Petersa9

What is the best route to detect a head gasket failure? Can we pressurize from the spark plug tube and watch for bubbling in the coolant expansion tank? What would this prove or could I be getting false results being this could be a cracked cylinder.

Reason I'm asking is the tech pressurized the system again and only found coolant in cylinder 4. Appears the problem is near. Next step should be removing the engine And inspecting head gasket right?

I have the shop putting together estimates before yanking the motor on possible outcomes.

Macster

If you have the right shop the shop should tell you what the next step is.

If a bad head gasket is suspected a leak down test of at least the suspected cylinder and probably the cylinder on either side is what is called for if not all 6 cylinders.

You don't want to assume a head gasket leak will cause bubbles in the coolant tank. That's a long way away from the head gasket.

I would be inclined to drain the cooling system before leak down test. If there is leak in the gasket between the cooling system and the cylinder/head I want the air in the cylinder to leak out with as little interference or resistance so the pressure in the bad cylinder drops and clearly signals there is a leak.

With the cooling system empty then you can listen at the coolant tank for any sounds of escaping air.

Petersa9

Update!

Well, the shop wanted to drop the engine and disassemble and look at the block. I asked them to hold off since I wasn't comfortable they were on the right path.

After speaking with Jake and a few other AWESOME shops about a possible rebuild they mostly thought that this had something to do with the AOS. So, I advised my shop to take the intake off and look for oil, but instead they ran another pressure test and found that pressure was being allowed back into the crankcase. They ran the same test on another 996 in the shop and it didn't leak at all. This lead them to the diagnosis that the AOS is bad.

So, I dropped my new AOS, thermostat and water pump off and said install them...crossing my fingers in hopes it all ends here.

Macster

You asked the shop to remove the intake and check for oil and instead it did another pressure test?

And then you are relying on this shop to further work on the car?

I'd seriously consider finding another shop.

While I hope the problem is AOS related I'm having a hard time coming up with a way that pressure in the cylinders can make it into the crankcase via a bad AOS.

The AOS is connected to the crankcase and the intake. It has no responsibility for maintaining pressure in the cylinders. Certainly if there is a pressure leak in one or more cylinders air flow/sounds might be at the AOS as this is the only path for air inside the crankcase to make it to atmosphere as the air flows through the AOS to the intake manifold.

To put it another way: If one or cylinders are pressurized and pressure drops there is a leak in the cylinder, or head, or around the valves, or past/through a compromised head gasket.

If the engine was just overreved I'd guess bent valves but in this case I'm more inclined to believe a cracked head is the culprit. As it has been reported here and backed up by the distinct lack of posts on this failure mode head gasket failure is a rare event.

But the AOS/water pump/T-stat job is already underway I guess. Let's see how this works out.

Petersa9

Macster, I wish I knew. While I understand this reasoning I am an amateur at best.

The shop is doing all this work for a few hours, so the bill is low. Replacing the AOS will eliminate at least one possible cause.

Once the old AOS is removed is there a way to inspect it or test to see if it was bad?

Petersa9

Alright, glory is mine at last. My baby is back in the garage running like a champ. Turned out only to be a bad AOS. All this confusion mostly to do with my mechanic not be familiar enough with the m96. Seriously, I asked about the AOS a long time ago and he was set on d-chunking or cracked cylinder. So another grand to install the new AOS and I'm back in the road with a little less cash, better than a new engine.

When I picked it up it blew very little smoke and since then no more. Idles perfectly and sounds great. I'm in love again!

Thank you everyone!

Sneaky Pete

Glad you are up and running. The shop knew exactly what they were doing...now is the time to find a new mechanic.

Petersa9

Goes without saying, right?!

I ran into two other 996 owners the first day back on the road and it was odd, but both recommended a Porsche master tech at Reina Auto in Milwaukee. I test drove a 40th Anniversary with them a while back and they were great to work with. Might give them a shot.

Agent Jester

Had a similar experience at Mraz when I took my C2 in for the IMS and RMS. They kept pushing this "d-chunking" phenomenon I had never heard of instead of all the common issues I'd read about on this forum. That being said, they did a great job on the work. Glad to hear you're back up and running, it's definitely been a hard luck summer for you. And I'm jealous you got to drive that 40th anniversary at Reina, it didn't last long. I'd been meaning to go take a peek at that violet chroma flair paint and before I knew it, it was gone.

Sneaky Pete

Reina on Capital Drive in Brookfield. I have a few cars from them in the past. That's where I got the BMW 2002 from. Joe Reina is a decent guy. I actually grew about a mile away.

A little bit of irony......Mraz and Reina used to share space at that building before Mraz went to Pewaukee.

Good luck!

Petersa9

Might take the 996 to Reina now. It's been about 500 miles since I had the AOS replaced and this morning KITT decided to lay down a smoke screen. I was under hard acceleration taking a long sweeping turn through an industrial park at about 40-60mph. Which tells me it's nothing major, likely leftover oil from AOS swap and a ****ty job cleaning my intake out...maybe.

Engine sounded fine and everything else checked out. I think there may be a larger issue or possibly a little leftover oil sitting in the engine went into the intake.

My only reservation is that when this problem came up prior to the new AOS it exhibited the same behavior, to a "T." Now this could be a number of other items. Thoughts?

Ahsai

How's the oil level and do you have a manometer to check the AOS? Even a btand new unit can fail out of the box....ask me how I know.

Petersa9

I think I'll pick one up today from the science store and see what I get. thanks!

Ahsai

Ok, if you're getting those U-shape tube ones filled with liquid, I suggest filling it with engine oil instead and multiply your reading by 0.9 to get the reading in inch H2O (should be around 5" H2O)....in case you engine sucks the liquid into it due to excessive vacuum.

alpine003

Either get the same one as Ahsai or I(Pyle digital manometer) or you can just make your own.

No need to go buy a liquid version.