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patman

Oil in coolant, heads not cracked?

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Hi guys,

 

I've been on here for a while but never really needed to post before. My wife has a 1999 911 Tiptronic, with ~111k miles. We have had the car for 3 years, and had ~60k miles on it when we got it. I can't speak for the previous owner, but since we have had it it has been carefully maintained, oil changed every 5k, never overheated, overrevved, or otherwise abused. My wife daily drives the car and is pretty easy on it as far as I can tell.

 

Anyway, a few thousand miles ago I replaced the (cracked) coolant tank, and drained and flushed the coolant. At the time I noticed a tiny bit of residue in the oil, but not enough to make me really notice. Recently we have been noticing more and more residue, so I drained and flushed again a month or so ago, and found a couple tablespoons of emulsified oil. Last week I decided it was time to figure out the problem, so drained the coolant again. This time it was more like a cup or so of goop. I pulled the oil cooler and pressure tested it, without finding any leaks.

 

I drained the oil, with no trace of coolant. Speaking of which, there has never been any indication of coolant in the oil, or residue under the oil cap.

 

After a bit of online research, I concluded that the most likely issue was a cracked head. I couldn't see anything throught the spark plug holes, so pulled the engine. I have not opened up a Porsche engine before, but had all the tools except a cam holder, which I fabbed up last week, so I started tearing it down.

 

I have now pulled the heads, and could not find any visible cracks or anything. Today I cleaned them up and dye-penetrant tested them, again with no indication of cracks.

 

A couple of things I noticed: the machined surface where the cam carrier mounts is very rough, like it was milled with a dull tool. I know this isn't a sealing surface, but I am wondering if this is typical or does this indicate that someone has worked on the heads in the past? I did find some little bits of rag in the heads, so either Porsche is more sloppy than I thought or someone has been in here before.

 

The head gaskets seemed not to be in great shape: the rubber surface was very gummy, not sure if this is normal. No obvious leak paths were visible though.

 

Anyway, my question is, is there somewhere else that high pressure oil could potentially enter the coolant?

I have heard of cylinder cracking, but cylinders look perfect at least from the top side. Do the cracks usually stay below the BDC piston location, and is there any way to see this without splitting the cases?

 

I am going to try and find someone local who can pressure test the heads this week, but I am wondering if I have overlooked any other possible causes?

 

Thanks in advance,

Pat

 

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A couple of things I noticed: the machined surface where the cam carrier mounts is very rough, like it was milled with a dull tool. I know this isn't a sealing surface, but I am wondering if this is typical or does this indicate that someone has worked on the heads in the past? I did find some little bits of rag in the heads, so either Porsche is more sloppy than I thought or someone has been in here before.

 

The head gaskets seemed not to be in great shape: the rubber surface was very gummy, not sure if this is normal. No obvious leak paths were visible though.

 

This caught my eye "Head gaskets not in great shape, rubber surface was very gummy". Head gaskets on these cars are extremely strong, material is multi-layered steel, can't believe that someone has DIY'ed this gasket from some other material? Please post a picture of your gasket and while at it, also cam carrier mounts.

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Also, if you suspect your engine is fine, could the ATF heat exchanger cause such symptoms in your case?

 

See the cooling diagram on this message.

M96 Cooling System.pdf

Edited by Domiac

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It isn't the ATF heat exchanger, as I pressure tested that as well. (unless maybe it is an issue in the housing somewhere). ATF looked fine when I drained it as well.

 

As far as the head gasket, the metal gasket seems OK, but it has black gummy stuff on it which is kind of nasty. I'm not sure if the new gaskets are rubber faced, or if it was assembled with a hylomar type product, and if so if this is normal practice?

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Well, the shop that was allegedly able to pressure test my heads said they can't do it, so I decided to pull the black case halves apart and look at them. 

 

Looks like my engine must have been one of the porous blocks, because there are several welded places on the case halves. I am assuming that means that my issue is probably porosity in between one of the oil and coolant passages, but I'm not sure if I will be able to figure out which one.

 

Does anyone have any idea how many places there are high pressure oil passages that run near coolant areas?

 

Seems like I might end up in the used engine market pretty soon, or maybe part out the car if I think I can get enough for it...

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Any news on this? Patman, pictures would be much appreciated.

 

Hopefully some others may provide more information to your questions.

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I took the heads to a local machine shop to be pressure tested yesterday, hopefully will hear results today.

I spent all weekend pressure testing and dye-pen testing different parts of the crakcase halves. They are pretty awful castings, which makes me suspicious, but I couldn't find any place that actually leaked.

 

I did call one of the popular Porsche rebuild shops and talked to them. I can't afford their prices, but I was surprised to hear them say that the weld repairs to the case were likely done by Porsche, and that they see this all the time. They seemed to think that since my car is a 99, it is more likely the block than the heads.

 

I will try to post pics later today if I can get them uploaded.

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Edit: The most common cause for intermix in the 3.4L is a cracked head.  They can be fixed (Dharn55 would be a good guy to contact if you have to go this route)... the 3.4L does have thinner cylinder walls (d-chunk, etc).

Edited by Silver_TT

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True, but I believe it could cause coolant in the oil and not vice versa as the original poster has stated he saw the intermix in the coolant tank (aka oil in the coolant). . ?

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Turns out, my title is wrong. I have not gone to look at the heads, but the shop called me last night and said one of them is indeed cracked.

It sounds like it is a small crack into the edge of one of the oil passages, which is perhaps why the dye-pen didn't pick it up. I'm going to look at it at lunchtime today; I am hoping it is in an area where I can just grind it out and weld it up, but we will see.

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Sorry to hear that but at least it's not the block -- it can be fixed.  Contact Dharn55 (Doug Harn) if you need to talk to someone who has been there on the same car........ hopefully your crack is just hairline and it sounds like it should be based on what you described (a very light intermix, not the "milkshake" others have seen).  Maybe you get lucky and it will be on the easier side for them to patch up.  Keep us posted.

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Hope you found your issue and are able to fix it with reasonable budget! Please send pics!

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