Just an idea ... but why not.

In spite of new PCV valve is it possible that crankcase pressure is not
being relieved as designed?

Such pressure could cause that drip to increase at highway engine
speeds but you would only notice a slow leak when it is parked at idle.
Is there a way to check the crankcase pressure - say by holding a film
of plastic or a light disk over the oil filler opening awhilst revving
the motor a bit?

Date: 3 Jun 2005 10:28:27 -0700
Leo_Lennox@Hotmail.com wrote:

Well, I haven't seen any frothy oil under the filler cap.  I'll give
the oily cardboard a try.  Thanks.

Well, I tested for overpressurization of the crankcase, as suggested
by Gord Beaman & Leo Lennox.  Comments below.

Leo_Lennox@Hotmail.com wrote:

I tried a couple of other things prior to sampling the pressure at the
oil filler cap.  I checked the all spark plugs against pictures in the
Haynes manual, and even brought it into the parts guy in an automotive
store.  It was fine, no residue, blistering, or flaking, or structural
degradation.  After reading what there was to it, I was worried about
crossthreading, but that didn't happen.

I then put the front end on a pair of jackstands and revved the engine
for just over 2 minutes.  I looked at the seepage coming from the
rear main seals (or the transmission, not sure which), and it didn't
seem any worse than before.  In fact, it seemed less.  So revving
the engine for 2 minutes doesn't contribute noticably to the oil loss,
at least not when it's free from loading.

I was all set to "test" the sump pressure by pressing an oil-drenched
cardboard against the oil filler opening.  Then I realized that I had
only tranmission fluid.  I used the filler cap to test the
overpressurization hypothesis.  Basically, before the filler cap is
fully screwed down, there is some vertical play.  Pressure from the
head should push it up a smidgen.  But it doesn't.  As I screw the cap
down tight, there is no hissing of gas to indicate a high pressure
inside.

To further test the PCV (beyond shaking the valve to listen for a rattle),
I took out the valve and hose (as a single unit) and blue from each end.
Air blew through readily in the forward direction, less readily in the
reverse direction.  (I read about this in Haynes, which suggested not
putting one's mouth in contact with the PVC parts; rather, use a clean
rubber hose to direct one's breath into the parts).

To test the PCV beyond any reasonable doubt, I replaced the parts and
used my hand to pinch the hose, with the engine idling.  The engine
did not sputter as expected, but I heard a distinct clicking sound,
which I assume was the valve.  Every time I pinched the hose, it
clicked.  I have no idea whether that behaviour makes sense, but at
least I know it's responsive.

As a final test of the PCV, I yanked it out and idled the engine.  The
engine cyclically revved up and down, in about 3/4-second cycles.  I
assume that is the computer algorithm going around in circles, since
it is calibrated for an engine with PCV in-place.  But at least I know
the PCV forms a closed system, since the cyclic revving stopped as
soon as I put the valve/hose back in.  It did not seem to matter
whether I pulled out the valve end or the intake manifold end in this
test.

I think I can safely discount the hypothesis that overpressurization of
the crankcase amplifies the seepage at the rear main seals when the
car is running.

The only remaining possibility is that the oil is entering the
combustion chamber, burning, and being expelled with the exhaust.  As
I mentioned, there is lack of any indication of bad rings -- engine
does well on compression & leak-down test, exhaust is clear, analysis
of exhaust allegedly shows normal composition, and no oil on spark
plugs.  Furthermore, there is no indication of head gasket problems --
no loss of coolant, no white gunk on spark plugs, no rusting of spark
plug threads, no cross-contamination of oil/coolant,

I visited the local master guru in town, the one that suggested
reporting back to him after a 2-hour drive.  He said that in order for
oil to show up on the spark plugs, I would need to be burning around
1L/300km.  Yeesh.  He also said that in order for exhaust to be
unclear, the amount of oil being burned would need to be in the same
ball park as the amount of fuel.  So the absence of these 2 signs
doesn't detract from the hypothesis that oil is burning in the
combustion, though neither does it resolve the fact that compression
and leak-down tests are good.  Say the rings are good; if the oil is
getting into the combustion chamber through an isolated bad spot in
the head gasket, one would expect this to show up on
compression/leak-down tests.

Another local Toyota technician suggested using oil dye.  This kind of
dye glows when illuminated with UV, so any leakages that are hidden
from the naked eye can be found.  Before putting this dye into the
oil, the engine should be shampooed and air dried, which should take
about half an hour, I'm told.  After that, it's a matter of running it
for a week and waiting for the dye to work its way out at the leakage
points.  This is definitely worth doing to eliminate the possibility
of barking up the wrong tree and changing the engine for nothing.

I am considering having an emissions test done to corroborate the fact
that the oil is not showing up in an analysis of the exhaust.

Anyway, the costs for these individually are small, but I've done
quite a bit of this and it is just adding up.  I'm wondering whether
it's wise to just throw in the towel and let the engine be changed.
I'm just concerned that it will be crappier engine, with a worse
result in compression/leak-down tests (definitely the valve seals
will be worse, as the current ones are new), and the problem of
loss oil and caustic fumes might not even be solved.