Strange Oil Leak: Fast then Slow

[ericdude]

1989 Toyota corolla has strange oil leak.

Originally, I thought it was a front seal leak because I saw the
oil dripping from right below the main crank area of the timing
cover, but:

* Oil leaks only when engine is running or has been run
* Oil leaks rapidly when dipstick is filled to the FULL mark,
then much more slowly after oil reaches about 1/2 mark between
FULL and LOW.

This is confusing to me because I would assume that when the
engine is running and the oil pump is running, it doesn't matter
how much above the LOW level the oil is--the pressure should be
the same. So why would the leak rate depend on the level? A
Front Seal leak shouldn't care about the level.

If it were leaking because the pan gasket was below the oil
level at the FULL mark, then it should leak all the time, even
with the engine not running.

Only theory I have right now is of perhaps a temperature
dependent pan gasket leak. As temperature goes up from running
the engine, viscosity of oil drops (it gets thinner) so it can
leak through the gasket.

 

[c3po]

A couple of thoughts, when was the last time the PCV Valve was changed, if it has not been changed in a while do this 1st.

I would also look at the PCV hose and make sure it is clear.

How many miles are on the engine.

What is your oil change interval.

What type of oil and oil filter do you use.

Also can you post any pictures.

 

[jldcol]

You may have enough stuff in bottom of pan to raise the top of the oil level above what it should be. As engine runs oil is thinner as well as being thrown/sloshed/misted around the leaking area. If leakage is much lower at the 1/2 down level than the 1/2 up level, just leave it there, the proper level is 1/2 way between add and min marks.

 

[c3po]

Are we saying he has some junk in there that needs to be cleaned out of this engine.

 

[jldcol]

Possible component of trouble. Also I think a front seal leak will generally get on belts/pulleys/whole front of engine. Is any of this occuring? Maybe a leak from higher up.

 

[Camu Mahubah]

It's the gasket that seals the timing chain cover. I have seen this exact same thang on a Toyota pick-up.

 

[ericdude]

Originally Posted By: c3po
A couple of thoughts, when was the last time the PCV Valve was changed, if it has not been changed in a while do this 1st.


Is the PCV part of the EGR subsystem? I have been getting a
engine code related to EGR failure for a while. How would a
PCV failure cause an oil leak?

The vehicle has 175K and only recently started getting regular
oil changes. (I did one about 3K ago but before that it was
probably 1.5 yr on the same oil.) Valvoline High Mileage 10w30
purulator filter. (Was leaking much worse before the high
mileage oil.)

Originally Posted By: jldcol
You may have enough stuff in bottom of pan to raise the top of the oil level above what it should be.

Ok, I'm a bit confused. Since the geometry of the dipstick
doesn't change, how would gunk in the bottom affect the FULL
line? It would just mean that less real oil is present at FULL.

Originally Posted By: jldcol
Possible component of trouble. Also I think a front seal leak will generally get on belts/pulleys/whole front of engine. Is any of this occuring? Maybe a leak from higher up.


Yes, when the leak rate is high (oil at FULL level), you can
see residue on the crank belts. The timing belt is not visible,
of course, so it can't be inspected.

Originally Posted By: Camu Mahubah
It's the gasket that seals the timing chain cover. I have seen this exact same thang on a Toyota pick-up.


Well on the 4AF engine (corolla), the timing belt cover is just
a dust cover. There shouldn't be any oil on the timing belt
(provided the main seal isn't leaking), so a faulty timing
cover gasket wouldn't cause an oil leak. The pickups use
a different engine (22RE?) which, if I take you at your word,
use an internally lubricated timing chain. There is an inner
oil pump gasket on the 4AF, but I don't hear of that failing
as much as the front seal.

Thanks to all that responded...

 

[JonnyHotcakes]

Bump for you, my friends. I'm experiencing a similar issue.

 

[jldcol]

If you have 4inches of pan depth and then have 1inch of build up the oil will splash easier in the shallower oil depth, and I think the build up will highest at ends of pan, the center gets some removal with oil changes.

 

[mechtech2]

You leak is obviously not from a pressurized source. It's from splash.
So a front seal could still very likely be the culprit.