasket failure a lot have had problems as they have come out of warrenty.I used 1.1 cosworth head gaskets after the rebuild the flow was down on the radiator so that was replaced and had it mapped so far it has been ok hope this helps.

greatgonzo

iTrader: (1)

I hear water flowing through my heater matrix

ALi-B

iTrader: (1)

Worth checking the header tank and the radiator regularly with a cold engine (one at a time).

It should always pretty much full to the brim.

Same goes for the epanasion resvervoir by teh battery, whilst it will vary between max an min depending on engine temp, it should never need any constant topping up.

If in serious doubt, a cooling system pressure check can be done.

A "sniffer" test may not always work, as sometimes a minor gasket weep only occurs when the engine is under heavy load.

acstua

iTrader: (1)

It was a brand new rad fitted juggers

I got to cornwall without any trouble, which is good as i was stuck in loads of traffic on the way here :\
kept looking at the temp guage whilst say on the a303 by stonehenge for a good 40mins
but all good
averaged 27.5mpg :d

Did notice the engine was quite hot when i got to cornwall, as in when i opened the bonnet even the bonnet stay was very warm, but then i guess thats to be expected after the journey heh
also gave the car quite going over on the country roads without any funnys when i got here so all good

i did notice before i left some drips from a kinda T junction thing near the expansion tank, it had one rubber tube going off into the expansion
one of the other rubber tubes seemed a bit loose and where the coolant was coming from and dripping on to the rad top
but seemed dry after the journey so ignoring it heh

as above would be interseting to hear from anyone whos had a HG go more than once

pulse

what coolant mixture is recommended.

skinner

I would use the same coolant that is in the car mine had red toyota antifreeze in it which is really good most are 50percent warter 50 percent antifreez.

andythejock01wrx

Any thoughts as to what it is in the engine design that causes this Ali? There must be a common underlying cause if it's a known defect.

53

iTrader: (41)

If all the air is not expelled you can get this, not really and indication that your HG is doomed lol. Mine was changed, flushed inc matrix, bled properly and refilled with Motul coolant. Runs sweet ! no girgles 2.5's have a higher hit rate of HG complaint but not all dealers/services/drivers are born equal and improper serving, abuse, or blatant negligence are always going to accelerate the demise of extended service items in any engine

johnfelstead

The 2.5STi has less torque than the JDM 2.0STi.

No need for 14mm studs on a stock engine, the standard bolt size is fine.

Stock STi engines dont have liners, the cylinders are part of the castings.

If you want a reliable post headgasket change engine, then you need to ensure the heads and block are spotless and flat, that often means both the head and block need facing and then the rebuild is done with atention to detail, especially making sure during the block assembly the block faces dont get scratched, which is easy to do when you build the halves up on a bench.

ALi-B

iTrader: (1)

No real defect: The 2.5 is extremely similar in design to its 2.0 open deck sibling, its just a simple fact; Bigger bores are housed in the same size cylinder block, so its more stressed and less tolerant to extremes (such as overheating or running more BHP without block/gasket modification):

In the pics attached below: 2.5 on the left, 2.0 on the right (open deck)

Note the 2.5's thinner cylinder walls, noted by the notches cut out for the main bearing bolts, so less sealing area for the gasket. In addition, there is a slightly smaller water jacket capacity.

Whilst both the 2.0 and 2.5 open deck designs have strenthening metal to hold the bores to the outer block the bores can still move by a very small amount which can cause a wear issue on the gasket. Both engines can suffer this, but obviously the one with the thinner cylinder wall thickness area will be less tolerant to overheating and extreme stresses.

In the case of the engine in the left pic, it has had dowl pins inserted to try and reinforce the cylinders, normally these aren't present, its mostly open deck design. Other builders decide to close the cylinder deck by welding in metal to join the bores to the outer casing of the engine block. There are pros and cons with this...Pros: better block rigidity. Cons: it reduces coolant capacity, impedes coolant flow and can cause thermal expansion/stress issues (which could crack the cylinder walls).

Edited to add; Not performing coolant changes as per the service shedule or using too weak anti-freeze allowing corrosion doesn't help one jot (with either engine).

skinner

I would advise up rated head bolts even if ther not 14mm you can get arp or cosworth that directley replace the standard ones what is the point in doing a job twice.If there is no problem with them why do they keep failing.The 2.0l jdm has thicker cylinder walls than the 2.5 sti .

andythejock01wrx

Unless I'm being my usual "dolly dimple" IT illiterate self there's only one pic (plus a larger version of the same)?

Anyway, thanks Ali, that's very helpful.

I'm slowly building a picture. To be honest I'm still likely to get an 06 or 07 2.5 STi, but at least I'll be aware of the issues. Of course I've never seen any stat's to suggest how common the problem is ie is it 10% of cars or 30%?

Andy