Ubermensch

After moving into a new condo and moving job locations I was looking forward to my first weekend without a project in quite some time. I had a nice day on the slopes until I drove the 2001 C4 back home. On the ride a check engine light popped up. The car was running fine, oil pressure was good, temperature was good, so I figured it might be an emissions issue and I'd pull the code when I got home. I stopped for lunch on the way and when I restarted the car I got a loud screeching/squealing sound. I was about 40 miles from home at this point and figured the AOS had finally developed the problem I had read about. I hoped in to nurse it home and within 20 miles I noticed the car was running a bit rough...the check engine light went to blinking and I immediate pulled over to shut it down. When I shifted into neutral the engine died immediately. I had the car flatbed home.

The only codes the ECU stored were misfires on a couple of cylinders (1&3).

There appears to be a light residue in the oil fill cap (might just be due to short trips in winter).

The coolant seems noticeable darker in color.

At this point I suspect an intermix of the oil and coolant. I'll drain some oil and send it out for analysis to confirm.

Questions:

If the intermix is due to the AOS is it possible to flush the oil and coolant, replace the AOS and move on with life?

Any way to determine if the intermix cause additional damage when it shut down (short of a boroscope which I don't have).

If the intermix is due to a cracked head, is there any way to confirm this prior to a teardown of the engine?

Many Thanks,

Shawn

ivangene

sounds like AOS failed badly

check your coolant and oil - that will tell you its not an intermix

(no oil in coolant, no coolant in oil)

now to change that AOS and get the smile back and the worries gone

redridge

Might be cracked coil packs.... as well. The oil cooler is known to fail as well for intermix. If the intermix is bad.... gotta flush out the rads. GL.

ivangene

after seeing how bad the radiators get from intermix.... I would advise replacing them, its really really really hard to get all the stuff out....

I am hopeful you just have some small issue and will be up and running in no time

Ubermensch

I'm wondering about the misfiring codes. I guess I was thinking the worst that it might be coolant in the cylinders causing the misfires. The coil packs were replaced around 60k miles, but it is 108k miles now.

Any suggestions on how to confirm it's only the AOS and not a cracked head?

Thanks,

S.

ivangene

if it has a big enough vacuum leak it could cause misfire - just hoping for you...Macster has written several really in depth ways to check the AOS... search AOS posts by user - that should get you the info

C4CRNA

That loud squeal is indicititve of the AOS failing.
Hope thats it!
Did temp go up?
Did oil pressure do anything up or down?

Ubermensch

The oil pressure and temperature were both normal during this process. That was part of my reasoning for not worrying about the initial check engine light.

I pulled a sample of coolant last night and it actually looks perfectly clear with no oil residue. That certainly made me feel better about the possibility of an intermix. Next I'll drain the oil and send a sample off for analysis to confirm things on that side.

Based on some of Macster's earlier posts about diagnosing the AOS I pulled the intake and took a good look at the throttle body. The body and plate are soaked in oil. That seems to point very strongly at the AOS failing.

I'm starting to believe that the AOS failed during my drive. The subsequent oil being drawn into the chambers and the vacuum leak likely caused the misfires that were recorded by the ECU. Finally, when I shifted to neutral at the blinking check engine light the engine tried to reach idle but wasn't able to hold it due to the vacuum leak. That resulted in the engine dying.

I'm feeling a lot better about this situation now that it's looking like it's not a cracked head, but just a PIA AOS. I'll feel even better if the oil analysis comes up clean.

-Shawn

ivangene

pull the dip stick and look at the oil, if its "oil color" and noy cream in your coffee color.... I would not even send it out...seriously, in order to have an intermix big enought to throw a CEL your oil would be creamy brown...

but if you have coolant in the tank, (not low aka consumed) you are most likely OK....

AOS is not that bad....is this going to be a DIY or "take it in" job....?
If it did get oil into the intake I would clean what you can and maybe consider a set of new plugs too

Dharn55

Sounds like the AOS. When mine failed I had large amounts of oil in the intake/plenum.

If it is intermix cleaning the radiators is actually one on the easier parts to clean. You can remove them and take them to a radiator shop where then can hot flush them a few times to remove the goo. It is the tubes from the rear to the front of the car and the heater coil that are the bigger challenge. For the tubes I removed all the connecting hoses and used an electrical fish tape to draw rags through the tubes. Probably got 95% of the goo out. The heater coil I just let the system running flush it out. After I fixed my intermix I changed the coolant a few times including using a vacuum device to suck all the coolant out. I am sure that if I tested my coolant there would still be traces of oil in the system due to residue I could not get out. I am not really worried about that. If it was coolant in the oil I would be worried. I have over 10,000 miles since my fix so I am not worried about either these days.

redridge

This post is logical..... GL with the AOS R&R. Lots of diy info here. Let us know how you make out.

Ubermensch

1. It seems many people are handling this when the engine is already out. Others suggest dropping the transmission and lowering the engine. Still others are going in from the top and removing the intake. Is there any consensus on this if:
a) I have one scissor jack, one hydraulic jack, and four jack stands
b) I'm working in a public garage

I'm leaning towards going in from the top/side (removing the wheel) since it avoids me having to drop major components in a public area. This is a 2001 C4 MT if it impacts your feedback

2. Is it safe to drive the car in the current condition? I'd like to move it 1.5 miles to a more private garage. Towing is possible, but a huge pain due to low clearance at both garages. I'm think that if I disconnect the MAF it should run roughly but run.

Thanks again,

S.

ivangene

I opted to go from the top - Ferd (redridge) made the suggestion... it works OK with minimal tools and about as much stuff as you have for jacks

I lowered the motor (rear mounts) enough to gain some space (big help) and the lower bellows clamp almost beat me - I had hurt my hand and cound not squeeze the clamp and install it after at least an hour of trying I replaced it with a worm clamp - but not too tight so it didnt bit into the bellows -

overall a pretty easy job - just takes a lot of time

OH one other thing, I never liked the way the AOS went on... it just sort of pushes against the block hole to seal, never left me feeling like it went in right - but it did... I wasted a lot of time trying to determine if it was actually in or not

redridge

1. go to a garage with some heat.... this will prob take the whole day (8 hours going in from the top). But you still need to get under the car when working on the bellows and mounting screws.

a. Make sure they are good stands. Use the jack to put it under the engine end for insurance. Think safety.
b. your gonna be on your back for some time... you can drop the engine a couple of inches if you need more room.

2. I dont think you will damage the car going 1.5 miles .... if you keep the revs up. No need to pull the maf IMO.

Dharn55

You will want a set of these for the hose clamp