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Discussion Starter · #1 ·
My wife has a 2012 2.5L Outback with about 115k miles. It has been maintained according to the book schedule for it's entire life. Last week the engine all of a sudden shuttered then quit and wouldn't restart. Our mechanic (whom I trust) was hoping it was just a sensor since one of them was full of carbon but today he ran a compression test and found that the number 4 cylinder is shot and has no compression. He doesn't think it is the head gasket.

This seems like really low miles for engine failure when maintained and not agressively driven.

A. Would nicely pleading with Subaru for goodwill get me anywhere?
B. Is it worth spending $1500-3000 all in to put a used or rebuilt engine?
C. He didn't recommend repairing the engine based on the cost to repair vs issues mixing new parts in the used engine.
D. Is his diagnosis wrong?
 

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2010 2.5 CVT Limited
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Ask your mechanic if he can boroscope the cylinder to see what's going on inside. If it is limited to a valve failure, that is very repairable. If it is a major failure like a piston or connecting rod, then an engine replacement is a better option.
 

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Discussion Starter · #3 ·
Ask your mechanic if he can boroscope the cylinder to see what's going on inside. If it is limited to a valve failure, that is very repairable. If it is a major failure like a piston or connecting rod, then an engine replacement is a better option.
Will do. I was just on the phone with my dad (retired mechanic) and his initial feeling from 200 miles away was the timing belt slipping off or something like that. It was just replaced at 105k. Does that sound reasonable? He is just surprised something catastrophic happening when it has been maintained to the book.
 

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The #4 cylinder on subaru engines is known for burning the exhaust valve due to lean running. (something about the shape of the intake plenum adding slightly more air on each intake stroke)

Usually, this never escalates to a failure... but there are always circomstances which can lead to failure. (vacuum leak in intake manifold, weak injector on #4....etc)
 

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Outback 2011 3.6R Premium
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There have been reports of a “dropped” exhaust valve guide in some motors which does not allow the valve to seal, resulting in no compression in that cylinder.

At this stage I would be getting further diagnosis of what the actual problem is rather than deciding to replace the whole engine.

Seagrass
 
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I think if the timing belt slipped enough to mess with the compression stroke in one cylinder, it would affect all the cylinders. Also, since it is an interference engine, it would be a small (if even possible) window of mislignment that affects compression and does not crash the valves into the pistons.
 

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Discussion Starter · #7 ·
Thanks for all the help. I am going to take a trip over to the garage tomorrow and talk things through with my mechanic and figure where to go next.
 

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You can easily check for a dropped valve guide by unbolting the exhaust from the engine and looking at the valves, a dropped valve guide is fairly easy to see.

A timing belt can jump a couple of teeth without causing valve damage (but the engine will not run properly). If you had the timing belt changed recently AND all of the idler pulleys and tensioner were also replaced then it would be unusual for the timing belt to jump teeth.

Seagrass
 

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Discussion Starter · #10 ·
You can easily check for a dropped valve guide by unbolting the exhaust from the engine and looking at the valves, a dropped valve guide is fairly easy to see.

A timing belt can jump a couple of teeth without causing valve damage (but the engine will not run properly). If you had the timing belt changed recently AND all of the idler pulleys and tensioner were also replaced then it would be unusual for the timing belt to jump teeth.

Seagrass
I do know everything was replaced when the timing belt was. I will ask the mechanic about the valve guides. The frustrating thing is that it appears the valve guide issue shows up in poorly maintained engines but we followed the schedule in the manual closely and my wife isn't a crazy driver.
 

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poor quality fuel will also cause valve guide issues. last time you ran injector cleaner through it?
 
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