Strange oil consumption issue with '04 Corolla

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My Corolla now has 345K miles. From around 150K miles to around 300K miles, it used 1 qt between oil changes (every 6K miles), which I considered to be normal considering its mileage. At around 300K consumption jumped considerably. It now goes through a qt every 700 miles. I changed the plugs about 20K miles ago and they had about 120K miles on them. They looked normal (they had a light tan powdery haze to them) and the electrodes were still in good shape. I expected them to show signs of oil fouling, but they didn't. I also changed my PCV valve, which did nothing to slow consumption. The car doesn't smoke when started after being parked over night, nor do I see any smoke coming out of the tailpipe when I'm driving. I had car headlights behind me at night which really shows a smoking engine, but mine shows nothing. Question is, where is this oil going? Could it be going out the tailpipe without burning it? It could also be going out through another part of the PCV system, but it seems like I'd be able to see it somewhere. It also doesn't leak. The engine runs fine and I'm just going to keep driving it until something major goes, but I can't figure out where all of this oil is going.
 
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That car/engine owes you nothing at this point & time in its life. Consider doing a piston soak or moving up to a HM oil or up in viscosity also?
 
Without looking into things like the pcv valve, oil leaks, valve seals, doing a compression test, and a leak down test it's hard to tell what is going on. With that kind of miles on the clock sooner or later something is going to let go.
 
When you changed the PCV valve, did you use an OE one or an aftermarket one?
Having said that, at 345K miles, one quart every 700 miles isn't horrible.
 
Originally Posted By: MarkM66
Converter is burning it smokeless.


This.

It takes a lot of oil burning to show smoke with cat converters. My GF's Prius burned a quart every 800 miles and no smoke was visible.

With 345k, my guess is the valve seals and/or piston rings are getting worn.
 
98-02 Corolla engines were ravenous oil burners. Clogged piston oil return holes when cheapo oil was used. They changed the pistons and its not much of an issue anymore. But.. its an aluminum Toyota engine with a thin skin. So it still has the potential to fry cheap oil in those holes.
 
Originally Posted By: turtlevette
What are you expecting?



To find out where the oil is going.
 
Originally Posted By: ZZman
Hmmm. No idea. But I would be happy the car is still running.


I am.
 
Originally Posted By: jeepman3071
Any leaks? Valve seals could be worn also.


No leaks, and if the valve seals were bad, I'd see smoke when I first start it up...
 
Originally Posted By: PimTac
Assuming you have checked for any leaks like the rear main? What oil are you running?


Supertech
 
Originally Posted By: zzyzzx
When you changed the PCV valve, did you use an OE one or an aftermarket one?
Having said that, at 345K miles, one quart every 700 miles isn't horrible.


Aftermarket
 
Originally Posted By: grampi
Originally Posted By: turtlevette
What are you expecting?



To find out where the oil is going.


Its being burned. The plugs are hot enough to burn off the residue.
 
Sounds like a candidate for a diesel flush. Drain the oil,replace with same amount of diesel. Start and idle for 15 minutes. Repeat at the next OCI. Cut the oil filters open looking for hard carbon bits.
 
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