I was hoping I could get some help/advice regarding a Subaru Outback 2.5 SOHC (EJ251) 2000. N/A

It is a donor engine that needed the head gaskets replacing. Before I put this engine (which has done approx. 128K miles) I replaced the head gaskets, had the heads skimmed, checked, cleaned, valve re-seated and new valve stem seals fitted by a local very good engine company. I also replace the cambelt, oil/water pump, pulley, plugs, leads ect ect while it was out.

The engine is running great however it is using SOO much oil, it has used about 3litres (over 3 quarts of oil) in a little over 500miles. There are ZERO external oil leaks and it is dry as a bone on the external. Yes it does smoke (mainly White’ish) on start-up but not excessive and even under full throttle it not particularly noticeable. It does smell very rich.
It pulls well and no loss of power – I have checked the compression before however I can remember what the number were but they were all well within 5% of each other which I believe is important part of a compression test.
I have tried using thicker oil (as far up as 15/50- I live in the UK) and have also checked the PCV valve and replaced twice to be sure with OEM ones.

So any help/guidance would be great – I am thinking it has to be either worn compression or oil control rings or badly installed/incorrect valve guide seals but I am hoping somebody could help me find the issue.

 

Wow that's a lot of oil.
Can you get someone to drive behind you or even better get someone to drive your car and you drive behind it?
should be able to see any oil smoke from exhaust.

 

When you replaced the h/gaskets did you remove the carbon on top of the pistons & from the top of the bores ?


It will not be your valve stem seals causing that amount of oil use, even if you never fitted any.

 

Only on the surface of the pistons. I didnt take the pistons out and clean the rings/skirts/ring lands ect.

 

That's your problem, you have taken off the top carbon, which helps hold the carbon on the top ring lands on to the piston, that comes off & the carbon build up on the ring pack is also effected, all the carbon sealing your worn ring grooves lets your oil pass.


If your going to do that your best to leave at least 10 to 15mm from the edge.

 

OK, that kinda makes sense - thank you, so the only option is to replace the piston/oil control rings??

 

If your keeping the car the best way would be new pistons & hone the bores to suit, the 2.5 bores to tend to go oval & taper, even the non turbo ones.

 

Thanks again m8, really appreciate your help/advice.

So you mean new pistons as well as the rings. I am assuming standard OEM size (99.5 bore I think ) and re-hone the bores?

Will I need to split the block to hone or is there away to hone the full length of the cylinder and keep the crap out without splitting the block?

 

Yes, new piston assembly's, aftermarket std cast pistons for the 2.5 are not expensive, but you will need to split the casings, otherwise with the conrod in the bore you cannot hone to the bottom, or keep it clean from contamination.


You could clean up your old pistons, fit new rings & de glaze the bores, but you might end up in the same place you are now.

 

Excellent - last questions I promise. I am sure you have work to do

Ok I will look at getting new pistons and rings and look to hone before installing.

Working on the assumption that the bore oval/taper is within tolerance I believe there are two different sizes of rings that were use din these engines. I think Subaru have them classified into two grades, “A” and “B”


A: 99.505 — 99.515 mm (3.9175 — 3.9179 in)
B: 99.495 — 99.505 mm (3.9171 — 3.9175 in)

Is there anyway of finding out which one mine has?

 

It should have it on the top of the block, on the centre join line there is a machined flat surface with it stamped on, it is also on the pistons.