I noticed on my last oil change that my 250k mile 08 corolla is consuming oil (no noticeable exhaust smoke). My best estimation seems to be about 1 quart every 2500 miles. I have no big oil leaks currently so my oil loss is not from that. The PCV valve still rattles freely and I cleaned it with some spray cleaner (nothing serious came out of it) so I don't think it needs replacing. I tried a flush in my last change thinking it could free up any potentially stuck piston rings or something. This didn't help the issue by any significant amount (within margin of error).
What could the issue be? What can be done to mitigate this consumption issue shy of rebuilding the engine.
What could the issue be?
It's a worn out engine - usually the piston rings get stuck, sometimes the cylinder becomes oval in shape.
At 250k miles, It has lived a long life - and it'll probably last a lot more if you just keep adding more oil.
If I remember correctly, Toyota says up to 1 quart per 1,000 miles is permissible on cars with the ZZ engine,
and I've seen those cars burn much more and still go down the road good enough (as the ZZ engine had a tendency to consume much more oil in previous years of production - Toyota made some design changes to mitigate it and if it has only began to burn oil at 250k, then obviously the design changes worked)
The next model year had the early version of the ZR engine and those burned oil like mad even at 1/5 of your millage.
Was it an E120/130 model?
and was it an auto - if auto, how many transmissions has it gone through?
or is it on it's original transmission?
what other parts did it need getting to 250k?
E120/E130
E140/E150
It is the older style one from your pictures (E120/E130). It is automatic. Original drive train still. Definitely can feel the age sometimes. Haven't replaced anything more major than an ignition coil + consumables.
So is there nothing I can do to alleviate the burning? Is it the PCV valve, how would I know? Is there some better flush type product that could help? Or is there some oil additive that works?
Not really, you could replace / rebuild the engine.
The PCV valve elevates pressure inside of the crankcase. Excessive crankcase pressure will cause oil to get into the combustion chamber and burn.
Corollas are naturally aspirated and as such during normal operation there’s very little blow by that’d cause crankcase pressure to rise, and very little oil vapors to clog up the valve - so on an old Corolla seeing a PCV valve cause oil consumption is almost unheard of…
But I’d replace it anyway, usually it’s a few bucks for the part.
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As far as oil adaptive sans flushes, it’s all snake oil from my experience.
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There’s an overnight soaking procedure, as used by Kia as a last resort before engine replacement - but results are often very limited but sometimes it does slightly reduce consumption (the procedure consists of pouring special cleaning liquid into the spark plug holes, applying pneumatic pressure, and then letting it soak for at least 8 hours, replacing the oil and hoping for the best)
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Usually if the cylinders are deformed or the oil rings are stuck - not much you can do without taking out the engine except just replacing the oil more frequently and adding oil when needed.
As a practical matter, a quart every 2500 miles is really not that bad. If you had a new car most manufacturers consider up to a quart every 1000 miles to be "normal" for warranty purposes. If it's otherwise running OK just top up the oil as needed.
What could the issue be?
I would say it has mostly to do with having a quarter-million miles on it.
If it made it this far with just a little oil consumption then I'd say the engine has done pretty well.
So is there nothing I can do to alleviate the burning?
practically, no
Is it the PCV valve, how would I know?
they're usually pretty inexpensive (although lately part prices are nuts. my oil filters have gone up 150%!)
If you've never replaced it just drop one in
Is there some better flush type product that could help?
Scotty swears by this ATS stuff.
https://carkiller.com/scottykilmer/qa/ats-505-cro-oil-treatment-result-review-2/
Or is there some oil additive that works?
you'll spend more on the additive than the oil. It's pointless.
Not a big deal, my 98 corolla at 100k miles was burning a quart every 2k miles, and that wasn't that bad.
My 05 Matrix at 200k miles goes through a quart about every 3k, which I am totally fine with. I just get a quart of cheaper oil to top up on, like supertech full synthetic, and keep it in the car.
They may burn a bit of oil, but they will do it for a very, very long time.
