I've been looking at used Subarus, most of the older 90s models have the 2.5 engines.  Is there any way to minimize the risk of the head gaskets going bad on these?  Lower speeds, never over 65, no towing, no lugging up too steep inclines, ideal fluids in radiator, oil, etc.?

The easiest way, don't buy one or expect it to blow and swap a 2.2l when it does

You could try a drain and refill of the coolant with the latest Subaru coolant and add the conditioner.  It wont fix anything but it might delay the failure.

What's the percentage chance of failure?  100% 50% 35%?  Is there a way to know if it has already been done?  

I know I'm definitely out of the norm. But my first car, 97' outback with that engine. And it had head gaskets replaced at 200k for maintenance...they weren't even leaking nor was the car over heating... So that might be the 1 in a million car but, *shrug* also, that car had 300k on it when I sold it. 

 

Edit: maybe it was a 98' or 99' I don't know... All I know is it had that engine that is "prone" to head gasket failure.

Edited March 19, 201610 yr by golucky66

I've heard it's close to 100% failure of the EJ25D engine in '96- '99 Outbacks, usually give or take at around 150K miles. The coolnat conditioner was actually deisgnated for the 2000+ EJ251 engines in oreder to dslow down the development of external coolant leaks.

The easiest way, don't buy one or expect it to blow and swap a 2.2l when it does.

 

Totally agree these (EJ25D) were notorious for internal headgasket leaks, overheating then possible internal component damage.

 

Even if H/Gs have been replaced  ie before purchasing car there is a element of risk that this has happened as well.

 

You would be far better looking at the later 2000-2004 (EJ251) these still had H/G issues but were predominantly external leaks (not as bad)

 

The best  way to minimise / delay headgasket issues is to change fluids regularly.   ie flush / replace coolant in cooling system every two

 

years  and changing engine oil /filter every 3000 miles and the addition of Subaru coolant conditioner as previously mentioned

 

The problem with ALL Subarus is because of the flat configuration of the boxer engine -  makes it more vulnerable 

 

to contaminated  oil / coolant   staying in contact with seals  / gaskets - which can eat these away over time;

 

compared to a vertically configured engine where these contaminated fluids can partially drain away from / gaskets seals etc. 

 

Am posting 2 links which which discuss these issues fully:

 

https://allwheeldriveauto.com/subaru-head-gasket-problems-explained/

 

https://allwheeldriveauto.com/subaru-head-gaskets-problems-explained-part-ii/

Edited March 19, 201610 yr by subnz

I would think that various extraordinary measures could be taken to decrease the stress on the running engine; synthetic engine oils, synthetic antifreezes with exceptional properties.  Babying the car, not running it at high speeds, etc..  

Not really. The thermostat is going to regulate the engine temp. The cooling system can cool the engine a lot more if a different thermostat was there.. Your thinking along the lines of air cooled where the cooling is variable based on load and ambient temp

Do you have a link to the best thermostat for the 2.5?

I would think that various extraordinary measures could be taken to decrease the stress on the running engine; synthetic engine oils, synthetic antifreezes with exceptional properties.  Babying the car, not running it at high speeds, etc..  

 

Fancy oils   plus additives etc not necessary   the use of   recommended reasonable quality multigrade oil and coolant additives is all thats necessary.

 

The most important issue with them is to change fluids regularly as I previously suggested.

 

Subaru H4 engines work / perform  best  by driving them normally (ie not babying it nor thrashing it)  ie by keeping the engine spinning between

 

2500 -3500 rpm for best power torque economy reducing stress on engine under load.

 

The best thermostat is a genuine Subaru one as other aftermarket ones can cause problems

Edited March 19, 201610 yr by subnz

Stant Xactstat 48457 is exactly the same as  the oem unit and cheaper.

 

O.

find one with blown engine, build an engine for it with turbo (mls) gaskets. Be prepared for rod knock if you don't rebuild to the bottom end. Might get lucky and overheat was minimal.

The engine on the 97 Outback is running cool, what an improvement over the last one.

My experience is 100% chance of it happening, it's just a matter of when; 60,000. miles, 150,000. 200,00?  Spin the wheel take your chances.  I put a 2.2 in my 97 it was fine until a hose broke on the freeway and I didn't notice for too long of a time and cooked it. 

I've been wondering if the HG failure rate on the DOHC 2.5L isn't a result from using too small diameter head bolts? If the 2.2L doesn't have the HG issues, what's truly different other than the head being lighter and only running one cam and sprocket? 

 

I've wondered if you drilled out and tapped the heads/block, and went with a beefier ARP head bolt (non stretch) and maybe added 25-45 more ft/lbs while also running a top-grade HG, if it wouldn't eliminate the issue altogether. Having the extra weight and stresses from 2 cams on the smaller head bolts might be the reason failures are so predominate with that engine, especially if the bolts aren't keeping the head firmly in place.

No because the Turbo engines are essentially the same head bolt/ cam arrangement as the EJ25D.. The bolts are different, but not in diamater given the threads on all Subaru blocks are the same.

the only theory I have read about it, was that the 2.5 open-deck jugs just 'move around' too much for th 'old style' HGs.