1. Home
  2. Subaru Cars Forum
  3. Plugged EGR system leads to burned oil rings over time -- cautionary

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

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.)

Reply to
Hank
Loading thread data ...

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

Reply to
Rick Courtright

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

formatting link
'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"

Reply to
Hank

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

Reply to
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.

Reply to
Hank

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

Reply to
Hank

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.

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 ;-)

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

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

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.