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AOS Intermix Possible

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Now I know why 1-3 might be running a little wet and rough... I know I've read this before, but came someone provide a little "comfort" here... <_< a cracked/failed AOS can be a source of intermix correct? Along with oil cooler and <cough> cracked head and <cough> blown expansion plug.

There was just a tiny amount of this stuff in there in the 1-3 tube only. Curiously none going to the 4-6 tube.


NO other evidence of intermix thus far, oil good, coolant good. Intake plenums a little oily but valves are clean.

Still pulling her apart. Maybe too soon to tell.


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The AOS on a 996 does have coolant running through it. Based on this I would think a crack/leak somewhere in the AOS could put a little coolant into the system. Haven't really heard of this. How does the oil itself look. The only oil in the AOS should be vapors so I would not expect to see oil in the coolant.

One thing to keep in mind on intermixes is that when the engine is off, and so the oil pressure is non-existent, and crankcase pressure is down, the coolant is still heated/pressurized, so it can force its way into the oil areas.

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Oil looks pretty clean for 750 miles. I would consider putting back in once my work is done, but will probably change it. Not a hint of coolant - then again I don't have an oil anaylsis machine in my garage. I'll probably send a sample off to Jake.

The coolant is sparkling clean. I just changed it about 100 miles ago.

I already have a new AOS ready to go and just about every pipe, clamp, tube, seal, and connector that goes with it.

If you see another thread I started here I noticed bank 1-3's plugs are all wet. Bank 4-6 are dry comparatively. I am guessing at this point that is either due to the AOS dumping oil or coolant into 1-3, or a rich condition. Just guessing at this point since I haven't cracked open any covers yet. I hadn't planned on going past the lifter carrier, but for my peace of mind I might have to remove the heads for further inspection. I don't know enough about the internals of the AOS to know if it's possible to fail for just 1-3 tube and not the 4-6 tube. Or perhaps the coolant breech/crack is so minute it makes it into 1-3, but not all the way over the top of the engine to 4-6??? Anyways I'm going to cut the old AOS in half, and then curse at it, and probably even smash it once I'm done with it.

This would be either dumb luck, or an incredible stroke of luck to have caught an intermix before it turned bad. The car was running pretty good before I removed the engine, albeit slightly rough and wobbly idle. Good power though. Not surprised about the idle with all the leaks my car has developed in 12 years. 4-6 AOS pipe connector, pretty much every o-ring associated with the AOS, all 6 spark tubes, both cam covers, the rear case bolts, oil filler tube, solenoid cover, and on and on and on. Even the oil filler tube decided to literally break in half while I was dropping the engine. I think it knew I had ordered another one to replace it. :rolleyes:. You wouldn't believe all the little souvenirs from people I found resting on top of the block.


I hope it's just the stupid plastic AOS though. Too bad the motorsports version doesn't fit in the 3.4L.

Before I start cracking into it. Now that I've got a good starting point to tackle for all of the various leaks, I've got the engine stripped down aside from the fuel rails, and it's bunged and prepped for a wash before the end of the week..


Pretty soon I'll be starting a thread here and rennlist, providing a website with all the pics I've taken so far.

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Thanks, yeah I learned the latex glove bung trick from Ed on Wheeler Dealers.

Actually you put a small cloth inside and then tie the glove around itself. Makes for a perfect water tight seal.

Just be sure to buy the kind that are resistant to solvents, oils, etc.

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