Plugged EGR system leads to burned oil rings over time -- cautionary

[Hank]

Cautionary, because this information wasn't something I found when I
need to know it last March before I bought a used 1988 GL Subaru wagon.

The EGR system had a problem the previous owner's mechanic hadn't
solved -- kept getting the engine check light code for EGR valve
solenoid.

Solenoid was good, valve was good.

The previous shade-tree mechanic had crimped the tubing that takes gas
from the exhaust side of the combustion through the valve back to the
intake side (it's there to reduce the oxygen content in the combustion
gases once the engine heats up).

We fixed the tubing. Didn't help. The first mechanic I found cleaned
out the port in the engine between the EGR valve and the intake side,
which he found completely plugged with carbon. That didn't help.

The second mechanic found that, duh, there are two ports -- the other
one, out from the exhaust side to the EGR, was stilll completely packed
solid with carbon.

Fixed that.

Engine started losing a lot of oil at that point. Did the head
gaskets. Didn't help, made it worse. Oil rings shot, although it
hadn't been doing too bad for oil loss before I bought it.

What happened is:

-- Plugged or blocked EGR system, check engine light comes on
-- (Code 34 in the old GL series)
--- Increased gas pressure on exhaust side of engine
-- Too much oxygen in combustion mix when engine is at normal temp.
-- Mechanic fails to figure it out before the ports plug up
-- Mechanic disables the EGR system by crimping or plugging it.
-- Engine oil rings start to burn and eventually sieze up in the rings.
-- Oil use starts to become a problem.
-- Mechanics think it's the gaskets and replace them, planing the heads.
-- Getting the heads planed down slightly increases compression slightly
-- Blowby of oil past rings becomes fatally bad.

I learned this from the engine rebuilders today. The guy who owned my
car before me trusted his mechanic who told him, oh, ignore that light,
it doesn't matter -- and the mechanic had crimpled his EGR tubing and
disabled the solenoid, after being unable to fix a persistent Check
Engine light with an EGR Valve Solenoid code

The rebuilders told me that recently they have seen several Subaru
engines come back to them on which some bright mechanic and had given
up after replacing the EGR valve solenoid a few times, and either
disabled the system or left it clogged up without understanding that
the ports had already clogged with carbon, while the EGR system wasn't
working.

So they crimped the EGR tubing or put a plate over one of the EGR
ports, thinking that it made no difference in how the engine ran.

And, over a year or two or three, according to the engine rebuilders,
the excess pressure and bad combustion gas ratio kills the engine by
damaging the oil rings.

(They give a 3-year warranty, so they see'em come back when something
fails, and figure out why.)

 

[Rick Courtright]

Cautionary, because this information wasn't something I found when I
need to know it last March before I bought a used 1988 GL Subaru wagon.

Hi,

Interesting, especially since your symptoms are quite like those my
engine exhibited before giving up the ghost. It's a '90, so essentially
identical to yours. I haven't torn it down yet, but did run a
compression check before putting it to rest for when I have more time to
play with it. Right side (No 1 & 3 cyl) were damaged, loss of about 50
psi on No. 1, TOTAL loss on No. 3 (ZERO compression.) The way the
compression tester reacted (didn't even bounce the needle), I guessed
broken compression rings or even a hole in a piston on No. 3.

Did you lose one side or both on yours?

Rick

 

[Hank]

Did you lose one side or both on yours?

Neither; just oil burning, half a quart in 300 miles at the end. My
engine goes back to the rebuilder and they promised to let me know what
it looks like inside, to be certain where the oil was going. This was
their best guess from knowing the EGR problem history.

Before the head gaskets were replaced, compression was ok (per the
mechanics; I don't have a way to work on my own vehicle). Oil loss got
worse after that.

I've been told and read that oil rings failing to scrap oil off the
inside of the cylinder so it goes into the combustion chamber actually
increases measured compression.

Searching the net I see EGR warnings that unburned carbon builds up in
the passages and has to be cleaned out every 20-30k miles (worse with
newer multiple port systems because one can clog first, making damage
uneven; my old single port fuel injection 1988 GL put all the EGR gas
into the manifold, I guess, downstream of the fuel/air intake but
upstream of the division into the four cylinders).

Also lots of warnings that unburned carbon damages oil rings.

I've gotten replies at www.usmb.net's forum for older Subarus from a
knowledgeable engine builder, a youngster who builds racing and high
performance engines, basically saying there's not much concern; my
guess is he's aiming for a different kind of engine behavior and is
willing to trade off higher temperatures and more frequent engine
rebuilds, to block the EGR system on the engines he builds. But I
can't say for sure.

As always my guideline is: "to get good information on the Internet,
post what you think you know and await correction"

 

[S]

Hi Hank, All!

So they crimped the EGR tubing or put a plate over one of the EGR
ports, thinking that it made no difference in how the engine ran.

