Thought this is interesting and couldn't find in archive.

 

http://www.maddyhome.com/canardpages/pages/alwick/engine.html

 

 

One thing I noticed is that the author did many 'injected cooling system overheating' tests on EJ25 by getting small amount of air trapped in the cooling system. And succeeded to warp the head after few tries.

 

And addition of a small air vent on top of block pretty much fixed everything and made the engine bulletproof to overheating (and head gasket failure, warped head, etc.).

 

I was wondering whether most head gasket failures in EJ25 engines were due to similar reason. ie. Small amount of air got trapped after coolant change, caused bad heat transfer under heavy load, engine got overheat and head gasket blew...

 

OK. I was daydreaming but I hope someone more knowledgible can comment on this thought.

Sound eminently sensible to me... its the sort of test an aviatione ngineer would dream up, just can't afford not to have every precaution taken for longevity. They never just throw these things into an aircraft, always re-engineer them, downrate them useually and pay particular attention to the actual installation - as with say, Kubota static engines, they won't sell then to anybody without exhaustive installation/reliability trials... reputation!

 

With the new Gen Subie's proclivity to cooling system bleeding difficulties, does this expalin the 2.5's growing reputation for head gasket problems?

I think it may explain at least some of the failures. I worked on a buick 3800 about a year ago that had a nice bleeder on the top of the engine for bleeding the cooling system. Made it much easier and more idiot (me) proof.

He actually said:

"Head warp caused by customers changing their coolant is now the number one warranty item with this engine. All caused by an engine block that was not plumbed to dynamically remove air from the high point. Subaru has since changed their cooling system design."

 

Is the 2.5 gen II SOHV the one with improved plumbing?

This site is fun.

 

Flying Subies

 

Subarus are everywhere!

Can anyone detail exactly where that vent is best placed, or whether the Phase II's have it already? Not having either, but looking at 2.5 II I'd like to have that information..