And, over a year or two or three, according to the engine rebuilders,
the excess pressure and bad combustion gas ratio kills the engine by
damaging the oil rings.

Maybe. But . . .

FWIW, JDM engines I've installed (Toyota 4AG specifically) don't have
EGR hardware. The first one I did, I went to the trouble of swapping
_both_ manifolds to get the EGR working. The second was in my personal
car; I didn't even bother. Passes Colorado emissions just fine, and
has been trouble free for the last 3 years (~20K miles) . . . this on
a regularly driven MR2 that also doubles as an autocross and track car
on the weekends.

Lotsa things can potentially cause premature oil control ring failure,
but the EGR circuit seems an unlikely culprit. In fact, I'd have
reasoned that:

Engine oil control rings begin to lose seal, allowing oil into
combustion chamber. Oil in combustion chamber generates carbon (smoke)
in exhaust gas. Carbon passes into intake via EGR, and thence into
combustion chamber. Carbon in combustion chamber contributes to
fouling of rings/loss of seal/additional oil in combustion chamber . .
..

I would suggest that if an engine is producing enough carbon to plug
the EGR ports/tubing, there is already a problem with the oil control;
either the rings or the valve guides/seals. A healthy engine will have
only very light carbon build-up in the EGR and PCV circuits (and on
the sparkplug electrodes), even after 100K+ miles. One thing to look
for when purchasing a used vehicle, BTW.

One thing I have observed is that changing the make-up of the exhaust
gas stream via aftermarket fuel enrichment, removal of secondary air
injection, or prolonged operation with the ECU in "limp-home" mode
can, and most probably will, destroy the catalytic converter in short
order. The ceramic matrix actually _melts_ as a result of the extra
fuel . . .

Much different beast, but the EA81 engine in my old 4X4 GL hasn't had
a working EGR (or the "air suction valves" for that matter; I got
tired of the noise) for years. 230K and still starts on the first
bump, even on the coldest winter mornings. Ummmm, I _do_ have to
"tweak" this one to get it past the emissions test, tho; swap exhaust
"Y" pipe (for one with an intact Cat) and bleed extra air into the
intake manifold (I have a "special" vacuum fitting).

As someone faster than me once said:
"Two kinds of racers, boy; losers and cheaters" ;-)


ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[Hank]

Cautionary, because this information wasn't something I found when I
need to know it last March before I bought a used 1988 GL Subaru wagon.

The EGR s....

Well, the engine rebuilder recently said, oops, meant to say that the
PCV system clogged up damages the rings, not the EGR -- it was a Friday
afternoon and they had too many acronyms loose about the office.

Aside from those three letters, they stand beside the statement that
they see engines with the oil rings frozen or otherwise nonfunctional
on Subaru engines that have had the PCV system crimped or plugged.

 

[Hank]

Hi Hank, All!

Corrected by followup to my original post, and I'm sure you're correct;
the rebuilder said they meant to tell me it was the PCV valve being
plugged up that they observe goes with damaged oil rings eventually.

You may know of them if you've shopped for rebuilt Subaru engines,
you're in the same city.

As I've known for a long time -- the way to get good information on the
Internet is to post what I know and await correction.

Thank you!
Hank Roberts
N6VSB

 

[S]

Hi Hank!

Corrected by followup to my original post, and I'm sure you're correct;
the rebuilder said they meant to tell me it was the PCV valve being
plugged up that they observe goes with damaged oil rings eventually.

Ya, far more likely; crankcase gas _has_ to go somewhere! Older cars
rarely sealed tight enough that a failed PCV valve would cause
problems; the gas would just escape into the engine compartment. Newer
engines have the crankcase ventilation hoses and such buttoned up
pretty tight (gotta keep the EPA happy don't ya know), and a plugged
PCV valve can, conceivably, actually _pressurize_ the case, which
makes it way more likely that oil/combustion blow-by/other crankcase
spoo will work it's way into the combustion chamber. With predictable
results, as you have observed.

You may know of them if you've shopped for rebuilt Subaru engines,
you're in the same city.

Colorado Component Rebuilders? Or Facelli Motors? CCR is in Denver,
and is a reputable source for rebuilt Subaru motors. Facelli Motors is
a local shop (in my home town: Palmer Lake, CO); don't know if they do
rebuilds or not, but they seem to be knowledgable.
I've never used either source; a long-time friend owns the
Subaru/Toyota boneyard in Colorado Springs. If I need schtuff for my
cars (Subarus and a lonely Toyota as it turns out), I go down and cry
on Bobs shoulder . . . And short of installing windshields (and I plan
on learning how real soon; see my post on this subject on a.a.s.), I
do all of my own work. Isn't necessarily better, but at least I know
where to go to complain ;-)

As I've known for a long time -- the way to get good information on the
Internet is to post what I know and await correction.

Digest it all, toss the obviously spurious, RMS the rest.

N6VSB

73 DE KG0MB
Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101